Abstract:
Production of bis-(alpha-alkylbenzyl)ethers or substituted derivatives thereof by reaction at elevated temperature of the corresponding alpha alkylbenzyl alcohols in the presence of a mineral acid treated calcined alumina catalyst, quenching the catalyst with a basic compound and recovery of the desired ether by distillation following separation of the quenched catalyst, is disclosed. The alkyl methylbenzyl alcohol may be present as a component of an aromatic rich distill and product mixture derived from the ethyl benzene hydroperoxide epoxidation of an olefinically unsaturated compound.

Description:
FIELD OF THE INVENTION 
     This invention relates to a process for the production of bis(alpha-alkylbenzyl)ethers, such as bis(alpha-methylbenzyl)ether, by heating an alpha-alkyl benzyl alcohol, illustratively, alpha-methylbenzyl alcohol, (&#34;MBA&#34;), in the presence of a mineral acid treated calcined alumina catalyst. The present application is especially concerned with the use of the specified catalysts in the etherification of an alpha methylbenzyl alcohol which is produced as a component of an epoxidation reaction product mixture obtained from the process for the production of an oxirane compound by the oxidation of ethylbenzene to produce an ethylbenzene hydroperoxide product mixture, followed by epoxidation of an olefinically unsaturated compound with said ethylbenzene hydroperoxide product mixture. 
     DESCRIPTION OF THE PRIOR ART AND BACKGROUND OF THE INVENTION 
     Bis(alpha-alkylbenzyl)ethers, such as bis(alphamethylbenzyl)ether, have found application as dye carriers in the fabric industry, solvents in copying paper, and as direct substitutes for polychlorinated biphenyls in capacitors, and as heat transfer media, as well as components for use in the fragrance field. Certain of such ethers have also found use as pesticides, antioxidants, plastic additives and germicides. For example, Japanese Pat. No. 79-149900 has recently referred to the use of such ethers as electrical insulating oils and Japanese Pat. No. 79-136915 has referred to the use of such ethers in pressure-sensitive copying papers. The preparation of bis-(alpha-alkylbenzyl)ethers by reaction of a suitable alpha-unsubstituted or substituted phenyl-alkanol in the presence of a dehydrating agent, such as sulfuric acid, benzene-sulfonic acid, toluenesulfonic acid, and camphorsulfonic acid, thereby splitting out water and forming an ether linkage between the aliphatic carbon atoms of two molecules of the original alkanol compound has been reported in the literature, for example, in U.S. Pat. No. 2,366,203 and Journal of Organic Chemistry, 28, 2914-5 (1963). More recently, as is disclosed in U.S. Pat. No. 4,299,996, a specific class of ion exchange resins containing acidic functionalities has been suggested for use in the preparation of aryl-alkyl ethers from the corresponding alkanols. Another conventional process for the preparation of bis ethers, such as alpha-methylbenzyl alcohol involves reaction of alpha-methylbenzyl chloride with the sodium salt of alpha-methylbenzyl alcohol. However, these processes suffer a combination of shortcomings, including poor selectivity to the desired bis ether, poor reproducibility of results, generation of large amounts of waste and high costs. 
     Acid treatment is known to improve the properties of particulate, alumina-containing amorphous oxides for various uses such as absorption and as catalyst binders or supports. Treatment of alumina with acids will usually dissolve alumina in the acid phase and increase porosity and permeability and lower bulk density of the acid treated material. For example, U.S. Pat. No. 3,836,561 teaches that loss in structural stability caused by acid treatment of alumina containing amorphous refractory oxides is minimized by reacting the oxide with an acid in an aqueous medium at pH below about 5 in the presence of an ionizable salt soluble in the aqueous phase under conditions of temperature, pH and reaction time correlated with the reactivity of the acid and the oxide sufficient to react a portion of the alumina with the acid. 
     U.S. Pat. No. 3,997,476 discloses a process for increasing the pore volume of alumina by treating a calcined alumina with an organic acid, separating the acid-treated alumina from the acid solution by filtration or decantation, washing and drying the separated alumina in air or in a vacuum oven, and calcining the dried alumina at a temperature ranging from about 450° to about 550° C. for a period of time ranging from about 1 to 16 hours. 
     The refining of alpha-alkylbenzyl ethers, such as alpha-methylbenzyl ether, by distillation, such as azeotropic distillation, has also been reported in U.S. Pat. No. 2,927,064. 
     In one prior process for producing alkylene oxides, e.g. propylene oxide and styrene monomer, ethylbenzene is oxidized with air in a series of oxidizers to yield a solution of ethylbenzene hydroperoxide in ethylbenzene. During this oxidation, substantial quantities of methylbenzyl alcohol and acetophenone by-products are formed. This solution of ethylbenzene hydroperoxide is then concentrated in successive steps of distillation, and unreacted ethylbenzene is recycled for oxidation. In this process, ethylbenzene hydroperoxide is then typically used to epoxidize the olefinically unsaturated compound e.g. propylene, to propylene oxide, in the presence of a suitable catalyst, and the hydroperoxide itself is converted to methylbenzyl alcohol. By-products of this reaction include additional quantities of acetophenone, phenol, benzaldehyde, 2-phenylethanol, unreacted reactants and high boiling materials. 
     Excess propylene in the aforementioned propylene oxide epoxidation product is normally removed by distillation and propylene oxide may then be recovered by distillation as a crude product, leaving a stream comprising excess ethylbenzene, the aforementioned by-products and residues. The stream is then distilled to recover ethylbenzene overheads, leaving an aromatic rich distilland comprising methylbenzyl alcohol, acetophenone and a variety of other by-products, including aromatic alcohols. The composition of such distilland may vary widely and comprises a variety of alcohols, ketones and other by-products, as set forth in Table I, below. 
     In a typical propylene-oxide styrene monomer production process, the aforementioned methylbenzyl alcohol/acetophenone distilland (bottom stream) is purified through distillation, and then is fed through styrene production reactors where it is contacted in a liquid phase with a suitable dehydration catalyst to convert methylbenzyl alcohol to styrene. After removing styrene from the dehydration reaction product by distillation, there is produced an acetophenone-rich bottoms product which is then hydrogenated using a suitable catalyst to convert acetophenone to methylbenzyl alcohol, which may then be recycled for styrene production or employed in alternative applications. Further information concerning the production of alpha-methylbenzyl alcohol from such processes is described in U.S. Pat. No. 3,403,193. 
     Accordingly, it is an object of the present invention to provide a novel process for the preparation of bis-(alpha-alkylbenzyl)ethers. 
     Another object of this invention is to provide a process for the preparation of bis-(alpha-alkylbenzyl)ethers from alpha-alkylbenzyl alcohols by employing a mineral acid treated calcined alumina catalyst which provides high selectivity to the desired ether. 
     Yet another object of the present invention involves the preparation of alpha-methylbenzyl ether while employing such treated alumina catalyst from a crude methylbenzyl alcohol-containing stream obtained in olefin oxidestyrene monomer production processes. 
     These and other objects of the present invention will become apparent from the following more detailed description and appended claims. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, bis(alpha-alkylbenzyl)ethers are produced by reacting an alpha-alkylbenzyl alcohol in the presence of a mineral acid treated calcined alumina catalyst of specified characteristics under conditions which form a reaction product containing, in high yield, the desired bis(alpha-alkylbenzyl)ether. A major feature characteristic of the process of the present invention includes the quenching of the catalyst upon completion of the reaction, thereby precluding decomposition of desired bis ether product and high conversions of alcohol reactant over short reaction times while maintaining high selectivity to desired bis ether product. 
     It has now been discovered that the activity of alumina catalysts conventionally employed in dehydration reactions may be substantially increased, thereby rendering such catalysts suitable for use in etherification reactions, by treating a finely-divided calcined alumina with a dilute aqueous solution of a mineral acid and drying the acid-treated alumina. 
     In accordance with one specific embodiment of the invention, commercially available technical grade, alpha-alkylbenzyl alcohols, such as methylbenzyl alcohol, are etherified in the presence of mineral acid treated calcined alumina catalysts to provide, in high yield, commercially acceptable bis(alpha-alkylbenzyl)ethers. 
     In another specific embodiment, methylbenzyl alcohol present in a crude stream obtained from an olefin oxide/styrene monomer process, admixed with acetophenone, 2-phenylethanol, and a variety of other aromatic hydrocarbons and oxygenated derivatives thereof, is contacted with mineral treated catalyst under conditions which provide a high yield of bis(alpha-methylbenzyl)ether. 
     The ethers produced by the process of the present invention find particular use as dielectric fluids for capacitors and carbonless carbon paper solvents. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The process of this invention is applicable to the production of bis(alpha-alkylbenzyl)ethers by etherification of alpha-alkylbenzyl alcohols. In general, the bis(alpha-alkylbenzyl)ethers capable of production in accordance with the process of the present invention correspond to the formula: ##STR1## wherein R is the same or different lower alkyl of 1 to 6 carbon atoms, lower haloalkyl, bromo, chloro, sulfo or nitro; m is an integer not greater than 3 and n is an integer of from 1 to 7, inclusive. The desired ethers of the present invention are obtained by heating an alpha alkylbenzyl alcohol of the formula: ##STR2## wherein R, m and n are as defined above. Exemplary of the alpha alkylbenzyl alcohols which are employed in preparing the desired ethers by the process of the present invention include, but are not limited to: 
     alpha-methylbenzyl alcohol 
     alpha-ethylbenzyl alcohol 
     alpha-(4-chloro-phenyl)-ethanol 
     alpha-(3,4,5-tribromo-phenyl)-ethanol 
     alpha-(4-chloromethyl-phenyl)-ethanol 
     alpha-(4-nitro-phenyl)-ethanol 
     alpha-pentylbenzyl alcohol 
     alpha-(4-bromo-phenyl)-hexanol 
     alpha-(4-sulfo-phenyl)-ethanol 
     alpha-(4-trifluoromethylphenyl)-ethanol 
     alpha-hexylbenzyl alcohol 
     alpha-propylbenzyl alcohol 
     and the like, and mixtures thereof. 
     In producing the bis(alpha-alkylbenzyl)ethers in accordance with the process of the present invention, the alpha-alkylbenzyl alcohol described is heated with agitation at a temperature below about 200° C., generally between about 120° C. and 175° C., and preferably between about 125° C. and 150° C. in the presence of the mineral acid treated calcined alumina catalyst for a time sufficient to effect conversion of at least about 50% of said alcohol to the desired ether, thereby forming a reaction product mixture. 
     The etherification reaction may be carried out in the presence or absence of an inert solvent, such as an aromatic solvent, illustratively, benzene, toluene, acetophenone, or xylene. 
     As is above indicated, it is not necessary that the alpha-alkylbenzyl alcohol employed in the process of the present invention be a pure material. In this connection, an alternative embodiment of the invention resides in the use of an aromatic rich distilland comprising alpha-methylbenzyl alcohol, acetophenone and a variety of other by-products, including alcohols and ketones and other by-products obtained from the olefin oxide-styrene production process. The composition of a typical etherification feed obtained from the propylene oxide/styrene coproduction process is set forth in Table I below: 
     
                       TABLE I______________________________________Component             Weight (%)______________________________________alpha-phenylethanol   75-85acetophenone          10-202-phenylethanol       &lt;5benzyl alcohol        &lt;2benzaldehyde          &lt;1cumylalcohol          &lt;1phenol                &lt;1cumene                &lt;1ethylbenzene          &lt;1______________________________________ 
    
     Water formed during the etherification reaction is removed as formed by distillation, or as an azeotropic mixture with the solvent, if employed, and if desired, its removal may be facilitated in conventional manner by the additional introduction of an inert gas, such as nitrogen, into the reaction system. 
     The catalysts employed in the process of the present invention are preferably in a finely-divided form so that they can be maintained in suspension with minimum agitation. Catalyst concentration in the liquid phase reaction medium may range from about 0.1 to 20.0 weight percent preferably, from about 0.5 to about 15 weight percent. 
     Particularly suitable mineral acids employable in treatment of the calcined alumina are the inorganic oxo acids having the general formula H n  XO m , especially oxo acids wherein m-n&gt;1. See Cotton and Wilkinson, Advanced Inorganic Chemistry, 4th Edition, pp. 235-36, John Wiley and Sons (1980), the disclosure of which is incorporated herein by reference. Preferred acids are sulfuric and orthophosphoric, with sulfuric acid being particularly preferred. 
     The acidic, aqueous treating solution contains from about 0.1 to 10 weight percent of the mineral acid, preferably from about 0.5 to 3 weight percent. At higher acid concentrations, the alumina rapidly deteriorates, even at room temperature. When aqueous solutions of phosphoric acid are used as the treating agent, an aqueous solution containing about 1 percent of the acid is most preferred. When aqueous solutions of sulfuric acid are employed, an aqueous solution containing about 2.5 percent of the acid is most preferred. 
     The alumina content of the slurry formed is generally within the range from about 1-25 weight percent, preferably from about 3 to about 20 weight percent. At the higher concentrations of alumina, less solution needs disposal after treatment, although use of lower alumina concentrations results in slurries which are more readily handled and may produce somewhat more active catalysts. One aspect of the present invention resides in the discovery that the solution separated from the alumina after treatment may be advantageously reused in subsequent alumina treatments. Thus, the disposal problem may be minimized, although higher throughputs may obviously be attained within a given treatment apparatus by operating at the higher ends of the ranges of slurry alumina contents recited above. 
     The acid treatment is effected at temperatures ranging from about 20° C. to 110° C., the upper limit of the temperature range being a function of the desire to maintain a liquid aqueous solution of the mineral acid in the treating zone as well as the desire to minimize destruction of the alumina structure. The residence time of the alumina in the treating zone may range from about 0.1 to about 50 hours, the longer residence times being employed with the lower treatment temperatures. Preferably, the alumina is treated by contacting with the acid solution for a time sufficient to facilitate penetration of the alumina particle core with the aqueous acid solution, generally at a temperature within the range from about 20° C. to 90° C. for 0.2 to 8 hours, and optimally, at a temperature within the range from about 40° C. to 80° C. for 0.2 to 2 hours. Catalyst activities obtained by acid treatment at room temperature are less than those obtained by treatment at elevated temperatures, even with exposure times up to 75 hours. However, at 60° C., the relative activity of the acid treated alumina reaches a maximum very rapidly, the relative activity of the 0.5 hour and 8 hour samples being very similar. 
     After the acid treatment, the treated alumina is generally dried to improve materials handling capabilities, at temperatures ranging from room temperature to about 130° C. for a time sufficient, generally about 15 minutes to about 4 hours, to remove water. Before drying, the alumina may optionally be washed with water to remove residual acid. Although the alumina to be treated according to the process of this invention must be pre-calcined, post-calcination is not necessary to obtain the enhanced characteristics of the catalyst employed in the process of this invention. 
     Although some alumina may be lost as a result of the acid treatment procedure, any amount lost is negligible. For example, alumina losses resulting from treatment with dilute aqueous solutions of phosphoric acid ranges from about 1.5 weight percent to about 3.3 weight percent, the former value being obtained from treatment with 1 percent of H 3  PO 4  at 80° C. for 20 minutes and the latter value being obtained with 1 percent H 3  PO 4  at 100° C. for 60 minutes. Comparable alumina loss data from treatment with sulfuric acid ranged from 1.5 to 2.3 weight percent. These values are quite acceptable when the enhanced catalytic activity of the acid-treated catalyst is taken into account. 
     The alumina treated according to the practice of this invention is an activated alumina having a surface area of at least 15, and preferably of about 40 to 250, square meters per gram as determined by the Brunauer-Emmett-Teller method, and preferably a high-purity gamma alumina such as that sold by Conoco under its &#34;Catapal-SB&#34; trademark. Alumina having low alkali and alkaline earth metal contents as well as low iron contents are desired to minimize by-product formation. Aluminas having combined alkali and alkaline earth metal contents below about 2000 ppm and iron contents below 2000 ppm are preferred. Alumina catalysts are activated by calcining commercially available alumina at a temperature within the range from about 400° to 850° C., preferably 400° to 600° C. for a time from about 0.5 to 24 hours. 
     The mineral acid treating agent may be selected from any of the mineral acids which are known to be effective acid treating agents for alumina, particularly oxo acids, although sulfuric acid is particularly preferred. 
     In accordance with the process of the present invention, the etherification reaction is effected for a time sufficient, generally about 15 minutes to 4 hours, to effect conversion of at least about 50% of the alcohol reactant thereby forming a reaction product mixture. Following completion of the reaction, a basic compound is introduced into the reaction product mixture to deactivate the catalyst, i.e. convert the catalyst to an inert compound. The deactivated catalyst may be removed by conventional separatory procedures, as by filtration, prior to recovery of the desired product. Any basic compound capable of neutralizing acidity of the catalyst may be employed. Illustrative suitable compounds employable for this purpose include alkali and alkaline earth metal hydroxides, carbonates or bicarbonates such as sodium hydroxide, sodium carbonate or sodium bicarbonate. Alternatively, ammonium or ammonium hydroxides or other salts, as well as organic amines such as alkyl amines, illustratively, triethylamine, may be employed for this purpose. It is critical, however, to employ the basic agent in slight excess of the amount sufficient to neutralize (i.e. be just above equivalence in acidity) the catalyst. Neutralization of the catalyst prevents decomposition of the desired ether product. 
     A variety of conventional methods, including distillation, extraction, or physical phase separation may be employed to recover the desired ether reaction product, unreacted starting materials, by-products, impurities, catalysts and diluents, if employed. In general, following removal of the catalyst, lower boiling unreacted starting materials are initially removed in a forecut, by distillation, followed by distillation of the desired ether product, which is carried out generally under vacuum. 
     The process of the present invention may be illustrated by the following examples. All parts and percents are based on weight. The reaction ratio and selectivities are calculated from analysis by Gas Chromotography. 
     This example describes the general experimental procedure used herein to produce bis(alpha-methylbenzyl)ether from pure alpha-methylbenzyl alcohol or a crude mixture, obtained from the propylene oxide/styrene process comprised of 76.23 percent methylbenzyl alcohol 18.72 percent acetophenone, and 5.05 percent of other components described in Table I, above. 
     Into a 250 ml flask equipped with an agitator, a thermometer and a Dean-Stark condenser having a water-measuring tube, there is charged 100 parts of pure or crude alphamethylbenzyl alcohol, as described, in each of a series of experiments. Thereafter, the indicated quantity of catalyst listed in following Table II is added thereto with stirring at the reaction temperature and the mixture is heated at these temperatures for the periods indicated. The catalyst is quenched upon completion of the reaction time indicated with a 29 weight percent aqueous potassium hydroxide solution and is removed by filtration before recovery of the bis(alpha methylbenzyl)ether from the reaction product mixture. Thereafter, the desired bis-alpha methylbenzyl ether is recovered from the reaction mixtures of each Example by distillation at a temperature of 115°-122°/ltorr., following removal of unreacted methylbenzyl alcohol and styrene in a forecut at 75°-110°/ltorr. The results are set forth in Table II, below. 
     
                                           TABLE II__________________________________________________________________________Synthesis of Bis(α-Methylbenzyl) Ether (BAMBE)                                 Selec-                       Conver-   tivity            Temp.                 Reaction                       sion      mol %ExampleFeed   Catalyst °C.                 Time (hr)                       mol %                            Styrene                                 BAMBE                                      Others__________________________________________________________________________1    P.sup.(1)   Amberlyst ® 15.sup.(3)            110-120                 0.5   75.82                            23.08                                 69.24                                      7.682    C.sup.(2)   Amberlyst ® 15.sup.(3)            115-127                 0.5   76.28                            32.56                                 63.44                                      43    P.sup.(1)   Amberlyst ® 15.sup.(3)            115-127                 1     99.52                            25.0 0.8  74.24    P.sup.(1)   Alumina.sup.(4)(7)            130-140                 1     67.03                            8.5  88.34                                      3.25    C.sup.(2)   Alumina.sup.(4)(7)            135-150                 1     66   10.5 86.5 36    C.sup.(2)   Alumina.sup.(5)(7)            135-150                 1     55   15   83   27    C.sup.(2)   Alumina.sup.(6)            135-150                 1     40   27   34   29__________________________________________________________________________ .sup.(1) P = Pure Commercial Methyl Benzyl Alcohol, (98.5 weight percent) .sup.(2) C = Crude Methyl Benzyl Alcohol, comprised of 76.23 weight percent MBA, 18.72 weight percent, Acetophenone, 5.05 weight percent others .sup.(3) A polystyrene based heterogeneous sulfonic acid resin catalyst supplied by Rohm &amp; Haas Company, charged in an amount of 1.0, percent of MBA present .sup.(4) An acid treated catalyst prepared by forming a slurry containing 15 weight percent of finelydivided calcined alumina in a 2.5 weight percent aqueous solution of H.sub.2 SO.sub.4, heating the slurry for 4 hours at 60° C., and drying the acid treated catalyst at 110° C. for 5 hours, charged in an amount of 1.0, percent of MBA present .sup.(5) An acid treated catalyst prepared by forming a slurry containing 4 weight percent of finelydivided calcined alumina in a 2.5 weight percen aqueous solution of H.sub.2 SO.sub.4, heating the slurry for 6 hours at 60° C. and drying the acid treated catalyst at 110° C. for 0.5 hours charged in an amount of 2.0 percent of MBA present .sup.(6) Untreated finelydivided calcined alumina charged in an amount of 2.0 percent of MBA present. .sup.(7) Catalyst quenched with 25 weight percent of KOH, based on the weight of catalyst employed (on a dry basis) 
    
     As is noted from Table II, high purity bis-(alpha methylbenzyl)ether is produced with little decomposition in accordance with Examples 4 5 and 6, illustrative of the process of the present invention; the product ether produced in these Examples was substantially odorless, and of high quality. As is further evident from the results set forth above, use of the Amberlyst catalyst and/or untreated calcined alumina in the process results in a number of drawbacks, including high selectivity to undesired styrene and readily conversion of the ether, once formed, to undesirable by-products.