3,187,057 United States Patent Office Patented use 1, 1965 1. 2 3,187,057 substituents attached to the benzene ring may be ethyl TRECHL{ROMETHYL POLYMETHYL SENZENES groupings. The alkyl substituent may be an n-propyl-, Hugo H. Peter, The Hague, Netherlands, and Meivern C. isobutyl-, or tertiary butyl substituent, but with these Hoff, Highland, Ind., assignors to Standard Oil Com larger alkyl substituents only one such substituent may be pany, Chicago, Ill., a corporation of adiana present in the polyalkylbenzene in order to be useable in No Drawing. Filed May 19, 1958, Ser. No. 735,961 the process of this invention. To illustrate, 1,3-dimethyl 10 Claims. (CI. 260-651) 5-tertiary butyl benzene may be used in the reaction, but 1,3,5-tri tertiary butylbenzene is not useable in the proc This invention relates to reactions between polyalkyl ess. It is important that polyalkylbenzenes which contain benzenes and carbon tetrachloride and particularly con O their alkyl substituents in the 1,3,5-, 1,2,4,5-, 1,2,3,5-, or cerns a method for forming trichloromethyl polyalkyl in the 1,2,3,4,5-positions in the benzene nucleus be used. benzenes. The benzylic chlorines on the intermediate trichloro Prior workers have attempted to prepare trichloro methyl aromatic are far more reactive than the compet methylbenzene by reacting benzene with carbon tetrachlo ing halogens on the carbon tetrachloride. The polyalkyl ride in the presence of aluminum chloride. The reaction 5 benzenes which are substituted in the above defined posi did not stop at the desired stage, but instead continued tions provide steric protection and shelter the reactive and produced dichlorodiarylmethane and chlorotriary trichloromethyl grouping in such fashion as to prevent methane. The uncontrollable nature of the reaction was reaction with second or even third molecules of the aro also heretofore observed when toluene was used in the re matic. To illustrate, when mesitylene is used under the action rather than benzene. On hydrolyzing the reaction 20 preferred processing conditions an essentially quantitative products diaryl ketones and triaryl carbinols are formed. yield of the trichloromethyl mesitylene can be produced. Recent interest in polyalkylbenzoic acid for use in plasti However, if benzene is used most of the product consists cizers, paints, varnishes, etc. poses a problem as to how to of dichlorodiphenylmethane and chlorotriphenylmethane. prepare such carboxylic acids. In carrying out the reaction, it is preferred to add the An object of the present invention is to provide a proc 2 5 polymethylbenzene to a mixture of the aluminum chloride ess for producing trichloromethyl polymethylbenzenes. and carbon tetrachloride. This sequence of addition of Another object is to provide a process which produces tri the reactants minimizes the amount of isomerization and chloromethyl polymethylbenzenes in good yields and at disproportionation of the polymethylbenzene. It is par the same time minimizes or avoids the production of di ticularly important to do so when using durene since the chlorodiarylmethanes, chlorotriarylmethanes, tars and latter readily isomerizes to isodurene. The polymethyl other undesired byproducts. A still further object is to benzene may be added gradually to the aluminum chlo provide a process for producing trichloromethyl poly ride-carbon tetrachloride slurry, for example over a course methylbenzenes which are hydrolyzable to polymethyl of 0.1 to 2 hours. The reactants are usually maintained benzoic acids and minimizing the formation of products at a temperature of from -20 to 100° C. Somewhat which are hydrolyzable to ketones. Other objects and higher or lower temperatures may be used, however, with advantages of the present invention will be apparent from out adverse results. Reaction times of about 1 to 2 hours the more detailed description thereof. are usually satisfactory although the reaction may be car In accordance with the present invention, a polyalkyl ried out over a shorter period of time, e.g. 0.1 hour or benzene such as polymethylbenzenes selected from the for as iong as 10 hours or more. To avoid the formation group consisting of mesitylene, durene, isodurene and pen of condensation products, dichlorodiarylmethanes, and tamethylbenzene are agitated with carbon tetrachloride chlorotriarylmethanes, carbon tetrachloride should be and aluminum chloride, the amount of carbon tetrachlo used in the reaction Zone in an amount in excess of one ride being in excess of one mol per mol of polyalkylben mol of the latter per mol of introduced polymethylben Zene. It is preferred to carry out the reaction by gradually Zene, e.g. a molar ratio of 2:1 to 10:1 is usually satisfac adding the polyalkylbenzene to a mixture of aluminum 45 tory. For this same purpose, and to avoid the formation chloride and carbon tetrachloride. To avoid the forma of tar as the product, a molar ratio of aluminum chloride tion of tarry products it is desirable to employ more than to polymethylbenzene of at least 2:1, e.g. 2:1 to 10:1, two mols of aluminum chloride per mol of polyalkyl should be employed in the reaction zone. A high ratio of benzene. Reaction temperatures of from 0 to 100° C. aluminum chloride to polymethylbenzene is maintained may be used. After the polyalkylbenzene charge stock is in the reaction zone also by the mode of addition of react converted to the trichloromethyl polyalkylbenzene, the ants which is used, i.e. by adding the polymethylbenzene latter can be recovered from the reaction products, or the gradually to a slurry of aluminum chloride and carbon reaction products may be hydrolyzed to form the poly tetrachloride. Maintaining a high molar excess of alu alkylbenzoic acid from the trichloromethyl polyalkyl minum chloride to polymethylbenzene in the reaction zone benzene. is important in reducing and preventing the formation of Using mesitylene as an example polymethylbenzene, the tarry products. chemical reaction involved in the present invention ap During the course of adding the reactants, the slurry pears to be as follows: of polymethylbenzene with carbon tetrachloride and alu minum chloride is agitated. Some heat is given off dur (H, CEI 60 ing the reaction. Agitation is preferably continued dur ing the course of the reaction. Thereafter the reaction - C Cl4 -} CCl3 Hol products may be worked up to recover the trichloromethyl polymethylbenzene. Since a principal utility for these CH3- - C3 CH- -CH3 trichloromethyl polymethylbenzenes is in the formation of 65 polyalkylbenzoic acids, the latter may be formed directly While the invention is being described herein as using from the reaction products of this invention by adding polymethylbenzenes selected from the group consisting of aqueous caustic solution or other hydrolyzing media to mesitylene, durene, isodurene, pentamethylbenzene, and the reaction products. The trichloromethyl polymethyl mixtures of such polymethylbenzenes, it is apparent that benzenes are hydrolyzed to their corresponding polyalkyl other polyalkylbenzenes whose substituents are attached 70 benzoic acids. These are thereafter recovered by conven in the 1,3,5- or in the 1,2,4,5- or in the 1,2,3,5-, or in the tional techniques such as distillation, crystallization or 1,2,3,4,5-position may be used. For instance, all of the other suitable methods. s 3,187,057 3 If a mixture of trichloromethyl polymethylbenzenes is mols) of carbon tetrachloride was then added at a very desired, the charge polymethylbenzene may be subjected slow rate. The reaction was carried out and the products to a preceding isomerization step using an aluminum chlo were worked up as described in Example 1. The result ride catalyst, and carbon tetrachloride may then be added ing crude mesitoic acid weighed 84 grams (102% of to the reaction zone whereupon the isomerized and/or theory) and melted at 142-145 C. Two recrystalliza disproportionated polymethylbenzene is converted to its tions from n-heptane yielded 69 grams (84% of theory) corresponding trichloromethyl polymethylbenzene. For of mesitoic acid having a melting point of 155° C. (155 example, one mol of pseudocumene may be agitated with C. Beilstein X, 553). one to two mols of aluminum chloride and one mol of Example 3 hydrogen chloride at about 80° C. for one hour, the tem 10 perature lowered to 20 C. and agitated for two more The experimental techniques described in the preceding hours. The product polymethylbenzenes at this stage will examples were followed in a run in which a mixture of consist of 60% trimethylbenzenes of which 95% is polymethylbenzenes consisting of 82% isodurene, 8% mesitylene, 20% tetramethylbenzenes of which the main prehnitene and 10% durene was used. The tetramethyl portion is isodurene, and the remainder is principally 5 benzene mixture together with carbon tetrachloride was xylenes. Carbon tetrachloride is then added in a molar slowly added to the slurry of aluminum chloride and excess based upon polymethylenzene and the reactants are carbon tetrachloride. The molar ratio of aluminum chlo agitated at about 30° C. for two hours following which ride to the total tetramethylbenzene added was 2.14:1. The the trichloromethyl derivatives of the tri- and tetrameth reaction temperature was maintained at about 30° C. ylbenzenes may be recovered or hydrolyzed to their cor 20 From the hydrolyzed reaction products was obtained a responding benzoic acids and then recovered. The in- . 53% of theory yield of mixed acids having a melting point dividual polymethylbenzoic acids may then be separated of 123-127 C. In a companion experiment in which all from each other. Mixtures of trimethylbenzene can thus conditions were held the same except that the molar be isomerized to an equilibrium composition which is 90 ratio of aluminum chloride to the total amount of added to 95% mesitylene which may thereafter be processed in 25 tetramethylbenzene was 1.14:1, substantially all of the accordance with this invention.