Abstract:
A de-alkylation process which comprises contacting a t-alkylether-alkanol, e.g. 4-t-butylether-n-butan-1-ol, with an acidic solid mixed oxide, e.g. silica-alumina, catalyst which results in the formation of alkanediols, e.g. 1,4-butanediol, in the substantial absence of undesirable side reactions, e.g. the formation of tetrahydrofuran. The resulting alkanediols are useful in the preparation of polyesters, e.g. polybutylene terephthalates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This invention is related to W. E. Smith&#39;s U.S. Application Ser. No. 189,190 filed Sept. 22, 1980, a continuation-in-part of U.S. Ser. No. 105,876, filed Dec. 20, 1979, now abandoned, which describes the use of an acidic zinc halide catalyst in a t-alkylether-alkanol de-alkylation process. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the use of a solid acidic mixed oxide catalyst to enhance a process which converts t-alkylether-alkanols to alkanediols in the substantial absence of undesirable cyclic ether by-products. 
     2. Description of the Prior Art 
     The de-alkylation of certain t-alkylether-alkanols such as 4-t-butylether-n-butan-1-ol to form alkanediols, such as 1,4-butanediol employing acidic catalysts, such as aqueous phosphoric acid or sulfuric acid, as well as acid ion exchange resins at temperatures of about 100° C. has been reported. 
     The dehydration of certain alkanediols such as 1,4-butanediol to form cyclic ethers, such as tetrahydrofuran employing strong acid catalysts such as phosphoric acid, acidic clays, acidic alumina at temperatures of about 120° C. has also been reported. 
     DESCRIPTION OF THE INVENTION 
     The process of this invention comprises contacting a solid acidic mixed oxide catalyst and a 4-t-alkylether-alkan-1-ol to selectively form alkan-1,4-diols in the substantial absence of cyclic ethers. 
     The t-alkylether-alkanols are defined by the formula: ##STR1## wherein R 1  and R 2  each, independently of the other, represents a C 1  to C 4  alkyl radical, and R 3  and R 4  each, independently of the other, represents a hydrogen atom or a C 1  to C 3  alkyl radical, or wherein R 1  represents a C 1  to C 4  alkyl radical, R 2  and R 3  together with the carbon atoms to which they are attached form a 5-membered or 6-membered cycloaliphatic ring, and C 4  represents a hydrogen atom or a C 1  to C 3  alkyl radical. 
     The reaction conditions of this process promote the formation (k 1 ) of alkanediols and alkenes while limiting the formation of cyclic ethers, i.e. (k 2 ). ##STR2## wherein R 1 , R 2 , R 3  and R 4  are the same as defined herein before. 
     The solid acidic mixed oxide catalysts include any solid acidic silica-alumina composition, e.g. any solid acidic oxide mixture of silica and alumina, i.e. SiO 2 .Al 2  O 3 . The oxides of silica and alumina can be present in any proportion. Illustratively, the weight percent of presently preferred SiO 2 .Al 2  O 3  mixed oxides are within the range of from about 90:10 to about 70:30. 
     Surface area parameters of the mixed oxides measured in square meters per gram (m 2  /g) are not critical to the efficacy of the process. Generally effective SiO 2 .Al 2  O 3  surface areas are within the range of from about 50 to about 400 m 2  /g. 
     Temperature parameters relative to optimum conversion of t-alkylether-alkanol to alkanediol without the formation of cyclic ethers are temperatures within the range of from about 100°-140°, preferably from about 125° to 135° C. 
     Pressure parameters are not critical to the efficacy of the process. Accordingly the process can be carried out under widely varying pressures, e.g. sub-, super- or atmospheric pressures. 
     In a presently preferred embodiment of this process where 4-t-butylether-n-butan-1-ol is de-alkylated to form 1,4-butanediol at least 60, preferably about 75-80, mole percent of 4-t-butylether-n-butan-1-ol is de-alkylated to form 1,4-butanediol while the minimum ultimate selectivity of the process provides a butanediol-tetrahydrofuran product selectivity (Sel.) of at least about 95 percent based upon the following calculation. 
    
    
     Examples I-IV illustrate the best mode of practicing this invention. 
     FIRST GENERAL PROCEDURE 
     A series of de-alkylation reactions were carried out involving the conversion of 4-t-butylether-n-butan-1-ol to 1,4butanediol using a solid acidic SiO 2 .Al 2  O 3  catalyst. 4.0 Grams 98+% of 4-t-butylether-n-butan-1-ol and 0.2 grams of SiO 2 .Al 2  O 3  blanketed with N 2  were heated in a 25 ml flask fitted with a reflux condenser and a magnetic stirrer. The evolved gas isobutylene containing some entrained THF and/or t-butanol, escaping from the reflux condenser was collected at -78° C. and quantified by standard vacuum line techniques at the conclusion of the reaction. 
     The liquid phase reaction product constituents were monitored employing standard G.P.C. techniques throughout the course of the reactions. The mass balance of liquid and gasous products of Examples I-IV was within the range of from 95-99%. A summary of the liquid phase reaction medium constitutes, e.g. tetrahydrofuran (THF), t-butanol, 1,4-di-t-butoxybutane, 4-t-butylether-n-butan-1-ol, and 1,4-butanediol correlated with elapsed reaction time period is reported in Tables I-IV. 
     
                                           TABLE 1__________________________________________________________________________EXAMPLE I__________________________________________________________________________Silica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-ol at 120° C.          1,4-di-t-                  4-t-butylether-n-Time/hrTHF.sup.2    t-butanol.sup.2          butoxybutane.sup.2                  butan-1-ol.sup.2                          1,4-butanediol.sup.2                                  Av Rate.sup.3                                       Selectivity.sup.4                                             Conversion.sup.5__________________________________________________________________________1    .95 1.05  5.3     63.4    29.2    39.7 --    29.22    .67 .73   5.6     52.6    40.4    27.4 --    40.43    .38 .42   4.7     46.4    48.0    21.9 --    48.04    .52 .60   3.7     36.9    58.2    19.9 --    58.25.5  .95 1.05  3.1     28.8    66.1    16.4 98.6  66.1__________________________________________________________________________ .sup.1 GraceDavison grade 98025 silicaalumina pellets crushed to a fine powder. Typical analysis of commercial Davidson siliconalumina is set out hereafter in Example I  Table 1 Addendum. .sup.2 Mole percent. .sup.3 Av Rate = moles of 4t-butylether-n-butan-1-ol converted to 1,4butanediol/kg cat. × total elapsed reaction time period. ##STR3## *NOTE: selectivity values at interim time periods are not reported since any THF contained in condensed isobutylene gas was only analyzed at conclusion of run.) ##STR4## -  - 
    
     
         AddendumGrace-Davison - SiO.sub.2 · Al.sub.2 O.sub.3 Typical AnalysisGrade                    980-25__________________________________________________________________________CHEMICAL PROPERTIES                    2.5Silica, SiO.sub.2        74.5Alumina, Al.sub.2 O.sub.3                    25.0Sodium, Na.sub.2 O       0.05Sulfate, SO.sub.4        0.30Iron, Fe                 0.03Calcium, CaO             0.05Chlorine, Cl             &lt;.01PHYSICALSurface Area, m.sup.2 /gm                    325Pore Volume, cc/gm       0.45Packed Density, gm/cc    0.73Avg. Crush Strength, lbs.                    15(3/16&#34;)__________________________________________________________________________ 
    
     Examples V-XI including the Second General Procedure illustrate attempts to de-alkylate--in the presence of other acidic substances--tertiary alkylether-alkanols. These examples are not a part of this invention and are furnished for the purpose of contrasting the efficacy of the acidic materials used as catalyst candidates with the efficacy of the silicaalumina catalysts used in Examples I-IV. 
     SECOND GENERAL PROCEDURE 
     A series of de-alkylation reactions were tried involving attempts to convert 4-t-butylether-n-butan-1-ol to 1,4-butanediol using other acidic candidates, e.g. SiO 2 , Al 2  O 3 , MgO, WO 3 .Al 2  O 3 , Acidic Clay, Acid Ion Exchange Resin, and Aqueous H 3  PO 4  catalyst. 8.6 grams--except in Example IX where 6.0 grams was used--of a mixture containing, on a mole percent basis, 4-t-butylether-n-butan-1-ol and 3-t-butylether-2-methylpropan-1-ol plus 0.20 grams of a catalyst candidate were blanketed with N 2  and heated in a 25 ml flask fitted with a reflux condenser and a magnetic stirrer. The liquid phase reaction product constituents were monitored employing standard V.P.C. techniques throughout the course of the reactions. A summary of the liquid phase reaction medium constituents, e.g. tetrahydrofuran (THF), 3-t-butylether-2-methyl-propan-1-ol, 2-methyl-1,3-propanediol, 4-t-butylether-n-butan-1-ol, and 1,4-butanediol correlated with elapsed reaction time period is reported in Examples V-XI. 
     
                                           TABLE 2__________________________________________________________________________EXAMPLE IISilica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-ol at 125° C.          1,4-di-t-                  4-t-butylether-n-Time/hrTHF.sup.2    t-butanol.sup.2          butoxybutane.sup.2                  butan-1-ol.sup.2                          1,4-butanediol.sup.2                                  Av Rate.sup.3                                        Selectivity.sup.4                                              Conversion.sup.5__________________________________________________________________________1    .52 1.6   6.3     54.9    36.6    50.1  --    36.62    .67 1.5   4.5     36.6    56.7    38.8  --    56.73    .55 1.2   4.2     31.4    62.6    28.6  --    62.64    .48 1.2   3.3     25.4    69.7    23.9  98.5.sup.6                                              69.7__________________________________________________________________________ Footnotes .sup.1, .sup.2, .sup.3, .sup.4 and .sup.5 = same as in Example  Table 1. .sup.6 = total THF 0.48 (lig. phase) + 0.57 (gas phase) = 1.05 mole % 
    
     
                                           TABLE 3__________________________________________________________________________EXAMPLE IIISilica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-ol at 130° C.Time/hrTHR.sup.2    1,4-di-t-butoxybutane.sup.2               4-t-butylether-n-butan-1-ol                            1,4-butanediol                                   Av Rate.sup.3                                        Selectivity.sup.4                                              Conversion.sup.5__________________________________________________________________________1    1.2 5.0        40.9         53.4   73.1 --    53.42    1.7 3.1        26.9         68.3   46.7 --    68.33    2.0 1.7        19.0         77.3   35.3 --    77.34    2.4 0.7        11.8         85.1   29.1 --    85.15.5  0.5 0.6        11.4         87.5   21.7 97.2.sup.6                                              87.5__________________________________________________________________________ Footnotes .sup.1, .sup.2, .sup.3, .sup.4, and .sup.5 = same as Example I Table 1. .sup.6 = total THF 0.5 (lig. phase) + 2.0 (gas phase) = 2.5 mole % 
    
     
                                           TABLE 4__________________________________________________________________________EXAMPLE IVSilica-Alumina.sup.1 Catalyzed De-alkylation of 4-t-butylether-n-butan-1-ol at 135° C.Time/hrTHF.sup.2    1,4-di-t-butoxybutane.sup.2               4-t-butylether-n-butan-1-ol.sup.2                            1,4-butanediol.sup.2                                   Av Rate.sup.3                                        Selectivity.sup.4                                              Conversion.sup.5__________________________________________________________________________0.5  0.7 5.9        49.9         43.5   119.2                                        --    43.51.0  0.9 4.4        39.3         60.5   82.9 --    60.51.5  2.4 3.5        27.7         66.4   60.6 --    66.42.0  2.0 2.4        22.4         73.2   50.1 --    73.23.0  2.6 1.1        12.0         84.3   38.5 95.4.sup.6                                               84.23__________________________________________________________________________ Footnotes .sup.1, .sup.2, .sup.3, .sup.4, and .sup.5 = same as Example I Table 1. .sup.6 = total THF 2.6 (lig. phase) + 2.5 (gas phase) = 4.1 mole % 
    
     
                                           TABLE 5__________________________________________________________________________EXAMPLES V-XIAttempted Acid Catalyzed De-alkylation of Tertiary-Alkylether-Alkanols                     3-t-          4-t-                     butylether-   butylether-  1,4-  Con-Ex. Catalyst      Temperature             Time/   2-methyl-                            2-methyl-1,3-                                   n-     1,4-  butanediol                                                      ver-No. Candidate      Range  hr  THF.sup.1                     propan-1-ol.sup.1                            propanediol.sup.1                                   butan-1-ol.sup.1                                          butanediol.sup.1                                                Selectivity.sup.2                                                      sion.sup.3__________________________________________________________________________V   SiO.sub.2      190°-192° C.             0   --  13.8   --     81.7   --    --    --             2.5 0   13.8   0      81.7   0     --    --VI  Al.sub.2 O.sub.3      172°-175° C.             0   --  13.8   --     81.7   --    --    --             5.5  1.3                     13.8   trace  78.6   trace n.d..sup.4                                                      traceVII MgO    192°-195° C.             0   0   16.2   --     74.2   --    --    --             3   trace                     16.2   trace  74.2   trace n.d..sup.4                                                      traceVIII    WO.sub.3 . Al.sub.2 O.sub.3      171°  C.             --  --  16.2   --     74.2   --    --    --             4.5 trace                     15.3   0.92   70.6   3.60  n.d..sup.4                                                      traceIX  Acidic  95° C.             0   --  13.9   --     86.1   --    --    --    Clay          6.5  9.8                     0.15   14.2    0.9   75.1  88.5  87.2X   Acid Ion      0   --  13.6   --     86.4   --    --    --    Exchange      95° C.             9   30.5                     6.4    8.2    24.1   30.8  50.2  35.7    ResinXI  Aq . H.sub.3 PO.sub.4      145° C.             0   --  13.6   --     86.4   --    --    --             5   12.1                     0.1    12.9    0.4   74.5  86.0  86.2__________________________________________________________________________ .sup.1 Mole percent. ##STR5## ##STR6## *(NOTE no analysis of isobutylene effluent for trace amounts of other constituents.) 
    
     A brief description of the catalyst candidates of Examples V-X including their commercial sources, is set out in the following Table 5 Addendum: 
     
         __________________________________________________________________________ExampleNo.               Catalyst Candidate Description - Table 5__________________________________________________________________________             AddendumV    SiO.sub.2    J.T. Baker Co. - Silicic Acid, 88% SiO.sub.2 . 12%             H.sub.2 OVI   Al.sub.2 O.sub.3             Alcoa-Activated AluminaVII  MgO          Fisher-Magnesium Oxide, Certified Reagent GradeVIII WO.sub.3 . Al.sub.2 O.sub.3             Harshaw Tungsten Oxide-W-0801 90% WO.sub.3 . 10%             Al.sub.2 O.sub.3IX   Acidic Clay  Girdler KSF Montmorillonite Clay - a natural             SiO.sub.2 . Al.sub.2 O.sub.3 clay treated with H.sub.2             SO.sub.4X    Acid Ion Exchange Resin             Dow Chemical Co. Dowex(TM) 50WX8 a strong-             ly acidic sulfonated polystyrene resin__________________________________________________________________________ 
    
     In general, the utility of this process provides for the de-alkylation of a tertiary-alkylether-alkanol of Formula (I) to form 1,4-alkanediols while at least 60, preferably 75-80, mole percent of tertiary-alkylether-alkanol is de-alkylated to form 1,4-alkanediols while the minimum ultimate selectivity of the process provides a 1,4-alkanediol/1,4-alkanediol plus cyclic ether product selectivity of at least about 95 percent. 
     The expression tertiary-alkylether-alkanol as used herein generically describes aliphatic and cycloaliphatic hydroxyethers commonly referred to as tertiary-alkoxy-alkanols, tertiary-cycloalkoxy-alkanols and tertiary-alkcycloalkoxy-alkanols. Illustratively as used herein the expressions: 
     tertiary-alkylether-alkanol also means tertiary-alkoxy-alkanol 
     4-t-butylether-n-butan-1-ol also means 4-t-butoxy-n-butan-1-ol 
     3-t-butylether-2-methyl-propan-1-ol also means 3-t-butoxy-2-methylpropan-1-ol 
     Accordingly, as will be apparent to those skilled in the art, either of the above forms of chemical nomenclature can be used interchangeably throughout the specification as well as the claims.