3,636,177 United States Patent Office Patented Jan. 18, 1972 1. 2 it has been found that the disproportionation and trans 3,636,177 methylation reactions of tetramethylbenzenes proceed in PROCESS FOR PRODUCING DURENE Takashi Suzuki and Hiroyuki Iesaka, Niigata, Japan, quite different manners depending upon the type of assignors to Japan Gas Chemical Company, Inc., diluents used. Thus, in particular it was found that in Chiyoda-ku, Tokyo, Japan 5 producing durene by isomerization of isodurene, prehn No Drawing. Filed May 20, 1970, Ser. No. 39,145 itene, or mixtures of tetramethylbenzenes containing Claims priority, application Japan, May 22, 1969, durene in an amount less than that in the equilibrium com 44/39,121 position, it is possible to produce durene without decreas int, C. C07c5/28 ing the rate of isomerization, while effectively suppressing U.S. C. 260-668 A 7 Claims O the disproportionation or transmethylation reaction of tetramethylbenzenes by carrying out the isomerization in the presence of benzene or polymethylbenzenes having 9 ABSTRACT OF THE DISCLOSURE or less carbon atoms. Durene is produced in high yield by isomerizing other According to the present invention, durene is produced tetramethylbenzenes with a HF-BF catalyst in the by isomerization of isodurene, prehnitene, or mixtures of liquid phase in the presence of a diluent comprising ben tetramethylbenzenes in liquid phase in the presence of zene or methyl-substituted benzenes having 9 or less HF-BF3 catalyst. The isomerization is carried out in carbon atoms, whereby suppressing disproportionation and the presence of benzene or methyl-substituted benzenes transmethylation of tetramethylbenzenes. containing 9 or less carbon atoms to suppress the normal 20 ly concurrent disproportionation and transmethylation -nous summon reaction of tetramethylbenzenes. This invention relates to a process for producing The starting material used in the present process may durene by isomerization of isodurene, prehnitene, or mix be isodurene, prehnitene, or mixtures of tetramethylben tures of tetramethylbenzenes. Zenes containing durene in an amount less than that in Durene is an important substance as the basic starting 25 the equilibrium composition. Therefore, the feed material material for the production of synthetic resins and fibers, may be a mother liquor obtained by cooling a mixture and is obtainable by various manufacturing methods. of tetramethylbenzenes containing an almost equilibrium However, in every known method mixtures of tetramethyl amount of durene and separating the crystallized durene benzene isomers are formed so that it is not easy to obtain from said mixture, or it may be a concentrated isodurene essentially pure durene, and also the yield of durene is 30 obtained by extraction with HF-BF as an extractant. greatly reduced due to the formation of the tetramethyl The feedstock can also comprise a mixture of tetra benzene isomers. Therefore, it has been necessary to isom methylbenzenes having not only the aromatic hydrocarbon erize the by-product tetramethylbenzene isomers other fraction having 10 carbon atoms, which is obtained from than durene into durene, and separate the durene selec the catalytic reformate or thermal cracking residue of tively from the reaction mixture thus obtained. 35 petroleum fractions, but also the reaction products ob It is known in the art to isomerize polymethylbenzenes tained by disproportionation reaction or methylation of with an acidic catalyst in the liquid or gaseous phase; how trimethylbenzenes and other reaction products containing ever, disproportionation and transmethylation reactions, tetramethylbenzenes. which give rise to other difficult problems during the As the diluent in the present process, there may be process, occurs concurrently with the isomerization. The 40 used benzene, toluene, o-Xylene, p-Xylene, m-xylene, disproportionation and transmethylation reactions result hemimellitene, pseudocumene and mesitylene, each alone in an undesirable conversion of tetramethylbenzenes to or in combination. When the raw material already con pentamethylbenzenes and hexamethylbenzenes instead of tains the present diluent, as in the case when the mixture durene. This, in turn results in an additional load on the containing tetramethylbenzenes obtained by dispropor separation and purification procedures for obtaining the tionation reaction or methylation as mentioned above, durene produced. it can be used directly as the starting material. The diluent The liquid phase process for isomerizing polymethyl hydrocarbon is used in a proportion of 20 to 200 parts benzenes using a catalyst consisting of hydrogen fluoride (the term "part” used herein means part by mole), pref and boron trifluoride has an advantage in that the catalyst erably 50 to 150 parts per 100 parts of tetramethylben has low temperature activity whereas the solid catalyst 50 Zenes. The use of more than 200 parts of the diluent is of employed in the gaseous phase process does not. U.S. Pat. no advantage. Since the amount of boron trifluoride to be No. 2,784,242 proposed a method for preparation of used as catalyst affects the isomerization rate and dispro durene by isomerizing polymethylbenzenes in the presence portionation rate, as well as the equilibrium composition of a HF-BF3 catalyst. However, this process has no of the tetramethylbenzenes, it must be predetermined ac practical use due to the concurrence of the dispropor 55 curately. The amount of boron trifluoride generally used tionation of polymethylbenzenes. is within the range of 1 to 20 parts, preferably 4 to 13 The use of saturated hydrocarbons, which are inert parts. The use of more than 20 parts of boron trifluoride under a HF-BF atmosphere, has been proposed to sup is undesirable because of its promoting effect on side re press the disproportionation and transmethylation re actions and its deteriorating effect of decreasing the con actions by their dilution effect. However, unlike the case 60 tent of durene in the equilibrium composition. The use in the production of xylenes where a saturated hydro of less than 1 part of boron trifluoride is unpractical be carbon such as n-heptane suppresses the disproportiona cause the isomerization rate becomes so slow that an ex tion reaction, in the case of tetramethylbenzenes, con cessively long time will be necessary before the equi trary to the case the disproportionation or transmethyla librium state is attained. 65 The amount of hydrogen fluoride to be used is gen tion reaction cannot be suppressed by the use of saturated erally within the range of 30 to 300 parts, preferably 50 hydrocarbons as a diluent in the production of durene. to 250 parts. The most suitable amount is determined The object of this invention is to provide a process for relative to the amount of boron trifluoride, because the producing durene by isomerization of tetramethylbenzenes amount of hydrogen fluoride should be within the range while suppressing the occurrence of Side reactions. 70 where the co-existing boron trifluoride will act most ef From the present study on the isomerization reaction of fectively as catalyst, said range being 0.04 to 0.20 mole, tetramethylbenzenes in the presence of HF-BFs catalyst, preferably 0.08 to 0.15 mole of boron trifluoride per mole 3,636,177 3. 4 of hydrogen fluoride. When mole ratios outside of said and analyzed by gas chromatography. The results were as range are used disadvantages such as promotion of the dis shown in Table 1. proportionation or transmethylation reaction of tetrameth ylbenzenes, and suppression of the isomerization rate may EXAMPLES 2-4 be brought about. Under the conditions set forth above, the isomeriza Reactions were carried out in the manner similar to that tion reaction in the present process may reach an equilib in Example 1. The reaction conditions and the analytical rium state in about 30 minutes at a temperature of 80 to results were as shown in Table 1. 120° C., preferably 90 to 110° C. At temperatures below 80° C. the isomerization reaction proceeds without any O inconvenience but somewhat slower and the completion TABLE of reaction is prolonged. At temperatures above 120° C., the increase in the rate of isomerization is accompanied Example------------------------------- i 2 3. 4. by promotion of the disproportionation reaction. As for Feed (moles): Tetramethylbenzene.---------------- 1.00 the pressure, there is no particular limitation. The isom Benzene---------------- 1.00 erization is usually carried out under the autogenous vapor Hydrogen fluoride------ 1.00 O 5 0. Boron trifluoride------------------- 0, 10 pressure at the reaction temperature, which generally Reaction conditions: . ranges from 2 to 20 kg./cm.?. Reaction period (min.)------------- 30 Temperature (C.)----------- - - - - - - 00 8 The equilibrium mixture of tetramethylbenzenes ob Composition of hydrocarbons in re tained in the present process is composed of approximate action product (percent by mole): Benzene. 50. 50. ly 45 percent of durene, 50 percent of isodurene and 5 Toluene. percent of prehnitene, and is distributed between two Xylene Trimethylbenzene.-- immiscible layers, a catalyst phase (HF phase) and a Tetramethylbenzene.--------------- as: hydrocarbon phase. The basicity of tetramethylbenzene Pentamethylbenzene.--------------- Composition of tetramethylbenzene i isomers with respect to hydrogen fluoride and boron tri 25 (percent by mole): fluoride differs widely from each other. Isodurene pre Dureme-----------------------------