Patent Publication Number: US-7582804-B2

Title: Process for the preparation of a tetraalkycyclobutane-1,3-diol using a promoted-copper catalyst

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/872,469 filed on Dec. 2, 2006, which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to the production of a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In one embodiment, the present invention relates to the production of a 2,2,4,4-tetraalkylcyclobutane-1,3-diol by hydrogenation of a 2,2,4,4-tetraalkylcyclobutane-1,3-dione in the presence of a promoted copper-based catalyst. 
     BACKGROUND OF THE INVENTION 
     2,2,4,4-Tetramethylcyclobutane-1,3-diol is an important intermediate for producing a variety of polymeric materials having advantageous properties. For example, polyesters derived from dicarboxylic acids and 2,2,4,4-tetramethylcyclobutane-1,3-diol can possess higher glass transition temperatures, superior weatherability, and/or improved hydrolytic stability compared to polyesters prepared from other commonly-used, polyester forming diols. A 2,2,4,4-tetramethylcyclobutane-1,3-diol of Formula I is typically produced by the catalytic hydrogenation of the corresponding 2,2,4,4-tetramethylcyclobutane-1,3-dione as shown below. 
     
       
         
         
             
             
         
       
     
     Typically, the hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione produces the corresponding 2,2,4,4-tetramethylcyclobutane-1,3-diol as a mixture of cis and trans isomers. It would be desirable to produce 2,2,4,4-tetramethylcyclobutane-1,3-diol with a specific cis:trans isomer ratio in order to control glass transition temperatures and/or crystallization rates in copolyesters. 
     SUMMARY OF THE INVENTION 
     The present disclosure relates to the production of a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In one embodiment, the present invention relates to the production of a 2,2,4,4-tetraalkylcyclobutane-1,3-diol by hydrogenation of a 2,2,4,4-tetraalkylcyclobutane-1,3-dione in the presence of a promoted copper-based catalyst. 
     In one embodiment, the present invention relates to a process for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals each independently have 1 to 8 carbon atoms. 
     In one embodiment, the present invention relates to a process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol, comprising contacting 2,2,4,4-tetramethylcyclobutane-1,3-dione, a promoted copper-based catalyst, a non-protic solvent, and hydrogen in a hydrogenation zone under conditions of temperature and pressure sufficient to form 2,2,4,4-tetramethylcyclobutane-1,3-diol. 
     In one embodiment, the present invention relates to a process comprising: (1) feeding isobutyric anhydride to a pyrolysis zone, wherein the isobutyric anhydride is heated at a temperature of 350° C. to 600° C. to produce a vapor effluent comprising dimethylketene, isobutyric acid, and unreacted isobutyric anhydride; (2) cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor; (3) feeding the dimethylketene vapor to an absorption zone, wherein the dimethylketene vapor is contacted with and dissolved in a solvent comprising an ester containing 4 to 20 carbon atoms and consisting of residues of an aliphatic carboxylic acid and an alkanol to produce an absorption zone effluent comprising a solution of dimethylketene in the solvent; (4) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated at a temperature ranging from 70° C. to 140° C. to convert dimethylketene to 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and (5) contacting the 2,2,4,4-tetramethylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetramethylcyclobutane-1,3-diol. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. One or more of the objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present disclosure may be understood more readily by reference to the following detailed description of certain embodiments of the invention and the working examples. 
     In accordance with the purpose of this invention, certain embodiments of the invention are described in the Summary of the Invention and are further described herein below. Also, other embodiments of the invention are described herein. 
     The term “promoted copper-based catalyst” refers to a copper-based catalyst that has been promoted by a promoter compound. The copper-based catalyst is promoted by contacting the catalyst with a solution of a promoter compound under appropriate conditions. Appropriate promoting conditions are exemplified, but not limited to, the methods in the examples below. Other conventional methods of applying promoters to catalysts are well-known to those of skill in the art. Applicants make no representation regarding the nature of the interaction of the promoter compound and the copper-based catalyst, but instead contemplate as within the scope of the present invention all promoted copper-based catalysts that are active in the claimed processes. In one embodiment, the yield of the hydrogenation reaction is greater than 10%, for example, greater than 40%, for example, greater than 50%, for example, greater than 60%, for example, greater than 70%, for example, greater than 80%, for example, greater than 90%. 
     The terms “Group 1 of the Periodic Table,” or “Group 1,” and “Group 1 metal” refer to the subgroup numbering system adopted by the International union of Pure and Applied Chemistry in 1984, and refer to the elements of Group 1 of the Periodic Table, excluding hydrogen. That is, Group 1 refers to lithium, sodium, potassium, rubidium, and cesium. The terms “Group 6 of the Periodic Table,” or “Group 6,” and “Group 6 metal” refer to the subgroup numbering system adopted by the International union of Pure and Applied Chemistry in 1984, and refer to the elements of Group 6 of the Periodic Table. That is, Group 6 refers to chromium, molybdenum, and tungsten. The terms “Group 7 of the Periodic Table,” or “Group 7,” and “Group 7 metal” refer to the subgroup numbering system adopted by the International union of Pure and Applied Chemistry in 1984, and refer to the elements of Group 7 of the Periodic Table. That is, Group 7 refers to manganese, technetium, and rhenium. The terms ruthenium, cobalt, “Group 1 metal,” “Group 6 metal,” and “Group 7 metal” include, for example and without limitation, the zero valent metal, the metal in ionic form, and the metal in an alloy. 
     The term copper-based catalyst refers to a catalyst comprising copper including, for example and without limitation, zero valent copper, copper in an ionic form, and copper in an alloy. 
     Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Further, the ranges stated in this disclosure and the claims are intended to include the entire range specifically and not just the endpoint(s). For example, a range stated to be 0 to 10 is intended to disclose all whole numbers between 0 and 10 such as, for example, 1, 2, 3, 4, etc., as well as the endpoints 0 and 10. Also, a range associated with chemical substituent groups such as, for example, “C 1  to C 5  hydrocarbons,” is intended to specifically include and disclose C 1  and C 5  hydrocarbons as well as C 2 , C 3 , and C 4  hydrocarbons. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. 
     As used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include their plural referents unless the context clearly dictates otherwise. For example, reference to the processing or making of a “catalyst,” or a “promoter,” is intended to include the processing or making of a plurality of catalysts, or promoters. References to a composition containing or including “a” promoter or “a” catalyst is intended to include other promoters or other catalysts, respectively, in addition to the one named. 
     By “comprising” or “containing” or “including” we mean that at least the named compound, element, particle, or method step, etc., is present in the composition or article or method, but we do not exclude the presence of other compounds, catalysts, materials, particles, method steps, etc., even if the other such compounds, materials, particles, method steps, etc., have the same function as what is named, unless expressly excluded in the claims. 
     It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps before or after the combined recited steps or intervening method steps between those steps expressly identified. Moreover, the lettering of process steps or ingredients is a convenient means for identifying discrete activities or ingredients and it is to be understood that the recited lettering can be arranged in any sequence, unless otherwise indicated. 
     In one embodiment, the present invention provides processes for making a 2,2,4,4-tetraalkylcyclobutane-1,3-diol by hydrogenation of a 2,2,4,4-tetraalkylcyclobutane-1,3-dione. In a general embodiment, the invention provides processes for making a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a copper-based catalyst promoted with ruthenium, a Group 1 metal, a Group 6 metal, a Group 7 metal, or a Group 9 metal under hydrogenation conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In another general embodiment, the invention provides a process for making a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a cesium-promoted copper-based catalyst under hydrogenation conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In another general embodiment, the invention provides a process for making a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a chromium-promoted copper-based catalyst under hydrogenation conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In another general embodiment, the invention provides a process for making a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a cobalt-promoted copper-based catalyst under hydrogenation conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In another general embodiment, the invention provides a process for making a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a rhenium-promoted copper-based catalyst under hydrogenation conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In another general embodiment, the invention provides a process for making a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a ruthenium-promoted copper-based catalyst under hydrogenation conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In one embodiment, the present invention is useful for the preparation of 2,2,4,4-tetramethylcyclobutane-1,3-diol from 2,2,4,4-tetramethylcyclobutane-1,3-dione. 
     The hydrogenation reaction of 2,2,4,4-tetraalkylcyclobutane-1,3-dione to produce a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II is shown below: 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 3 , and R 4  each independently represent an alkyl radical, for example, a lower alkyl radical having 1 to 8 carbon atoms. The alkyl radicals may be linear, branched, or a combination of linear and branched alkyl radicals. The 2,2,4,4-tetraalkylcyclobutane-1,3-dione, for example, 2,2,4,4-tetramethylcyclobutane-1,3-dione, is hydrogenated to the corresponding 2,2,4,4-tetraalkylcyclobutane-1,3-diol, for example, 2,2,4,4-tetramethylcyclobutane-1,3-diol, in accordance with the present processes. 
     In one embodiment, the alkyl radicals R 1 , R 2 , R 3 , and R 4  on the 2,2,4,4-tetraalkylcyclobutane-1,3-dione each independently have 1 to 8 carbon atoms. Other 2,2,4,4-tetraalkylcyclobutane-1,3-diones that are suitably reduced to the corresponding diols include, but are not limited to, 2,2,4,4-tetraethylcyclobutane-1,3-dione, 2,2,4,4-tetra-n-propylcyclobutane-1,3-dione, 2,2,4,4-tetra-n-butylcyclobutane-1,3-dione, 2,2,4,4-tetra-n-pentylcyclobutane-1,3-dione, 2,2,4,4-tetra-n-hexylcyclobutane-1,3-dione, 2,2,4,4-tetra-n-heptylcyclobutane-1,3-dione, 2,2,4,4-tetra-n-octylcyclobutane-1,3-dione, 2,2-dimethyl-4,4-diethylcyclobutane-1,3-dione, 2-ethyl-2,4,4-trimethylcyclobutane-1,3-dione, 2,4-dimethyl-2,4-diethyl-cyclobutane-1,3-dione, 2,4-dimethyl-2,4-di-n-propylcyclobutane-1,3-dione, 2,4-n-dibutyl-2,4-diethylcyclobutane-1,3-dione, 2,4-dimethyl-2,4-diisobutylcyclobutane-1,3-dione, and 2,4-diethyl-2,4-diisoamylcyclobutane-1,3-dione. 
     In other embodiments, the alkyl radicals R 1 , R 2 , R 3 , and R 4  on the 2,2,4,4-tetraalkylcyclobutane-1,3-dione each independently have 1 to 6 carbon atoms, or 1 to 5 carbon atoms, or 1 to 4 carbon atoms, or 1 to 3 carbon atoms, or 1 to 2 carbon atoms. In another embodiment, the alkyl radicals R 1 , R 2 , R 3 , and R 4  on the 2,2,4,4-tetraalkylcyclobutane-1,3-dione each have 1 carbon atom. 
     In one embodiment, the promoter compound comprises ruthenium. In one embodiment, the promoter compound comprises cobalt. In one embodiment, the promoter compound comprises a Group 1 metal. In one embodiment, the promoter compound comprises a Group 6 metal. In one embodiment, the promoter compound comprises a Group 7 metal. 
     The compounds used as promoter compounds include, but are not limited to, water soluble compounds. Such compounds include, but are not limited to, their oxides, hydroxides, and alkoxides, and the corresponding salts such as acetates, carbonates, phosphates, and nitrates. 
     The amount of the promoter compound on the catalyst depends upon the promoting conditions. In one embodiment, the amount of the promoter compound on the catalyst ranges from 0.01 to 10 weight percent (abbreviated herein as “wt %”) based upon the total weight of the catalyst. For example, certain processes of the present invention use a copper-based catalyst promoted with a promoter compound comprising 0.01 to 10 weight percent (wt %) of the promoter compound, based on the total weight of the promoted copper-based catalyst. Other examples of the promoter compound levels on the promoted copper-based catalyst are 0.05 to 7 wt % of the promoter compound and 1 to 5 wt % of the promoter compound. The copper ranges from 1 to 95 wt %, or 1 to 80 wt %, or 20 to 80 wt %, or 40 to 70 wt %, based on the total weight of the catalyst. 
     In one embodiment, the promoted copper-based catalysts of these novel processes comprise ruthenium. In one embodiment, the promoted copper-based catalysts of these novel processes comprise cesium. In another embodiment, the promoted copper-based catalysts of these novel processes comprise chromium. In another embodiment, the promoted copper-based catalysts of these novel processes comprise rhenium. In yet another embodiment, the promoted copper-based catalysts of these novel processes comprise cobalt. 
     In one embodiment, the copper-based catalyst is promoted with ruthenium. The amount of the ruthenium compound that may be incorporated by the copper-based catalyst depends upon the promoting conditions but, for example, may range from 0.01 to 10 weight percent (abbreviated herein as “wt %”) based upon the total weight of the promoted copper-based catalyst. For example, in some embodiments, the processes of the present invention may use a copper-based catalyst promoted with ruthenium comprising 0.01 to 10 weight percent (wt %) ruthenium, based on the total weight of the promoted copper-based catalyst. Other examples of ruthenium promoting levels on the promoted copper-based catalyst are 0.05 to 7 wt % ruthenium and 1 to 5 wt % ruthenium. 
     In one embodiment, the copper-based catalyst is promoted with cobalt. The amount of the cobalt compound that may be incorporated by the copper-based catalyst depends upon the promoting conditions but, for example, may range from 0.01 to 10 weight percent (abbreviated herein as “wt %”) based upon the total weight of the promoted copper-based catalyst. For example, in some embodiments, the processes of the present invention may use a copper-based catalyst promoted with cobalt comprising 0.01 to 10 weight percent (wt %) cobalt, based on the total weight of the promoted copper-based catalyst. Other examples of cobalt promoting levels on the promoted copper-based catalyst are 0.05 to 7 wt % cobalt and 1 to 5 wt % cobalt. 
     In one embodiment, the copper-based catalyst is promoted with a Group 1 metal, for example, cesium. The amount of the cesium compound that may be incorporated by the copper-based catalyst depends upon the promoting conditions but, for example, may range from 0.01 to 10 weight percent (abbreviated herein as “wt %”) based upon the total weight of the promoted copper-based catalyst. For example, in some embodiments, the processes of the present invention may use a copper-based catalyst promoted with cesium comprising 0.01 to 10 weight percent (wt %) cesium, based on the total weight of the promoted copper-based catalyst. Other examples of cesium promoting levels on the promoted copper-based catalyst are 0.05 to 7 wt % cesium and 1 to 5 wt % cesium. 
     In one embodiment, the copper-based catalyst is promoted with a Group 6 metal, for example, chromium. The amount of the chromium compound that may be incorporated by the copper-based catalyst depends upon the promoting conditions but, for example, may range from 0.01 to 10 weight percent (abbreviated herein as “wt %”) based upon the total weight of the promoted copper-based catalyst. For example, in some embodiments, the processes of the present invention may use a copper-based catalyst promoted with chromium comprising 0.01 to 10 weight percent (wt %) chromium, based on the total weight of the promoted copper-based catalyst. Other examples of chromium promoting levels on the promoted copper-based catalyst are 0.05 to 7 wt % chromium and 1 to 5 wt % chromium. 
     In one embodiment, the copper-based catalyst is promoted with a Group 7 metal, for example, rhenium. The amount of the rhenium compound that may be incorporated by the copper-based catalyst depends upon the promoting conditions but, for example, may range from 0.01 to 10 weight percent (abbreviated herein as “wt %”) based upon the total weight of the promoted copper-based catalyst. For example, in some embodiments, the processes of the present invention may use a copper-based catalyst promoted with rhenium comprising 0.01 to 10 weight percent (wt %) rhenium, based on the total weight of the promoted copper-based catalyst. Other examples of rhenium promoting levels on the promoted copper-based catalyst are 0.05 to 7 wt % rhenium and 1 to 5 wt % rhenium. 
     Suitable supports for the promoted copper-based catalysts include, but are not limited to, silica, alumina, aluminosilicate, silica/alumina, kieselguhr, titania, graphite, silicon carbide, carbon, zirconia, chromate, barium chromate, zinc oxide, clay, and alumina-clay Suitable forms of the support include powder, extrudate, spheres, or pellets. 
     The processes typically are conducted at temperatures in the range of 75° C. to 250° C. The processes typically are conducted at pressures in the range of 689 kPa (100 psi) (7 bar) to 41,368 kPa (6000 psi) (420 bar). Further examples of temperatures and/or pressures at which the processes of the invention may be operated are 120° C. to 200° C. at 1380 kPa (200 psi) (14 bar) to 20,684 kPa (3000 psi) (207 bar), and 130° C. to 180° C. at 2068 kPa (300 psi) (21 bar) to 14,789 kPa (2000 psi) (140 bar). For certain embodiments of the present invention, the hydrogenation process has a temperature ranging from 130° C. to 140° C. and a pressure ranging from 3450 kPa (500 psi) (34.5 barg) to 10000 kPa (1450 psi) (100 barg). For certain embodiments of the present invention, the hydrogenation process has a temperature ranging from 160° C. to 170° C. and a pressure ranging from 3450 kPa (500 psi) (34.5 barg) to 10000 kPa (1450 psi) (100 barg). 
     For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 250° C., 80° C. to 250° C., 90° C. to 250° C., 100° C. to 250° C., 110° C. to 250° C., 120° C. to 250° C., 130° C. to 250° C., 140° C. to 250° C., 150° C. to 250° C., 160° C. to 250° C., 170° C. to 250° C., 180° C. to 250° C., 190° C. to 250° C., 200° C. to 250° C., 210° C. to 250° C., 220° C. to 250° C., 230° C. to 250° C., or 240° C. to 250° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 240° C., 80° C. to 240° C., 90° C. to 240° C., 100° C. to 240° C., 110° C. to 240° C., 120° C. to 240° C., 130° C. to 240° C., 140° C. to 240° C., 150° C. to 240° C., 160° C. to 240° C., 170° C. to 240° C., 180° C. to 240° C., 190° C. to 240° C., 200° C. to 240° C., 210° C. to 240° C., 220° C. to 240° C., or 230° C. to 240° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 230° C., 80° C. to 230° C., 90° C. to 230° C., 100° C. to 230° C., 110° C. to 230° C., 120° C. to 230° C., 130° C. to 230° C., 140° C. to 230° C., 150° C. to 230° C., 160° C. to 230° C., 170° C. to 230° C., 180° C. to 230° C., 190° C. to 230° C., 200° C. to 230° C., 210° C. to 230° C., or 220° C. to 230° C. 
     For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 220° C., 80° C. to 220° C., 90° C., to 220° C., 100° C. to 220° C., 110° C. to 220° C., 120° C. to 220° C., 130° C. to 220° C., 140° C. to 220° C., 150° C. to 220° C., 160° C. to 220° C., 170° C. to 220° C., 180° C. to 220° C., 190° C. to 220° C., 200° C. to 220° C., or 210° C. to 220° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 210° C., 80° C. to 210° C., 90° C. to 210° C., 100° C. to 210° C., 110° C. to 210° C., 120° C. to 210° C., 130° C. to 210° C., 140° C. to 210° C., 150° C. to 210° C., 160° C. to 210° C., 170° C. to 210° C., 180° C. to 210° C., 190° C. to 210° C., or 200° C. to 210° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 200° C., 80° C. to 200° C., 90° C., to 200° C., 100° C. to 200° C., 110° C. to 200° C., 120° C. to 200° C., 130° C. to 200° C., 140° C. to 200° C., 150° C. to 200° C., 160° C. to 200° C., 170° C. to 200° C., 180° C. to 200° C., or 190° C. to 200° C. 
     For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 190° C., 80° C. to 190° C., 90° C., to 190° C., 100° C. to 190° C., 110° C. to 190° C., 120° C. to 190° C., 130° C. to 190° C., 140° C. to 190° C., 150° C. to 190° C., 160° C. to 190° C., 170° C. to 190° C., or 180° C. to 190° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 180° C., 80° C. to 180° C., 90° C. to 180° C., 100° C. to 180° C., 110° C. to 180° C., 120° C. to 180° C., 130° C. to 180° C., 140° C. to 180° C., 150° C. to 180° C., 160° C. to 180° C., or 170° C. to 180° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 170° C., 80° C. to 170° C., 90° C. to 170° C., 100° C. to 170° C., 110° C. to 170° C., 120° C. to 170° C., 130° C. to 170° C., 140° C. to 170° C., 150° C. to 170° C., or 160° C. to 170° C. 
     For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 160° C., 80° C. to 160° C., 90° C. to 160° C., 100° C. to 160° C., 110° C. to 160° C., 120° C. to 160° C., 130° C. to 160° C., 140° C. to 160° C., or 150° C. to 160° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 150° C., 80° C. to 150° C., 90° C. to 150° C., 100° C. to 150° C., 110° C. to 150° C., 120° C. to 150° C., 130° C. to 150° C., or 140° C. to 150° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 140° C., 80° C. to 140° C., 90° C. to 140° C., 100° C. to 140° C., 110° C. to 140° C., 120° C. to 140° C., or 130° C. to 140° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 130° C., 80° C. to 130° C., 90° C. to 130° C., 100° C. to 130° C., 110° C. to 130° C., or 120° C. to 130° C. 
     For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 120° C., 80° C. to 120° C., 90° C. to 120° C., 100° C. to 120° C., or 110° C. to 120° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 110° C., 80° C. to 110° C., 90° C. to 110° C., or 100° C. to 110° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 100° C., 80° C. to 100° C., or 90° C. to 100° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 90° C., or 80° C. to 90° C. For certain embodiments of the present invention, the hydrogenation process has a temperature range chosen from 75° C. to 80° C. 
     For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 6000 psi, 200 psi to 6000 psi, 300 psi to 6000 psi, 400 psi to 6000 psi, 500 psi to 6000 psi, 1000 psi to 6000 psi, 1500 psi to 6000 psi, 2000 psi to 6000 psi, 2500 psi to 6000 psi, 3000 psi to 6000 psi, 3500 psi to 6000 psi, 4000 psi to 6000 psi, 4500 psi to 6000 psi, 5000 psi to 6000 psi, or 5500 psi to 6000 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 5500 psi, 200 psi to 5500 psi, 300 psi to 5500 psi, 400 psi to 5500 psi, 500 psi to 5500 psi, 1000 psi to 5500 psi, 1500 psi to 5500 psi, 2000 psi to 5500 psi, 2500 psi to 5500 psi, 3000 psi to 5500 psi, 3500 psi to 5500 psi, 4000 psi to 5500 psi, 4500 psi to 5500 psi, or 5000 psi to 5500 psi. 
     For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 5000 psi, 200 psi to 5000 psi, 300 psi to 5000 psi, 400 psi to 5000 psi, 500 psi to 5000 psi, 1000 psi to 5000 psi, 1500 psi to 5000 psi, 2000 psi to 5000 psi, 2500 psi to 5000 psi, 3000 psi to 5000 psi, 3500 psi to 5000 psi, 4000 psi to 5000 psi, or 4500 psi to 5000 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 4500 psi, 200 psi to 4500 psi, 300 psi to 4500 psi, 400 psi to 4500 psi, 500 psi to 4500 psi, 1000 psi to 4500 psi, 1500 psi to 4500 psi, 2000 psi to 4500 psi, 2500 psi to 4500 psi, 3000 psi to 4500 psi, 3500 psi to 4500 psi, or 4000 psi to 4500 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 4000 psi, 200 psi to 4000 psi, 300 psi to 4000 psi, 400 psi to 4000 psi, 500 psi to 4000 psi, 1000 psi to 4000 psi, 1500 psi to 4000 psi, 2000 psi to 4000 psi, 2500 psi to 4000 psi, 3000 psi to 4000 psi, or 3500 psi to 4000 psi. 
     For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 3500 psi, 200 psi to 3500 psi, 300 psi to 3500 psi, 400 psi to 3500 psi, 500 psi to 3500 psi, 1000 psi to 3500 psi, 1500 psi to 3500 psi, 2000 psi to 3500 psi, 2500 psi to 3500 psi, or 3000 psi to 3500 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 3000 psi, 200 psi to 3000 psi, 300 psi to 3000 psi, 400 psi to 3000 psi, 500 psi to 3000 psi, 1000 psi to 3000 psi, 1500 psi to 3000 psi, 2000 psi to 3000 psi, or 2500 psi to 3000 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 2500 psi, 200 psi to 2500 psi, 300 psi to 2500 psi, 400 psi to 2500 psi, 500 psi to 2500 psi, 1000 psi to 2500 psi, 1500 psi to 2500 psi, 2000 psi to 2500 psi. 
     For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 2000 psi, 200 psi to 2000 psi, 300 psi to 2000 psi, 400 psi to 2000 psi, 500 psi to 2000 psi, 1000 psi to 2000 psi, or 1500 psi to 2000 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 1500 200 psi to 1500 psi, 300 psi to 1500 psi, 400 psi to 1500 psi, 500 psi to 1500 psi, or 1000 psi to 1500 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 1000 psi, 200 psi to 1000 psi, 300 psi to 1000 psi, 400 psi to 1000 psi, or 500 psi to 1000 psi. 
     For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 500 psi, 200 psi to 500 psi, 300 psi to 500 psi, or 400 psi to 500 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 400 psi, 200 psi to 400 psi, or 300 psi to 400 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 300 psi, or 200 psi to 300 psi. For certain embodiments of the present invention, the hydrogenation process has a pressure range chosen from 100 psi to 200 psi. 
     It is contemplated that the processes of the invention can be carried out at least one of the temperature ranges disclosed herein and at least one of the pressure ranges disclosed herein. 
     The source and purity of the hydrogen gas used in the processes of the present invention are not critical. The hydrogen gas used in the processes may comprise fresh hydrogen or a mixture of fresh hydrogen and recycled hydrogen. The hydrogen gas can be a mixture of hydrogen and, optionally, minor amounts, typically less than 30 mole %, of components such as CO and CO 2 , and inert gases, such as argon, nitrogen, or methane. Typically, the hydrogen gas comprises at least 70 mole % of hydrogen. For example, the hydrogen gas comprises at least 90 mole % or, in another example, at least 97 mole %, of hydrogen. The hydrogen gas may be obtained from any of the conventional sources well known in the art such as, for example, by partial oxidation or steam reforming of natural gas. Pressure swing absorption can be used if a high purity hydrogen gas is desired. If hydrogen gas recycle is utilized in one of the processes, then the recycle hydrogen gas may contain minor amounts of one or more products of the hydrogenation reaction which have not been fully condensed in the product recovery stage downstream from the hydrogenation zone. 
     The hydrogenation of 2,2,4,4-tetraalkylcyclobutane-1,3-dione typically produces cis-2,2,4,4-tetraalkylcyclobutane-1,3-diol and trans-2,2,4,4-tetraalkylcyclobutane-1,3-diol. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.0 or 1.6 to 0.0 or 1.5 to 0.0 or 1.4 to 0.0 or 1.3 to 0.0 or 1.2 to 0.0 or 1.1 to 0.0 or 1.0 to 0.0 or 0.9 to 0.0 or 0.8 to 0.0 or 0.7 to 0.0 or 0.6 to 0.0 or 0.5 to 0.0 or 0.4 to 0.0 or 0.3 to 0.0 or 0.2 to 0.0 or 0.1 to 0.0. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.1 or 1.6 to 0.1 or 1.5 to 0.1 or 1.4 to 0.1 or 1.3 to 0.1 or 1.2 to 0.1 or 1.1 to 0.1 or 1.0 to 0.1 or 0.9 to 0.1 or 0.8 to 0.1 or 0.7 to 0.1 or 0.6 to 0.1 or 0.5 to 0.1 or 0.4 to 0.1 or 0.3 to 0.1 or 0.2 to 0.1. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.2 or 1.6 to 0.2 or 1.5 to 0.2 or 1.4 to 0.2 or 1.3 to 0.2 or 1.2 to 0.2 or 1.1 to 0.2 or 1.0 to 0.2 or 0.9 to 0.2 or 0.8 to 0.2 or 0.7 to 0.2 or 0.6 to 0.2 or 0.5 to 0.2 or 0.4 to 0.2 or 0.3 to 0.2. 
     In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.3 or 1.6 to 0.3 or 1.5 to 0.3 or 1.4 to 0.3 or 1.3 to 0.3 or 1.2 to 0.3 or 1.1 to 0.3 or 1.0 to 0.3 or 0.9 to 0.3 or 0.8 to 0.3 or 0.7 to 0.3 or 0.6 to 0.3 or 0.5 to 0.3 or 0.4 to 0.3. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.4 or 1.6 to 0.4 or 1.5 to 0.4 or 1.4 to 0.4 or 1.3 to 0.4 or 1.2 to 0.4 or 1.1 to 0.4 or 1.0 to 0.4 or 0.9 to 0.4 or 0.8 to 0.4 or 0.7 to 0.4 or 0.6 to 0.4 or 0.5 to 0.4. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.5 or 1.6 to 0.5 or 1.5 to 0.5 or 1.4 to 0.5 or 1.3 to 0.5 or 1.2 to 0.5 or 1.1 to 0.5 or 1.0 to 0.5 or 0.9 to 0.5 or 0.8 to 0.5 or 0.7 to 0.5 or 0.6 to 0.5. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.6 or 1.6 to 0.6 or 1.5 to 0.6 or 1.4 to 0.6 or 1.3 to 0.6 or 1.2 to 0.6 or 1.1 to 0.6 or 1.0 to 0.6 or 0.9 to 0.6 or 0.8 to 0.6 or 0.7 to 0.6. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.7 or 1.6 to 0.7 or 1.5 to 0.7 or 1.4 to 0.7 or 1.3 to 0.7 or 1.2 to 0.7 or 1.1 to 0.7 or 1.0 to 0.7 or 0.9 to 0.7 or 0.8 to 0.7. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.8 or 1.6 to 0.8 or 1.5 to 0.8 or 1.4 to 0.8 or 1.3 to 0.8 or 1.2 to 0.8 or 1.1 to 0.8 or 1.0 to 0.8 or 0.9 to 0.8. 
     In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 0.9 or 1.6 to 0.9 or 1.5 to 0.9 or 1.4 to 0.9 or 1.3 to 0.9 or 1.2 to 0.9 or 1.1 to 0.9 or 1.0 to 0.9. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 1.0 or 1.6 to 1.0 or 1.5 to 1.0 or 1.4 to 1.0 or 1.3 to 1.0 or 1.2 to 1.0 or 1.1 to 1.0. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 1.1 or 1.6 to 1.1 or 1.5 to 1.1 or 1.4 to 1.1 or 1.3 to 1.1 or 1.2 to 1.1. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 1.2 or 1.6 to 1.2 or 1.5 to 1.2 or 1.4 to 1.2 or 1.3 to 1.2. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 1.3 or 1.6 to 1.3 or 1.5 to 1.3 or 1.4 to 1.3. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 1.4 or 1.6 to 1.4 or 1.5 to 1.4. In certain embodiments of the present invention, the cis/trans molar ratio ranges from 1.7 to 1.5 or 1.6 to 1.5. In one embodiment of the present invention, the cis/trans molar ratio ranges from 1.7 to 1.6. 
     The processes of this invention may be carried out in the absence or presence of a solvent, e.g., a solvent for the 2,2,4,4-tetraalkylcyclobutane-1,3-dione being hydrogenated which is compatible with the catalyst and the hydrogenation product or products. Examples of such solvents include alcohols such as methanol and ethanol; ethers, such as dimethyl ether and diethyl ether; glycols such as mono-, di- and tri-ethylene glycol; glycol ethers, such as ethylene glycol monobutyl ether and diethylene glycol monobutyl ether; saturated hydrocarbons such as hexane, cyclohexane, octane, and decane; and esters, such as isopropyl isobutyrate, isobutyl propionate, octyl acetate, isobutyl isobutyrate, isobutyl acetate, and the like. In one embodiment, the solvent is isobutyl isobutyrate. In one embodiment, the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is dissolved in the solvent at a concentration of 1 to 60% (w/w), for example 5 to 50%, or 10 to 25%. In one embodiment in which the solvent is isobutyl isobutyrate, the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is dissolved in the solvent at a concentration of 1 to 60% (w/w), for example 5 to 50%, or 10 to 25%. It is often economically advantageous, however, to conduct the process in the absence of solvent and use the neat, molten 2,2,4,4-tetraalkylcyclobutane-1,3-dione alone or as a mixture with the 2,2,4,4-tetraalkylcyclobutane-1,3-diol and other hydrogenation products, including 1-hydroxy-2,2,4-trimethyl-3-pentanone, 3-hydroxy-2,2,4,4, -tetramethylcyclobutane-1-one, and 2,2,4-trimethyl-1,3-pentanediol, as the feed to the process. 
     Another embodiment of the present invention is drawn to a process to produce a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising (1) feeding isobutyric anhydride to a pyrolysis zone to produce a vapor effluent comprising dimethylketene, isobutyric acid, and unreacted isobutyric anhydride; (2) cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor; (3) feeding the dimethylketene vapor to an absorption zone wherein the dimethylketene vapor is dissolved in a solvent comprising an ester containing 4 to 20 carbon atoms and consisting of residues of an aliphatic carboxylic acid and an alkanol to produce an absorption zone effluent comprising a solution of dimethylketene in the solvent; (4) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated to convert dimethylketene to 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and (5) contacting the 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     Another embodiment of the present invention is drawn to a process to produce a 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprising (1) feeding a dialkyl carboxylic acid to a pyrolysis zone wherein the dialkyl carboxylic acid produces a vapor effluent comprising dialkylketene, water, and unreacted dialkyl carboxylic acid; (2) cooling the vapor effluent to condense water and dialkyl carboxylic acid and separating the condensate from the dialkylketene vapor; (3) feeding the dialkylketene vapor to an absorption zone wherein the dialkylketene vapor is dissolved in a solvent comprising an ester containing 4 to 20 carbon atoms and consisting of residues of an aliphatic carboxylic acid and an alkanol to produce an absorption zone effluent comprising a solution of dialkylketene in the solvent; (4) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated to convert dialkylketene to 2,2,4,4-tetraalkylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetraalkylcyclobutane-1,3-dione in the solvent; and (5) contacting the tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The nature of the process for making the dialkylketene is not critical and any conventional method may be used, including, but not limited to, the methods disclosed in U.S. Pat. Nos. 1,602,699, 2,160,841, 2,202,046, 2,278,537, 2,806,064, 3,201,474, 3,259,469, 3,366,689, 3,403,181, 5,475,144 and 6,232,504, all of which are incorporated herein by reference for their disclosure of processes for making a dialkylketene. Processes for the preparation of ketenes, for example, dimethylketene, and cyclobutane-1,3-diones, for example, 2,2,4,4-tetramethylcyclobutane-1,3-dione, may be combined with all aspects of the present invention related to preparation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diols, including mixtures of cis and trans-2,2,4,4-tetraalkylcyclobutane-1,3-diols. 
     All of these novel processes may be carried out as a batch, semi-continuous, or continuous process and may utilize a variety of reactor types. Examples of suitable reactor types include, but are not limited to, stirred tank, continuous stirred tank, slurry, tubular, fixed bed, and trickle bed. The term “continuous” as used herein means a process wherein reactants are introduced and products withdrawn simultaneously in an uninterrupted manner. By “continuous” it is meant that the process is substantially or completely continuous in operation, in contrast to a “batch” process. “Continuous” is not meant in any way to prohibit normal interruptions in the continuity of the process due to, for example, start-up, reactor maintenance, or scheduled shut down periods. The term “batch” process as used herein means a process wherein all the reactants are added to the reactor and then processed according to a predetermined course of reaction during which essentially no material is fed into or removed from the reactor. For example, in a batch operation, a slurry of the catalyst in the cyclobutanedione and/or a solvent in which the cyclobutanedione has been dissolved is fed to a pressure vessel equipped with means for agitation. The pressure vessel is then pressurized with hydrogen to a predetermined pressure followed by heating to bring the reaction mixture to the desired temperature. After the hydrogenation is complete, the reaction mixture is removed from the pressure vessel, the catalyst is separated by filtration, and the 2,2,4,4-tetramethylcyclobutane-1,3-diol product is isolated, for example, in a distillation train or by crystallization. The term “semicontinuous” means a process where some of the reactants are charged at the beginning of the process and the remaining reactants are fed continuously as the reaction progresses. Alternatively, a semicontinuous process may also include a process similar to a batch process in which all the reactants are added at the beginning of the process except that one or more of the products are removed continuously as the reaction progresses. 
     The process may be operated as a continuous process, although semi-continuous and batch processes are within the scope of the invention. Continuous operation may utilize a fixed bed with a larger particle size of catalyst such as, for example, granules, pellets, various multilobal shaped pellets, rings, or saddles that are well known to skilled persons in the art. As an example of a continuous process, the catalyst bed may be fixed in a high pressure, tubular or columnar reactor and the liquid 2,2,4,4-tetraalkylcyclobutane-1,3-dione, dissolved in a solvent if necessary or desired, fed continuously into the top of the bed at elevated pressure and temperature, and the crude hydrogenation product removed from the base of the reactor. Alternatively, it is possible to feed the 2,2,4,4-tetraalkylcyclobutane-1,3-dione into the bottom of the bed and remove the crude product from the top of the reactor. It is also possible to use two or more catalyst beds or hydrogenation zones connected in parallel or in series to improve conversion, to reduce the quantity of catalyst, or to bypass a catalyst bed for periodic maintenance or catalyst removal. Another mode of continuous operation utilizes a slurry of the catalyst in an agitated pressure vessel, which is equipped with a filter leg to permit continuous removal of a solution of product in unreacted 2,2,4,4-tetraalkylcyclobutane-1,3-dione and/or a solvent. In this manner, a liquid reactant or reactant solution can be continuously fed to, and product solution continuously removed from, an agitated pressure vessel containing an agitated slurry of the catalyst. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 8 carbon atoms. 
     In one embodiment, the promoter compound comprises a Group 1 metal compound. In one embodiment, the promoter compound comprises a Group 6 metal compound. In one embodiment, the promoter compound comprises a Group 7 metal compound. In one embodiment, the promoter compound comprises cesium. In one embodiment, the promoter compound comprises chromium. In one embodiment, the promoter compound comprises rhenium. In one embodiment, the promoter compound comprises ruthenium. In one embodiment, the promoter compound comprises cobalt. In one embodiment, the source of the promoter metal is CsNO 3 . In one embodiment, the source of the promoter metal is Cr(NO 3 ) 3 . In one embodiment, the source of the promoter metal is HReO 4 . In one embodiment, the source of the promoter metal is Ru(NO)(NO 3 ) 2 . In one embodiment, the source of the promoter metal is Co(NO 3 ) 2 . 
     In one embodiment, the promoted copper-based catalyst comprises 0.01 to 10 weight percent (wt %) promoter compound, based on the total weight of the promoted copper-based catalyst. In one embodiment, the promoted copper-based catalyst comprises 0.5 to 7 wt % promoter compound. In one embodiment, the promoted copper-based catalyst comprises 1 to 5 wt % promoter compound. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol. In one embodiment, the alkyl radical radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 4 carbon atoms. In one embodiment, the alkyl radical radicals R 1 , R 2 , R 3  and R 4  each are methyl groups. In one embodiment, the 2,2,4,4-tetraalkylcyclobutane-1,3-diol is 2,2,4,4-tetramethylcyclobutane-1,3-diol. In one embodiment, the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is 2,2,4,4-tetramethylcyclobutane-1,3-dione. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 8 carbon atoms and wherein the process further comprises a non-protic solvent. In one embodiment, the non-protic solvent comprises an unsaturated hydrocarbon, a non-cyclic ester, or ether. The term “non-cyclic ester” means the ester is not a lactone, although the alkanol or aliphatic carboxylic acid residues of the ester may have cyclic rings. In one embodiment, the non-cyclic ester contains 4 to 20 carbon atoms and comprises at least one residue of an aliphatic carboxylic acid and at least one residue of an alkanol. In one embodiment, the non-cyclic ester is selected from isopropyl isobutyrate, isobutyl propionate, octyl acetate, isobutyl isobutyrate, isobutyl acetate, and mixtures thereof. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 8 carbon atoms and wherein the process further comprises a protic solvent. In one embodiment, the protic solvent comprises one or more solvents chosen from a monohydric alcohol, a dihydric alcohol, and a polyhydric alcohol. In one embodiment, the protic solvent comprises one or more solvents chosen from a monohydric alcohol and a dihydric alcohol. In one embodiment, the protic solvent comprises methanol or ethylene glycol. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 8 carbon atoms and wherein the promoted copper-based catalyst comprises a support. In one embodiment, the support comprises one or more of silica, alumina, aluminosilicate, silica/alumina, kieselguhr, titania, graphite, silicon carbide, carbon, zirconia, chromate, barium chromate, zinc oxide, clay, and alumina-clay. In one embodiment, the support comprises a form selected from powder, extrudate, spheres, and pellets. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 8 carbon atoms and wherein the pressure ranges from 689 kPa (100 psi) to 41,368 kPa (6000 psi). In one embodiment, the pressure ranges from 1380 kPa (200 psi) to 20,684 kPa (3000 psi). In one embodiment, the pressure ranges from 2068 kPa (300 psi) to 14,789 kPa (2000 psi). In one embodiment, the temperature ranges from 75° C. to 250° C. In one embodiment, the temperature ranges from 120° C. to 200° C. In one embodiment, the temperature ranges from 130° C. to 180° C. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 8 carbon atoms and wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprises cis-2,2,4,4-tetramethylcyclobutane-1,3-diol and trans-2,2,4,4-tetramethylcyclobutane-1,3-diol and the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 to 1.4. In one embodiment, the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 to 1.1. In one embodiment, the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio ranging from 0.5 to 1.1. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each independently have 1 to 8 carbon atoms and wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione, the 2,2,4,4-tetramethylcyclobutane-1,3-diol, or both are in the molten phase. 
     In one embodiment, the present invention provides processes for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol, comprising contacting 2,2,4,4-tetramethylcyclobutane-1,3-dione, a promoted copper-based catalyst, a non-protic solvent, and hydrogen in a hydrogenation zone under conditions of temperature and pressure sufficient to form 2,2,4,4-tetramethylcyclobutane-1,3-diol. In one such embodiment, the 2,2,4,4-tetramethylcyclobutane-1,3-dione and hydrogen are continuously fed into the hydrogenation zone. In one such embodiment, the hydrogenation zone has a temperature ranging from 75° C. to 250° C. In one such embodiment, the pressure ranges from 689 kPa (100 psi) to 41,368 kPa (6000 psi). In one embodiment, the present invention provides processes for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol, comprising contacting 2,2,4,4-tetramethylcyclobutane-1,3-dione, a promoted copper-based catalyst, a non-protic solvent, and hydrogen in a hydrogenation zone under conditions of temperature and pressure sufficient to form 2,2,4,4-tetramethylcyclobutane-1,3-diol, and further comprising continuously recovering an effluent comprising the 2,2,4,4-tetramethylcyclobutane-1,3-diol and the solvent from the hydrogenation zone. In one such embodiment, the process further comprises continuously recycling a portion of the effluent to the hydrogenation zone. In one such embodiment, the process further comprises continuously recovering the effluent from the hydrogenation zone and recovering at least a portion of the 2,2,4,4-tetramethylcyclobutane-1,3-diol from the effluent to form a depleted 2,2,4,4-tetramethylcyclobutane-1,3-diol stream. In one such embodiment, at least a portion of the depleted 2,2,4,4-tetramethylcyclobutane-1,3-diol stream is recycled to the hydrogenation zone. The term “depleted 2,2,4,4-tetramethylcyclobutane-1,3-diol stream” means that the depleted stream has less 2,2,4,4-tetramethylcyclobutane-1,3-diol in it than the effluent from which the depleted stream is derived. In one such embodiment, the hydrogenation zone comprises a tubular, fixed bed, or trickle bed reactor. In one such embodiment, the hydrogenation zone comprises a stirred tank, a continuous stirred tank, or a slurry reactor. In one such embodiment, the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 1.3 or less. In one such embodiment, the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 or more. 
     In one embodiment, the present invention provides processes for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol comprising (1) feeding isobutyric anhydride to a pyrolysis zone, wherein the isobutyric anhydride is heated at a temperature of 350 to 600° C. to produce a vapor effluent comprising dimethylketene, isobutyric acid, and unreacted isobutyric anhydride; (2) cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor; (3) feeding the dimethylketene vapor to an absorption zone, wherein the dimethylketene vapor is contacted with and dissolved in a solvent comprising an ester containing 4 to 20 carbon atoms and consisting of residues of an aliphatic carboxylic acid and an alkanol to produce an absorption zone effluent comprising a solution of dimethylketene in the solvent; (4) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated at a temperature ranging from 70 to 140° C. to convert dimethylketene to 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and (5) contacting the 2,2,4,4-tetramethylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetramethylcyclobutane-1,3-diol. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a ruthenium-promoted copper-based catalyst, the catalyst comprising a silica support, under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each have 1 carbon atom, wherein the temperature ranges from 150° C. to 180° C. or 160° C. to 180° C., wherein the pressure ranges from 34.5 to 100 barg, wherein the cis/trans molar ratio is greater than 0.9, or greater than 0.98 or ranges from 0.9 to 1.06, or ranges from 0.98 to 1.06. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a cesium-promoted copper-based catalyst, the catalyst comprising a silica support, under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each have 1 carbon atom, wherein the temperature ranges from 120° C. to 180° C., or 130° C. to 170° C., or 130° C. to 140° C., or 160° C. to 170° C., or 135° C. to 165° C., wherein the pressure ranges from 34.5 to 100 barg, wherein the conversion of the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is greater than 80%, or greater than 85% or greater than 88%, and wherein the cis/trans molar ratio ranges from 0.38 to 1.26 or from 0.44 to 1.26 or ranges from 1.08 to 1.26. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a chromium-promoted copper-based catalyst, the catalyst comprising zinc oxide support, under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each have 1 carbon atom, wherein the temperature ranges from 120° C. to 180° C. or from 130° C. to 170° C. or from 140° C. to 160° C. or from 135° C. to 165° C., wherein the pressure ranges from 34.5 to 100 barg, wherein the conversion of the 2,2,4,4-tetraalkylcyclobutane-1,3-dione ranges from 90 to 100% and wherein the yield of 2,2,4,4-tetralkylcyclobutane-1,3-diol is greater than 50%. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a cobalt-promoted copper-based catalyst, the catalyst comprising a silica support, under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each have 1 carbon atom, wherein the temperature ranges from 120° C. to 180° C. or from 130° C. to 170° C. or from 140° C. to 160° C. or from 135° C. to 165° C., wherein the pressure ranges from 30 to 40 barg, wherein the conversion of the 2,2,4,4-tetraalkylcyclobutane-1,3-dione ranges from 90 to 100%. 
     In one embodiment, the present invention provides processes for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a ruthenium-promoted copper-based catalyst, the catalyst comprising a barium chromate support, under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, wherein the alkyl radicals R 1 , R 2 , R 3  and R 4  each have 1 carbon atom, wherein the temperature ranges from 150° C. to 180° C. or from 160° C. to 170° C., wherein the pressure ranges from 34.5 to 100 barg, wherein the conversion of the 2,2,4,4-tetraalkylcyclobutane-1,3-dione ranges from 70 to 100%. 
     In one embodiment, the present invention provides processes for making 2,2,4,4-tetramethylcyclobutane-1,3-diol comprising continuously feeding 2,2,4,4-tetramethylcyclobutane-1,3-dione, a non-protic solvent, and hydrogen to a hydrogenation zone comprising a promoted copper-based catalyst at pressure of 689 kPa (100 psi) (7 bar) to 41,368 kPa (6000 psi) (420 bar) and a hydrogenation temperature of 75 to 250° C. and continuously recovering from said hydrogenation zone an effluent comprising 2,2,4,4-tetramethylcyclobutane-1,3-diol and the non-protic solvent. In another embodiment, the process may further comprise continuously recycling a portion of the effluent to the hydrogenation zone. The hydrogenation zone may be any suitable reactor type including, but not limited to, stirred tank, continuous stirred tank, slurry, tubular, fixed bed, and trickle bed. For example, the processes of the invention may be carried out in a trickle bed reactor operated in the liquid phase. Certain embodiments of the invention are further described and illustrated by the following examples. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 
     Further embodiments of the invention include: 
     A process for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, 
     
       
         
         
             
             
         
       
         
         
           
             wherein each of the alkyl radicals R 1 , R 2 , R 3  and R 4  has, independently from each other, 1 to 8 carbon atoms. 
           
         
       
    
     The process according to the embodiment in paragraph 78, further comprising contacting a copper-based catalyst with a promoter to form the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 78-79, wherein the promoted copper-based catalyst comprises a promoter metal chosen from ruthenium, cobalt, a Group 1 metal, a Group 6 metal, and a Group 7 metal. 
     The process according to any of the embodiments in paragraphs 78-80, wherein the promoter comprises a metal chosen from cesium, chromium, rhenium, ruthenium, and cobalt. 
     The process according to any of the embodiments in paragraphs 78-81, further comprising contacting the copper-based catalyst with a promoter in solution to form the promoted copper-based catalyst, wherein the solution of promoter is prepared by dissolving a compound chosen from CsNO 3 , Cr(NO 3 ) 3 , HReO 4 , Ru(NO)(NO 3 ) 2 , and Co(NO 3 ) 2  in a suitable solvent. 
     The process according to any of the embodiments in paragraphs 78-82, wherein the promoted copper-based catalyst comprises 0.01 to 10 weight percent (wt %) promoter metal, based on the total weight of the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 78-83, wherein the promoted copper-based catalyst comprises 0.5 to 7 wt % promoter. 
     The process according to any of the embodiments in paragraphs 78-84, wherein the promoted copper-based catalyst comprises 1 to 5 wt % promoter. 
     The process according to any of the embodiments in paragraphs 78-85, wherein each of the alkyl radical radicals R 1 , R 2 , R 3 , and R 4  has, independently from each other, 1 to 4 carbon atoms. 
     The process according to any of the embodiments in paragraphs 78-86, wherein each alkyl radical R 1 , R 2 , R 3 , and R 4  is a methyl group. 
     The process according to any of the embodiments in paragraphs 78-87, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is 2,2,4,4-tetramethylcyclobutane-1,3-dione. 
     The process according to any of the embodiments in paragraphs 78-88, wherein a non-protic solvent comprising an unsaturated hydrocarbon, a non-cyclic ester, an ether, or a mixture thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 78-89, wherein the non-cyclic ester contains 4 to 20 carbon atoms and comprises at least one residue of an aliphatic carboxylic acid and at least one residue of an alkanol. 
     The process according to any of the embodiments in paragraphs 78-90, wherein the non-cyclic ester is chosen from isopropyl isobutyrate, isobutyl propionate, octyl acetate, isobutyl isobutyrate, isobutyl acetate, and mixtures thereof. 
     The process according to any of the embodiments in paragraphs 78-91, wherein a protic solvent comprising one or more solvents chosen from a monohydric alcohol, a dihydric alcohol, a polyhydric alcohol, and mixtures thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 78-92, wherein the protic solvent comprises methanol, ethylene glycol, or a mixture thereof. 
     The process according to any of the embodiments in paragraphs 78-93, wherein the promoted copper-based catalyst comprises a support, and wherein the support comprises one or more of silica, barium chromate, and zinc oxide. 
     The process according to any of the embodiments in paragraphs 78-94, wherein the support comprises a form chosen from powder, extrudate, spheres, and pellets. 
     The process according to any of the embodiments in paragraphs 78-95, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 78-96, wherein the pressure is from 1380 kPa (200 psi) to 20,684 kPa (3000 psi). 
     The process according to any of the embodiments in paragraphs 78-97, wherein the pressure is from 300 psi to 2000 psi. 
     The process according to any of the embodiments in paragraphs 78-98, wherein the temperature is from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 78-99, wherein the temperature is from 120° C. to 200° C. 
     The process according to any of the embodiments in paragraphs 78-100, wherein the temperature is from 130° C. to 180° C. 
     The process according to any of the embodiments in paragraphs 78-101, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprises cis-2,2,4,4-tetramethylcyclobutane-1,3-diol and trans-2,2,4,4-tetramethylcyclobutane-1,3-diol and the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 to 1.7. 
     The process according to any of the embodiments in paragraphs 78-102, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 to 1.1. 
     The process according to any of the embodiments in paragraphs 78-103, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.4 to 1.1. 
     The process according to any of the embodiments in paragraphs 78-104, wherein the process is a continuous, semi-batch, or batch process. 
     The process according to any of the embodiments in paragraphs 78-105, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione, the 2,2,4,4-tetramethylcyclobutane-1,3-diol, or both are in the liquid phase. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol, comprising contacting 2,2,4,4-tetramethylcyclobutane-1,3-dione, a promoted copper-based catalyst, a non-protic solvent, and hydrogen in a hydrogenation zone under conditions of temperature and pressure sufficient to form 2,2,4,4-tetramethylcyclobutane-1,3-diol. 
     The process according to the embodiment in paragraph 107, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione and hydrogen are continuously fed into the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 107-108, wherein the hydrogenation zone has a temperature from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 107-109, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 107-110, further comprising continuously recovering an effluent comprising the 2,2,4,4-tetramethylcyclobutane-1,3-diol and the solvent from the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 107-111, further comprising continuously recycling a portion of the effluent to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 107-112, further comprising continuously recovering the effluent from the hydrogenation zone and recovering at least a portion of the 2,2,4,4-tetramethylcyclobutane-1,3-diol from the effluent to form a depleted diol stream. 
     The process according to any of the embodiments in paragraphs 107-113, wherein at least a portion of the depleted diol stream is recycled to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 107-114, wherein the hydrogenation zone comprises a tubular reactor, a fixed bed reactor, trickle bed reactor, stirred tank reactor, continuous stirred tank reactor, or slurry reactor. 
     The process according to any of the embodiments in paragraphs 107-115, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 1.3 or less. 
     The process according to any of the embodiments in paragraphs 107-116, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 or more. 
     The process according to any of the embodiments in paragraphs 107-117, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3-1.7. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol comprising:
         (a) feeding isobutyric anhydride to a pyrolysis zone, wherein the isobutyric anhydride is heated at a temperature of 350° C. to 600° C. to produce a vapor effluent comprising dimethylketene, isobutyric acid, and unreacted isobutyric anhydride;   (b) cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor;   (c) feeding the dimethylketene vapor to an absorption zone, wherein the dimethylketene vapor is contacted with a solvent comprising an ester containing 4 to 20 carbon atoms to produce an effluent comprising a solution of dimethylketene in the solvent; wherein the ester comprises residues of an aliphatic carboxylic acid and an alkanol;   (d) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated at a temperature of from 70° C. to 140° C. to convert dimethylketene to 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and   (e) contacting the 2,2,4,4-tetramethylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetramethylcyclobutane-1,3-diol.       

     A process for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, 
     
       
         
         
             
             
         
       
         
         
           
             wherein each of the alkyl radicals R 1 , R 2 , R 3  and R 4  has, independently from each other, 1 to 8 carbon atoms and wherein the promoted copper-based catalyst comprises a silica support. 
           
         
       
    
     The process according to the embodiment in paragraph 120, further comprising contacting a copper-based catalyst with a promoter to form the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 120-121, wherein the promoted copper-based catalyst comprises a promoter metal chosen from cobalt or a Group 1 metal. 
     The process according to any of the embodiments in paragraphs 120-122, wherein the promoter comprises a metal chosen from cesium and cobalt. 
     The process according to any of the embodiments in paragraphs 120-123, further comprising contacting the copper-based catalyst with a promoter in solution to form the promoted copper-based catalyst, wherein the solution of promoter is prepared by dissolving a compound chosen from CsNO 3  and Co(NO 3 ) 2  in a suitable solvent. 
     The process according to any of the embodiments in paragraphs 120-124, wherein the promoted copper-based catalyst comprises 0.01 to 10 weight percent (wt %) promoter metal, based on the total weight of the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 120-125, wherein the promoted copper-based catalyst comprises 0.5 to 7 wt % promoter. 
     The process according to any of the embodiments in paragraphs 120-126, wherein the promoted copper-based catalyst comprises 1 to 5 wt % promoter. 
     The process according to any of the embodiments in paragraphs 120-127, wherein each of the alkyl radical radicals R 1 , R 2 , R 3 , and R 4  has, independently from each other, 1 to 4 carbon atoms. 
     The process according to any of the embodiments in paragraphs 120-128, wherein each alkyl radical R 1 , R 2 , R 3 , and R 4  is a methyl group. 
     The process according to any of the embodiments in paragraphs 120-129, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is 2,2,4,4-tetramethylcyclobutane-1,3-dione. 
     The process according to any of the embodiments in paragraphs 120-130, wherein a non-protic solvent comprising an unsaturated hydrocarbon, a non-cyclic ester, an ether, or a mixture thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 120-131, wherein the non-cyclic ester contains 4 to 20 carbon atoms and comprises at least one residue of an aliphatic carboxylic acid and at least one residue of an alkanol. 
     The process according to any of the embodiments in paragraphs 120-132, wherein the non-cyclic ester is chosen from isopropyl isobutyrate, isobutyl propionate, octyl acetate, isobutyl isobutyrate, isobutyl acetate, and mixtures thereof. 
     The process according to any of the embodiments in paragraphs 120-133, wherein a protic solvent comprising one or more solvents chosen from a monohydric alcohol, a dihydric alcohol, a polyhydric alcohol, and mixtures thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 120-134, wherein the protic solvent comprises methanol, ethylene glycol, or a mixture thereof. 
     The process according to any of the embodiments in paragraphs 120-135, wherein the support comprises a form chosen from powder, extrudate, spheres, and pellets. 
     The process according to any of the embodiments in paragraphs 120-136, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 120-137, wherein the pressure is from 1380 kPa (200 psi) to 20,684 kPa (3000 psi). 
     The process according to any of the embodiments in paragraphs 120-138, wherein the pressure is from 300 psi to 2000 psi. 
     The process according to any of the embodiments in paragraphs 120-139, wherein the temperature is from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 120-140, wherein the temperature is from 120° C. to 200° C. 
     The process according to any of the embodiments in paragraphs 120-141, wherein the temperature is from 130° C. to 180° C. 
     The process according to any of the embodiments in paragraphs 120-142, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprises cis-2,2,4,4-tetramethylcyclobutane-1,3-diol and trans-2,2,4,4-tetramethylcyclobutane-1,3-diol and the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 to 1.3. 
     The process according to any of the embodiments in paragraphs 120-143, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.35 to 1.1. 
     The process according to any of the embodiments in paragraphs 120-144, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.4 to 1.0. 
     The process according to any of the embodiments in paragraphs 120-145, wherein the process is a continuous, semi-batch, or batch process. 
     The process according to any of the embodiments in paragraphs 120-146, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione, the 2,2,4,4-tetramethylcyclobutane-1,3-diol, or both are in the liquid phase. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol, comprising contacting 2,2,4,4-tetramethylcyclobutane-1,3-dione, a promoted copper-based catalyst comprising a silica catalyst, a non-protic solvent, and hydrogen in a hydrogenation zone under conditions of temperature and pressure sufficient to form 2,2,4,4-tetramethylcyclobutane-1,3-diol. 
     The process according to the embodiment in paragraph 148, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione and hydrogen are continuously fed into the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 148-149, wherein the hydrogenation zone has a temperature from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 148-150, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 148-151, further comprising continuously recovering an effluent comprising the 2,2,4,4-tetramethylcyclobutane-1,3-diol and the solvent from the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 148-152, further comprising continuously recycling a portion of the effluent to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 148-153, further comprising continuously recovering the effluent from the hydrogenation zone and recovering at least a portion of the 2,2,4,4-tetramethylcyclobutane-1,3-diol from the effluent to form a depleted diol stream. 
     The process according to any of the embodiments in paragraphs 148-154, wherein at least a portion of the depleted diol stream is recycled to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 148-155, wherein the hydrogenation zone comprises a tubular reactor, a fixed bed reactor, trickle bed reactor, stirred tank reactor, continuous stirred tank reactor, or slurry reactor. 
     The process according to any of the embodiments in paragraphs 148-156, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 1.3 or less. 
     The process according to any of the embodiments in paragraphs 148-157, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 or more. 
     The process according to any of the embodiments in paragraphs 148-158, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3-1.3. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol comprising:
         (a) feeding isobutyric anhydride to a pyrolysis zone, wherein the isobutyric anhydride is heated at a temperature of 350° C. to 600° C. to produce a vapor effluent comprising dimethylketene, isobutyric acid, and unreacted isobutyric anhydride;   (b) cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor;   (c) feeding the dimethylketene vapor to an absorption zone, wherein the dimethylketene vapor is contacted with a solvent comprising an ester containing 4 to 20 carbon atoms to produce an effluent comprising a solution of dimethylketene in the solvent; wherein the ester comprises residues of an aliphatic carboxylic acid and an alkanol;   (d) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated at a temperature of from 70° C. to 140° C. to convert dimethylketene to 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and   (e) contacting the 2,2,4,4-tetramethylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst comprising a silica support under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetramethylcyclobutane-1,3-diol.       

     A process for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, 
     
       
         
         
             
             
         
       
         
         
           
             wherein each of the alkyl radicals R 1 , R 2 , R 3  and R 4  has, independently from each other, 1 to 8 carbon atoms and wherein the promoted copper-based catalyst comprises a zinc oxide support. 
           
         
       
    
     The process according to the embodiment in paragraph 161, further comprising contacting a copper-based catalyst with a promoter to form the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 161-162, wherein the promoted copper-based catalyst comprises a promoter metal chosen from a Group 6 and a Group 7 metal. 
     The process according to any of the embodiments in paragraphs 161-163, wherein the promoter comprises a metal chosen from chromium and rhenium. 
     The process according to any of the embodiments in paragraphs 161-164, further comprising contacting the copper-based catalyst with a promoter in solution to form the promoted copper-based catalyst, wherein the solution of promoter is prepared by dissolving a compound chosen from Cr(NO 3 ) 3  and HReO 4  in a suitable solvent. 
     The process according to any of the embodiments in paragraphs 161-165, wherein the promoted copper-based catalyst comprises 0.01 to 10 weight percent (wt %) promoter metal, based on the total weight of the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 161-166, wherein the promoted copper-based catalyst comprises 0.5 to 7 wt % promoter. 
     The process according to any of the embodiments in paragraphs 161-167, wherein the promoted copper-based catalyst comprises 1 to 5 wt % promoter. 
     The process according to any of the embodiments in paragraphs 161-168, wherein each of the alkyl radical radicals R 1 , R 2 , R 3 , and R 4  has, independently from each other, 1 to 4 carbon atoms. 
     The process according to any of the embodiments in paragraphs 161-169, wherein each alkyl radical R 1 , R 2 , R 3 , and R 4  is a methyl group. 
     The process according to any of the embodiments in paragraphs 161-170, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is 2,2,4,4-tetramethylcyclobutane-1,3-dione. 
     The process according to any of the embodiments in paragraphs 161-171, wherein a non-protic solvent comprising an unsaturated hydrocarbon, a non-cyclic ester, an ether, or a mixture thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 161-172, wherein the non-cyclic ester contains 4 to 20 carbon atoms and comprises at least one residue of an aliphatic carboxylic acid and at least one residue of an alkanol. 
     The process according to any of the embodiments in paragraphs 161-173, wherein the non-cyclic ester is chosen from isopropyl isobutyrate, isobutyl propionate, octyl acetate, isobutyl isobutyrate, isobutyl acetate, and mixtures thereof. 
     The process according to any of the embodiments in paragraphs 161-174, wherein a protic solvent comprising one or more solvents chosen from a monohydric alcohol, a dihydric alcohol, a polyhydric alcohol, and mixtures thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 161-175, wherein the protic solvent comprises methanol, ethylene glycol, or a mixture thereof. 
     The process according to any of the embodiments in paragraphs 161-176, wherein the support comprises a form chosen from powder, extrudate, spheres, and pellets. 
     The process according to any of the embodiments in paragraphs 161-177, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 161-178, wherein the pressure is from 1380 kPa (200 psi) to 20,684 kPa (3000 psi). 
     The process according to any of the embodiments in paragraphs 161-179, wherein the pressure is from 300 psi to 2000 psi. 
     The process according to any of the embodiments in paragraphs 161-180, wherein the temperature is from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 161-181, wherein the temperature is from 120° C. to 200° C. 
     The process according to any of the embodiments in paragraphs 161-182, wherein the temperature is from 130° C. to 180° C. 
     The process according to any of the embodiments in paragraphs 161-183, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprises cis-2,2,4,4-tetramethylcyclobutane-1,3-diol and trans-2,2,4,4-tetramethylcyclobutane-1,3-diol and the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 to 1.7. 
     The process according to any of the embodiments in paragraphs 161-184, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 to 1.1. 
     The process according to any of the embodiments in paragraphs 161-185, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.4 to 1.1. 
     The process according to any of the embodiments in paragraphs 161-186, wherein the process is a continuous, semi-batch, or batch process. 
     The process according to any of the embodiments in paragraphs 161-187, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione, the 2,2,4,4-tetramethylcyclobutane-1,3-diol, or both are in the liquid phase. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol, comprising contacting 2,2,4,4-tetramethylcyclobutane-1,3-dione, a promoted copper-based catalyst comprising a zinc oxide catalyst, a non-protic solvent, and hydrogen in a hydrogenation zone under conditions of temperature and pressure sufficient to form 2,2,4,4-tetramethylcyclobutane-1,3-diol. 
     The process according to the embodiment in paragraph 189, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione and hydrogen are continuously fed into the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 189-190, wherein the hydrogenation zone has a temperature from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 189-191, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 189-192, further comprising continuously recovering an effluent comprising the 2,2,4,4-tetramethylcyclobutane-1,3-diol and the solvent from the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 189-193, further comprising continuously recycling a portion of the effluent to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 189-194, further comprising continuously recovering the effluent from the hydrogenation zone and recovering at least a portion of the 2,2,4,4-tetramethylcyclobutane-1,3-diol from the effluent to form a depleted diol stream. 
     The process according to any of the embodiments in paragraphs 189-195, wherein at least a portion of the depleted diol stream is recycled to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 189-196, wherein the hydrogenation zone comprises a tubular reactor, a fixed bed reactor, trickle bed reactor, stirred tank reactor, continuous stirred tank reactor, or slurry reactor. 
     The process according to any of the embodiments in paragraphs 189-197, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 1.3 or less. 
     The process according to any of the embodiments in paragraphs 189-198, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3 or more. 
     The process according to any of the embodiments in paragraphs 189-199, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.3-1.7. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol comprising:
         (a) feeding isobutyric anhydride to a pyrolysis zone, wherein the isobutyric anhydride is heated at a temperature of 350° C. to 600° C. to produce a vapor effluent comprising dimethylketene, isobutyric acid, and unreacted isobutyric anhydride;   (b) cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor;   (c) feeding the dimethylketene vapor to an absorption zone, wherein the dimethylketene vapor is contacted with a solvent comprising an ester containing 4 to 20 carbon atoms to produce an effluent comprising a solution of dimethylketene in the solvent; wherein the ester comprises residues of an aliphatic carboxylic acid and an alkanol;   (d) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated at a temperature of from 70° C. to 140° C. to convert dimethylketene to 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and   (e) contacting the 2,2,4,4-tetramethylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst comprising a zinc oxide support under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetramethylcyclobutane-1,3-diol.       

     A process for producing a 2,2,4,4-tetraalkylcyclobutane-1,3-diol of Formula II, comprising contacting a 2,2,4,4-tetraalkylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetraalkylcyclobutane-1,3-diol, 
     
       
         
         
             
             
         
       
         
         
           
             wherein each of the alkyl radicals R 1 , R 2 , R 3  and R 4  has, independently from each other, 1 to 8 carbon atoms and wherein the promoted copper-based catalyst comprises a barium chromate support. 
           
         
       
    
     The process according to the embodiment in paragraph 202, further comprising contacting a copper-based catalyst with a promoter to form the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 202-203, wherein the promoter comprises ruthenium. 
     The process according to any of the embodiments in paragraphs 202-204, further comprising contacting the copper-based catalyst with a promoter in solution to form the promoted copper-based catalyst, wherein the solution of promoter is prepared by dissolving Ru(NO)(NO 3 ) 2  in a suitable solvent. 
     The process according to any of the embodiments in paragraphs 202-205, wherein the promoted copper-based catalyst comprises 0.01 to 10 weight percent (wt %) promoter metal, based on the total weight of the promoted copper-based catalyst. 
     The process according to any of the embodiments in paragraphs 202-206, wherein the promoted copper-based catalyst comprises 0.5 to 7 wt % promoter. 
     The process according to any of the embodiments in paragraphs 202-207, wherein the promoted copper-based catalyst comprises 1 to 5 wt % promoter. 
     The process according to any of the embodiments in paragraphs 202-208, wherein each of the alkyl radical radicals R 1 , R 2 , R 3 , and R 4  has, independently from each other, 1 to 4 carbon atoms. 
     The process according to any of the embodiments in paragraphs 202-209, wherein each alkyl radical R 1 , R 2 , R 3 , and R 4  is a methyl group. 
     The process according to any of the embodiments in paragraphs 202-210, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-dione is 2,2,4,4-tetramethylcyclobutane-1,3-dione. 
     The process according to any of the embodiments in paragraphs 202-211, wherein a non-protic solvent comprising an unsaturated hydrocarbon, a non-cyclic ester, an ether, or a mixture thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 202-212, wherein the non-cyclic ester contains 4 to 20 carbon atoms and comprises at least one residue of an aliphatic carboxylic acid and at least one residue of an alkanol. 
     The process according to any of the embodiments in paragraphs 202-213, wherein the non-cyclic ester is chosen from isopropyl isobutyrate, isobutyl propionate, octyl acetate, isobutyl isobutyrate, isobutyl acetate, and mixtures thereof. 
     The process according to any of the embodiments in paragraphs 202-214, wherein a protic solvent comprising one or more solvents chosen from a monohydric alcohol, a dihydric alcohol, a polyhydric alcohol, and mixtures thereof is present during the formation of the 2,2,4,4-tetraalkylcyclobutane-1,3-diol. 
     The process according to any of the embodiments in paragraphs 202-215, wherein the protic solvent comprises methanol, ethylene glycol, or a mixture thereof. 
     The process according to any of the embodiments in paragraphs 202-216, wherein the support comprises a form chosen from powder, extrudate, spheres, and pellets. 
     The process according to any of the embodiments in paragraphs 202-217, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 202-218, wherein the pressure is from 1380 kPa (200 psi) to 20,684 kPa (3000 psi). 
     The process according to any of the embodiments in paragraphs 202-219, wherein the pressure is from 300 psi to 2000 psi. 
     The process according to any of the embodiments in paragraphs 202-220, wherein the temperature is from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 202-221, wherein the temperature is from 120° C. to 200° C. 
     The process according to any of the embodiments in paragraphs 202-222, wherein the temperature is from 130° C. to 180° C. 
     The process according to any of the embodiments in paragraphs 202-223, wherein the 2,2,4,4-tetraalkylcyclobutane-1,3-diol comprises cis-2,2,4,4-tetramethylcyclobutane-1,3-diol and trans-2,2,4,4-tetramethylcyclobutane-1,3-diol and the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.6 to 1.0. 
     The process according to any of the embodiments in paragraphs 202-224, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.7 to 1.0. 
     The process according to any of the embodiments in paragraphs 202-225, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.7 to 0.9. 
     The process according to any of the embodiments in paragraphs 202-226, wherein the process is a continuous, semi-batch, or batch process. 
     The process according to any of the embodiments in paragraphs 202-227, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione, the 2,2,4,4-tetramethylcyclobutane-1,3-diol, or both are in the liquid phase. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol, comprising contacting 2,2,4,4-tetramethylcyclobutane-1,3-dione, a promoted copper-based catalyst comprising a barium chromate catalyst, a non-protic solvent, and hydrogen in a hydrogenation zone under conditions of temperature and pressure sufficient to form 2,2,4,4-tetramethylcyclobutane-1,3-diol. 
     The process according to the embodiment in paragraph 229, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-dione and hydrogen are continuously fed into the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 229-230, wherein the hydrogenation zone has a temperature from 75° C. to 250° C. 
     The process according to any of the embodiments in paragraphs 229-231, wherein the pressure is from 100 psi to 6000 psi. 
     The process according to any of the embodiments in paragraphs 229-232, further comprising continuously recovering an effluent comprising the 2,2,4,4-tetramethylcyclobutane-1,3-diol and the solvent from the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 229-233, further comprising continuously recycling a portion of the effluent to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 229-234, further comprising continuously recovering the effluent from the hydrogenation zone and recovering at least a portion of the 2,2,4,4-tetramethylcyclobutane-1,3-diol from the effluent to form a depleted diol stream. 
     The process according to any of the embodiments in paragraphs 229-235, wherein at least a portion of the depleted diol stream is recycled to the hydrogenation zone. 
     The process according to any of the embodiments in paragraphs 229-236, wherein the hydrogenation zone comprises a tubular reactor, a fixed bed reactor, trickle bed reactor, stirred tank reactor, continuous stirred tank reactor, or slurry reactor. 
     The process according to any of the embodiments in paragraphs 229-237, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.9 or less. 
     The process according to any of the embodiments in paragraphs 229-238, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.7 or more. 
     The process according to any of the embodiments in paragraphs 229-239, wherein the 2,2,4,4-tetramethylcyclobutane-1,3-diol has a cis/trans molar ratio of 0.6-1.0. 
     A process for producing 2,2,4,4-tetramethylcyclobutane-1,3-diol comprising:
         (a) feeding isobutyric anhydride to a pyrolysis zone, wherein the isobutyric anhydride is heated at a temperature of 350° C. to 600° C. to produce a vapor effluent comprising dimethylketene, isobutyric acid, and unreacted isobutyric anhydride;   (b) cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor;   (c) feeding the dimethylketene vapor to an absorption zone, wherein the dimethylketene vapor is contacted with a solvent comprising an ester containing 4 to 20 carbon atoms to produce an effluent comprising a solution of dimethylketene in the solvent; wherein the ester comprises residues of an aliphatic carboxylic acid and an alkanol;   (d) feeding the absorption zone effluent to a dimerization zone wherein the absorption zone effluent is heated at a temperature of from 70° C. to 140° C. to convert dimethylketene to 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce a dimerization zone effluent comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and   (e) contacting the 2,2,4,4-tetramethylcyclobutane-1,3-dione with hydrogen in the presence of a promoted copper-based catalyst comprising a barium chromate support under conditions of temperature and pressure sufficient to form a 2,2,4,4-tetramethylcyclobutane-1,3-diol.       

     EXAMPLES 
     The following examples illustrate in general the processes of the present invention for the production of 2,2,4,4-tetraalkylcyclobutane-1,3-diols by hydrogenation of 2,2,4,4-tetraalkylcyclobutane-1,3-dione. 
     General 
     The following is a general description of the reactor system, catalyst preparation, hydrogenation process, and analytical methods used henceforward in the Examples described below unless otherwise specified. 
     The experiments were performed in a nanoflow parallel fixed bed reactor system under continuous trickle phase conditions in co-current downstream mode utilizing a tubular reactor that has an internal diameter of 2 mm. The reactor is made by Advantium Technologies B.V. The reactor was loaded with solid catalyst to fill a volume of 150 μl. The catalyst was reduced with hydrogen in-situ prior to testing. The catalyst reduction was carried out in the presence of isobutyl isobutyrate at 100 barg (10,000 kPa). Temperature was increased at a rate of 0.5° C./min from ambient temperature to 180° C. and held for 2 hours. All pressures are gauge pressure unless otherwise specified as absolute pressure. The pressures in the tables are in unit of barg unless otherwise specified. 
     The 2,2,4,4-tetramethylcyclobutane-1,3-dione used in the experiments was diluted with isobutyl isobutyrate to a concentration of 10 wt % and heated to 85° C. The 2,2,4,4-tetramethylcyclobutane-1,3-dione/isobutyl isobutyrate feed mixture was fed at the top of the reactor vessel along with hydrogen and contacted with the catalyst. After the system reached the correct process conditions, the system was held at these conditions for 2 hours, which was considered to be the reaction time. The reactor effluent stream containing crude 2,2,4,4-tetramethylcyclobutane-1,3-diol product was removed from the bottom of the reactor. 
     The reactor effluent stream was sampled using a Gilson 233 liquid sampler. 30 μl of the reaction sample was diluted with 970 μl isopropanol and analyzed by capillary gas-liquid chromatography (“GC”) using a TraceGC from Thermo Finnigan with a CombiPal autosampler from CTC Analytics, with a FID detector. The GC samples were injected onto a 0.25 micron (30 m×0.32 mm) Varian CP Wax 52 CB column. For each analysis, the initial temperature of the column was set at 80° C., held for 2 minutes, ramped to 90° C. at a rate of 5° C./min, ramped to 240° C. at a rate of 20° C./min, and then held for 3.5 min at 240° C. Results are given as GC area percentages, normalized for isobutyl isobutyrate. 
     The following abbreviations apply throughout the working examples and tables: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 TMCB 
                 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 Ring-open 
                 1-hydroxy-2,2,4-trimethyl-3-pentanone 
               
               
                 Ketol 
                 (a product of the partial hydrogenation and ring opening of 
               
               
                   
                 2,2,4,4-tetramethylcyclobutane-1,3-dione) 
               
               
                 Cyclic Ketol 
                 3-hydroxy-2,2,4,4-tetramethylcyclobutanone 
               
               
                   
                 (a product of the partial hydrogenation of 2,2,4,4- 
               
               
                   
                 tetramethylcyclobutane-1,3-dione) 
               
               
                 TMPD 
                 2,2,4-trimethyl-1,3-pentanediol 
               
               
                   
                 (a product of the hydrogenation of Ring-opened Ketol) 
               
               
                 Cis-Diol 
                 cis-2,2,4,4-tetramethylcyclobutane-1,3-diol 
               
               
                 Trans-Diol 
                 trans-2,2,4,4-tetramethylcyclobutane-1,3-diol 
               
               
                   
               
            
           
         
       
     
     The conversion, selectivity, and yield of the hydrogenation process as well as the cis:trans ratio of the 2,2,4,4-tetramethylcyclobutane-1,3-diol product were calculated on the basis of GC area percentages using the following formulas: 
     
       
         
           
             
               Conversion 
               ⁢ 
               
                   
               
               ⁢ 
               % 
             
             = 
             
               
                 
                   
                     ( 
                     
                       moles 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       TMCB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       fed 
                     
                     ) 
                   
                   - 
                   
                     ( 
                     
                       moles 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       TMCB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       remaining 
                     
                     ) 
                   
                 
                 
                   ( 
                   
                     moles 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     TMCB 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     fed 
                   
                   ) 
                 
               
               × 
               100 
             
           
         
       
       
         
           
             
               Yield 
               ⁢ 
               
                   
               
               ⁢ 
               % 
             
             = 
             
               
                 
                   
                     ( 
                     
                       
                         moles 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Cis 
                       
                       - 
                       Diol 
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         moles 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Trans 
                       
                       - 
                       Diol 
                     
                     ) 
                   
                 
                 
                   ( 
                   
                     moles 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     TMCB 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     fed 
                   
                   ) 
                 
               
               × 
               100 
             
           
         
       
       
         
           
             Selectivity 
             = 
             
               
                 
                   
                     ( 
                     
                       
                         moles 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Cis 
                       
                       - 
                       Diol 
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         moles 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Trans 
                       
                       - 
                       Diol 
                     
                     ) 
                   
                 
                 
                   
                     ( 
                     
                       moles 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       TMCB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       fed 
                     
                     ) 
                   
                   - 
                   
                     ( 
                     
                       moles 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       TMCB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       remaining 
                     
                     ) 
                   
                 
               
               = 
               
                 Yield 
                 Conversion 
               
             
           
         
       
       
         
           
             
               
                 Cis 
                 / 
                 Trans 
               
               ⁢ 
               
                   
               
               ⁢ 
               Ratio 
             
             = 
             
               
                 ( 
                 
                   
                     moles 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Cis 
                   
                   - 
                   Diol 
                 
                 ) 
               
               
                 ( 
                 
                   
                     moles 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Trans 
                   
                   - 
                   Diol 
                 
                 ) 
               
             
           
         
       
     
     Comparative Example 1 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a copper on silica catalyst from Engelhard Corporation at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The results are shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 using non-promoted copper on silica catalyst. 
               
            
           
           
               
               
               
            
               
                   
                 Comparative Example 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1a 
                 1b 
                 1c 
                 1d 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Metal 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
               
               
                   
                 Promoter 
                 None 
                 none 
                 none 
                 none 
               
               
                   
                 Support 
                 Silica 
                 silica 
                 silica 
                 silica 
               
               
                   
                 Temperature 
                 135 
                 135 
                 165 
                 165 
               
               
                   
                 (° C.) 
               
               
                   
                 Pressure (barg) 
                 34.5 
                 100 
                 34.5 
                 100 
               
               
                   
                 TMCB % 
                 33.6 
                 33.7 
                 34.9 
                 22.8 
               
               
                   
                 Ring-Open 
                 1.7 
                 1.3 
                 9.4 
                 7.8 
               
               
                   
                 Ketol % 
               
               
                   
                 Cyclic Ketol % 
                 51.4 
                 50.1 
                 41.1 
                 41.3 
               
               
                   
                 TMPD % 
                 0 
                 0 
                 0 
                 0 
               
               
                   
                 Cis-Diol % 
                 3.3 
                 3.9 
                 4.3 
                 8.3 
               
               
                   
                 Trans-Diol % 
                 9.6 
                 10.5 
                 10.3 
                 19.8 
               
               
                   
                 Conversion % 
                 65.9 
                 65.8 
                 64.7 
                 76.8 
               
               
                   
                 Selectivity % 
                 12.7 
                 14.3 
                 14.4 
                 27.7 
               
               
                   
                 Yield % 
                 8.4 
                 9.4 
                 9.3 
                 21.3 
               
               
                   
                 Cis/Trans 
                 0.35 
                 0.37 
                 0.42 
                 0.42 
               
               
                   
                   
               
            
           
         
       
     
     Comparative Example 2 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a KL1970-T3 copper on copper on barium chromate catalyst from CRI KataLeuna at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The results are shown in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 using non-promoted KL1970-T3 catalyst. 
               
            
           
           
               
               
            
               
                   
                 Comparative Example 
               
            
           
           
               
               
               
               
               
            
               
                   
                 2a 
                 2b 
                 2c 
                 2d 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Metal 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
               
               
                 Promoter 
                 None 
                 none 
                 none 
                 none 
               
               
                 Support 
                 barium 
                 barium 
                 barium 
                 barium 
               
               
                   
                 chromate 
                 chromate 
                 chromate 
                 chromate 
               
               
                 Temperature 
                 135 
                 135 
                 165 
                 165 
               
               
                 (° C.) 
               
               
                 Pressure (barg) 
                 34.5 
                 100 
                 34.5 
                 100 
               
               
                 TMCB % 
                 2.8 
                 0 
                 0 
                 0 
               
               
                 Ring-Open 
                 2.9 
                 2.8 
                 17.1 
                 7.0 
               
               
                 Ketol % 
               
               
                 Cyclic Ketol % 
                 43.0 
                 24.2 
                 3.0 
                 0.6 
               
               
                 TMPD % 
                 0 
                 0 
                 2.9 
                 6.4 
               
               
                 Cis-Diol % 
                 13.0 
                 18.9 
                 23.3 
                 26.6 
               
               
                 Trans-Diol % 
                 38.3 
                 54.1 
                 53.1 
                 58.8 
               
               
                 Conversion % 
                 97.1 
                 100 
                 100 
                 100 
               
               
                 Selectivity % 
                 50.9 
                 72.8 
                 76.9 
                 86.0 
               
               
                 Yield % 
                 49.4 
                 72.8 
                 76.9 
                 86.0 
               
               
                 Cis/Trans 
                 0.34 
                 0.35 
                 0.44 
                 0.45 
               
               
                   
               
            
           
         
       
     
     Comparative Example 3 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a KL2015-T5 copper on copper on zinc oxide catalyst from CRI KataLeuna at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The results are shown in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 using non-promoted KL2015-T5 catalyst. 
               
            
           
           
               
               
            
               
                   
                 Comparative Example 
               
            
           
           
               
               
               
               
               
            
               
                   
                 3a 
                 3b 
                 3c 
                 3d 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Metal 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
               
               
                 Promoter 
                 None 
                 none 
                 none 
                 none 
               
               
                 Support 
                 zinc oxide 
                 zinc oxide 
                 zinc oxide 
                 zinc oxide 
               
               
                 Temperature 
                 135 
                 135 
                 165 
                 165 
               
               
                 (° C.) 
               
               
                 Pressure (barg) 
                 34.5 
                 100 
                 34.5 
                 100 
               
               
                 TMCB % 
                 67.8 
                 50.0 
                 19.7 
                 0.0 
               
               
                 Ring-Open 
                 4.0 
                 5.8 
                 45.4 
                 13.0 
               
               
                 Ketol % 
               
               
                 Cyclic Ketol % 
                 27.2 
                 40.3 
                 15.6 
                 3.0 
               
               
                 TMPD % 
                 0.0 
                 0.0 
                 12.4 
                 58.5 
               
               
                 Cis-Diol % 
                 0.0 
                 0.9 
                 2.2 
                 8.2 
               
               
                 Trans-Diol % 
                 1.0 
                 2.4 
                 4.6 
                 16.9 
               
               
                 Conversion % 
                 31.8 
                 49.3 
                 79.8 
                 100.0 
               
               
                 Selectivity % 
                 1.0 
                 3.2 
                 6.8 
                 25.4 
               
               
                 Yield % 
                 0.3 
                 1.6 
                 5.5 
                 25.4 
               
               
                 Cis/Trans 
                 0 
                 0.37 
                 0.48 
                 0.48 
               
               
                   
               
            
           
         
       
     
     Example 4 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a cesium-promoted copper on silica catalyst at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The cesium-promoted copper on silica catalyst was prepared from a copper on silica catalyst purchased from Engelhard Corporation as follows: 
     The copper on silica catalyst was ground and sieved, retaining the 0.2-0.4 mm sieve fraction. 500 mg of this fraction of the copper on silica catalyst were wetted with 500 μl of a 1.47 wt % solution of CsNO 3  in water and then dried in air, first at 50° C. for 16 hr and then at 110° C. for 4 hr. After drying, the catalyst was calcined in air by heating from ambient temperature to 400° C. at a rate of 2° C./min, and then maintaining the catalyst at 400° C. for 2 hr. 
     The results of the hydrogenation of TMCB using the cesium-promoted copper catalyst thus prepared are shown in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 using cesium-promoted copper on silica catalyst. 
               
            
           
           
               
               
               
            
               
                   
                 Example 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 4a 
                 4b 
                 4c 
                 4d 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Metal 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
               
               
                 Promoter 
                 Cs 
                 Cs 
                 Cs 
                 Cs 
               
               
                 Support 
                 Silica 
                 silica 
                 silica 
                 silica 
               
               
                 Temperature 
                 135 
                 135 
                 165 
                 165 
               
               
                 (° C.) 
               
               
                 Pressure (barg) 
                 34.5 
                 100 
                 34.5 
                 100 
               
               
                 TMCB % 
                 14.0 
                 11.0 
                 0.0 
                 0.0 
               
               
                 Ring-Open 
                 4.8 
                 0.0 
                 0.0 
                 0.0 
               
               
                 Ketol % 
               
               
                 Cyclic Ketol % 
                 0.0 
                 4.8 
                 0.0 
                 0.0 
               
               
                 TMPD % 
                 0.0 
                 4.0 
                 50.1 
                 34.4 
               
               
                 Cis-Diol % 
                 24.9 
                 22.2 
                 27.8 
                 34.4 
               
               
                 Trans-Diol % 
                 56.3 
                 57.9 
                 22.1 
                 31.5 
               
               
                 Conversion % 
                 85.6 
                 88.7 
                 100 
                 100 
               
               
                 Selectivity % 
                 80.9 
                 79.9 
                 50.2 
                 65.9 
               
               
                 Yield % 
                 69.2 
                 70.9 
                 50.2 
                 65.9 
               
               
                 Cis/Trans 
                 0.44 
                 0.38 
                 1.26 
                 1.08 
               
               
                   
               
            
           
         
       
     
     Example 5 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a cobalt-promoted copper on silica catalyst at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The cobalt-promoted copper on silica catalyst was prepared from a copper on silica catalyst purchased from Engelhard Corporation as follows: 
     The copper on silica catalyst was ground and sieved, retaining the 0.2-0.4 mm sieve fraction. 500 mg of this fraction of the copper on silica catalyst were wetted with 500 μl of a 17.3 wt % solution of Co(NO 3 ) 2 .6H 2 O in water and then dried in air, first at 50° C. for 16 hr and then at 110° C. for 4 hr. After drying, the catalyst was calcined in air by heating from ambient temperature to 400° C. at a rate of 2° C./min, and then maintaining the catalyst at 400° C. for 2 hr. 
     The results of the hydrogenation of TMCB using the cobalt-promoted copper catalyst thus prepared are shown in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 using cobalt-promoted copper on silica catalyst. 
               
            
           
           
               
               
            
               
                   
                 Example 
               
            
           
           
               
               
               
               
            
               
                   
                 5a 
                 5b 
                 5d 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Metal 
                 Cu 
                 Cu 
                 Cu 
               
               
                 Promoter 
                 Co 
                 Co 
                 Co 
               
               
                 Support 
                 Silica 
                 silica 
                 silica 
               
               
                 Temperature (° C.) 
                 135 
                 135 
                 165 
               
               
                 Pressure (barg) 
                 34.5 
                 100 
                 100 
               
               
                 TMCB % 
                 0.0 
                 73.6 
                 53.4 
               
               
                 Ring-Open Ketol % 
                 0.0 
                 0.0 
                 0.0 
               
               
                 Cyclic Ketol % 
                 0.0 
                 26.4 
                 46.6 
               
               
                 TMPD % 
                 0.0 
                 0.0 
                 0.0 
               
               
                 Cis-Diol % 
                 48.3 
                 0.0 
                 0.0 
               
               
                 Trans-Diol % 
                 51.7 
                 0.0 
                 0.0 
               
               
                 Conversion % 
                 100 
                 26.1 
                 46.2 
               
               
                 Selectivity % 
                 100 
                 0.0 
                 0.0 
               
               
                 Yield % 
                 100 
                 0.0 
                 0.0 
               
               
                 Cis/Trans 
                 0.93 
                 not applicable 
                 not applicable 
               
               
                   
               
            
           
         
       
     
     Example 6 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a ruthenium-promoted copper on barium chromate catalyst at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The ruthenium-promoted copper on barium chromate catalyst was prepared from a KL1970-T3 copper on barium chromate catalyst purchased from CRI KataLeuna as follows: 
     The KL1970-T3 catalyst was ground and sieved, retaining the 0.2-0.4 mm sieve fraction. 500 mg of this fraction of the KL1970-T3 catalyst were wetted with 500 μl of a 3.5 wt % solution of Ru(NO)(NO 3 ) 2  in water and then dried in air, first at 50° C. for 16 hr and then at 110° C. for 4 hr. After drying, the catalyst was calcined in air by heating from ambient temperature to 400° C. at a rate of 2° C./min, and then maintaining the catalyst at 400° C. for 2 hr. 
     The results of the hydrogenation of TMCB using the ruthenium-promoted copper catalyst thus prepared are shown in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 using ruthenium-promoted KL1970-T3 copper catalyst. 
               
            
           
           
               
               
            
               
                   
                 Example 
               
            
           
           
               
               
               
               
               
            
               
                   
                 6a 
                 6b 
                 6c 
                 6d 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Metal 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
               
               
                 Promoter 
                 Ru 
                 Ru 
                 Ru 
                 Ru 
               
               
                 Support 
                 barium 
                 barium 
                 barium 
                 barium 
               
               
                   
                 chromate 
                 chromate 
                 chromate 
                 chromate 
               
               
                 Temperature 
                 135 
                 135 
                 165 
                 165 
               
               
                 (° C.) 
               
               
                 Pressure (barg) 
                 34.5 
                 100 
                 34.5 
                 100 
               
               
                 TMCB % 
                 92.3 
                 83.8 
                 26.7 
                 1.8 
               
               
                 Ring-Open 
                 0.0 
                 0.0 
                 6.4 
                 9.0 
               
               
                 Ketol % 
               
               
                 Cyclic Ketol % 
                 7.3 
                 15.7 
                 62.4 
                 64.6 
               
               
                 TMPD % 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
               
               
                 Cis-Diol % 
                 0.0 
                 0.0 
                 1.9 
                 10.8 
               
               
                 Trans-Diol % 
                 0.0 
                 0.0 
                 2.6 
                 12.7 
               
               
                 Conversion % 
                 7.3 
                 15.6 
                 73.0 
                 98.1 
               
               
                 Selectivity % 
                 0.0 
                 0.0 
                 4.5 
                 23.5 
               
               
                 Yield % 
                 0.0 
                 0.0 
                 3.3 
                 23.1 
               
               
                 Cis/Trans 
                 not applicable 
                 not applicable 
                 0.74 
                 0.85 
               
               
                   
               
            
           
         
       
     
     Example 7 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a rhenium-promoted copper on zinc oxide catalyst at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The rhenium-promoted copper on zinc oxide catalyst was prepared from a KL2015-T5 copper on zinc oxide catalyst purchased from CRI KataLeuna as follows: 
     The KL2015-T5 catalyst was ground and sieved, retaining the 0.2-0.4 mm sieve fraction. 500 mg of this fraction of the KL2015-T5 catalyst were wetted with 500 μl of a 75 wt % solution of HReO 4  in water and then dried in air, first at 50° C. for 16 hr and then at 110° C. for 4 hr. After drying, the catalyst was calcined in air by heating from ambient temperature to 400° C. at a rate of 2° C./min, and then maintaining the catalyst at 400° C. for 2 hr. 
     The results of the hydrogenation of TMCB using the rhenium-promoted copper catalyst thus prepared are shown in Table 7. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione 
               
               
                 using rhenium-promoted KL2015-T5 copper catalyst. 
               
            
           
           
               
               
            
               
                   
                 Example 
               
            
           
           
               
               
               
               
               
            
               
                   
                 7a 
                 7b 
                 7c 
                 7d 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Metal 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
               
               
                 Promoter 
                 Re 
                 Re 
                 Re 
                 Re 
               
               
                 Support 
                 zinc oxide 
                 zinc oxide 
                 zinc oxide 
                 zinc oxide 
               
               
                 Temperature 
                 135 
                 135 
                 165 
                 165 
               
               
                 (° C.) 
               
               
                 Pressure (barg) 
                 34.5 
                 100 
                 34.5 
                 100 
               
               
                 TMCB % 
                 4.0 
                 0.0 
                 0.0 
                 0.6 
               
               
                 Ring-Open 
                 21.5 
                 25.7 
                 76.6 
                 59.9 
               
               
                 Ketol % 
               
               
                 Cyclic Ketol % 
                 68.2 
                 33.2 
                 20.9 
                 2.5 
               
               
                 TMPD % 
                 0.0 
                 0.0 
                 0.0 
                 3.6 
               
               
                 Cis-Diol % 
                 3.2 
                 20.8 
                 0.0 
                 16.7 
               
               
                 Trans-Diol % 
                 3.0 
                 20.3 
                 2.5 
                 16.0 
               
               
                 Conversion % 
                 95.9 
                 100 
                 100 
                 99.4 
               
               
                 Selectivity % 
                 6.2 
                 40.9 
                 2.5 
                 33.0 
               
               
                 Yield % 
                 5.9 
                 40.9 
                 2.5 
                 32.8 
               
               
                 Cis/Trans 
                 1.04 
                 1.03 
                 0 
                 1.04 
               
               
                   
               
            
           
         
       
     
     Example 8 
     Using the general procedure described above, 2,2,4,4-tetramethylcyclobutane-1,3-dione was hydrogenated using a chromium-promoted copper on zinc oxide catalyst at temperatures of 135° C. and 165° C., reactor pressures of 34.5 barg (3450 kPa) and 100 barg (10,000 kPa), and a liquid space velocity of 25 hr −1 . The chromium-promoted copper on zinc oxide catalyst was prepared from a KL2015-T5 copper on zinc oxide catalyst purchased from CRI KataLeuna as follows: 
     The KL2015-T5 catalyst was ground and sieved, retaining the 0.2-0.4 mm sieve fraction. 500 mg of this fraction of the KL2015-T5 catalyst were wetted with 500 μl of a 26.9 wt % solution of Cr(NO 3 ) 3 .9H 2 O in water and then dried in air, first at 50° C. for 16 hr and then at 110° C. for 4 hr. After drying, the catalyst was calcined in air by heating from ambient temperature to 400° C. at a rate of 2° C./min, and then maintaining the catalyst at 400° C. for 2 hr. 
     The results of the hydrogenation of TMCB using the chromium-promoted copper catalyst thus prepared are shown in Table 8. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione using 
               
               
                 chromium-promoted KL2015-T5 copper catalyst. 
               
            
           
           
               
               
            
               
                   
                 Example 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 8a 
                 8b 
                 8c 
                 8d 
                 8e 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Metal 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
                 Cu 
               
               
                 Promoter 
                 Cr 
                 Cr 
                 Cr 
                 Cr 
                 Cr 
               
               
                 Support 
                 zinc oxide 
                 zinc oxide 
                 zinc oxide 
                 zinc oxide 
                 zinc 
               
               
                   
                   
                   
                   
                   
                 oxide 
               
               
                 Temperature 
                 135 
                 135 
                 135 
                 135 
                 165 
               
               
                 (° C.) 
               
               
                 Pressure (barg) 
                 34.5 
                 34.5 
                 100 
                 100 
                 100 
               
               
                 TMCB % 
                 0.0 
                 0.0 
                 0.0 
                 1.1 
                 10.2 
               
               
                 Ring-Open 
                 17.3 
                 15.2 
                 3.5 
                 0.0 
                 0.0 
               
               
                 Ketol % 
               
               
                 Cyclic Ketol % 
                 0.0 
                 0.9 
                 0.0 
                 0.0 
                 0.0 
               
               
                 TMPD % 
                 25.2 
                 30.0 
                 29.1 
                 36.2 
                 75.8 
               
               
                 Cis-Diol % 
                 15.6 
                 14.7 
                 18.9 
                 18.4 
                 8.7 
               
               
                 Trans-Diol % 
                 41.9 
                 39.2 
                 48.5 
                 44.3 
                 5.2 
               
               
                 Conversion % 
                 100 
                 100 
                 100 
                 98.8 
                 89.4 
               
               
                 Selectivity % 
                 57.7 
                 54.1 
                 67.7 
                 62.9 
                 14.1 
               
               
                 Yield % 
                 57.7 
                 54.1 
                 67.7 
                 62.2 
                 12.6 
               
               
                 Cis/Trans 
                 0.37 
                 0.37 
                 0.39 
                 0.41 
                 1.67