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 proceed in PROCESS FOR PRODUCING 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 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, , 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 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 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, , o-, p-Xylene, m-xylene, disproportionation and transmethylation reactions result hemimellitene, pseudocumene and , 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 , 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 where a saturated hydro of less than 1 part of boron trifluoride is unpractical be carbon such as n- 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 50. 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------Isodurene.---- W - - 5 dominately forms a complex with HF-BF and is selec Prehnitene.------tively dissolved in the catalyst phase. Hence, the propor Degree of disproportionation of tetra t tion of isodurene to other isomers becomes far greater in methylbenzene (percent).------t i the catalyst phase than in the hydrocarbon phase, and ac cordingly the proportion of durene and prehnitene is smaller in the catalyst phase. Consequently, the isom erization of tetramethylbenzenes may be conducted in a COMPARATIVE EXAMPLES 1-2 continuous manner by separating the catalyst phase from the hydrocarbon phase by phase separation without de Reactions were carried out in the manner similar to that composing the complex with HF-BF, and recycling the in Example 1 except that no diluent was used. The reac catalyst phase as the feed material to the reactor. tion conditions and the analytical results were as shown The product durene is recovered in the form of crystals in Table 2. by cooling the hydrocarbon phase at 0° C., or by distillat COMPARATIVE EXAMPLE 3 ing off from the raffinate containing durene and prehnitene, 40 The reaction was carried out in the manner similar to obtained by extracting isodurene completely into the cata that in Example 1 except that commercial grade n- lyst phase after the addition of further amount of containing methylcyclopentane and isohexane in addition HF-BF3. By either one of said procedures durene in a purity of more than 95% may easily be obtained. to n-hexane was used as the diluent. The reaction condi The process of the present invention will be illustrated tions and the analytical results were as shown in Table 2. by the following examples. The tetramethylbenzene mix ture used in the examples was composed of 10.4 percent TABLE 2 by mole of durene, 88.8 percent by mole of isodurene, and 0.8 percent by mole of prehnitene, the purity as tet Comparative Example------2 3 ramethylbenzenes being more than 98 percent. The de Feed (mole): gree of disproportionation of tetramethylbenzene was cal Tetranethylbenzene. 00 1,00 1.00 Diluent------1.00 culated from the equation, Hydrogen fluoride- 100 0.50 1.00 Borontrifluoride--- 0.18 0.07 0.15 Reaction conditions: Reaction period (min.)------30 30 30 Temperature (C.)------00 00 0 5 5 Composition of hydrocarbons in reaction Degreeof tetramethylbenzene of distrationation) product (percent by mole): Benzene-- 0. 0. O Moles of Cio-hydrocarbons in Toluene. 0. O 0 Xylene--- 0.4 0.6 0.3 = 100 reaction mixture )x100 Trimethylbenzen 4.4 9.3 7.5 Moles of Co- and 2C1-hydro Tetramethylbenzene- 69.5 82.5 34.9 carbons in reaction mistar) 60 Pentanethylbenzene.-- --- i5.7 7.6 7.3 Compositionn-Hexane------of tetramethylbenzene (percent 50.0 by mode): EXAMPLE 1. Durene------43.6 33.7 4.4 Isodurene... 51.9 61.6 48.0 1.00 mole of tetramethylbenzene and 1.00 mole of ben DegreePrehnitene------of disproportionation of tetramethy 4.5 4, 4, 6 Zene were charged into a 400 cc. autoclave provided benzene (percent)------3.1 15.5 29.5 with an electromagnetic stirrer, and the autoclave was cooled to 15° C. After the addition of 1.00 mole of an 1 n-Hexane. hydrous hydrogen fluoride, the autoclave was heated to 100 C. while being stirred vigorously. 0.10 mole of boron trifluoride was introduced from a measuring tank into the EXAMPLES 5-7 autoclave while maintaining the temperature at 100° C., whereby the pressure in the autoclave rose to 6.0 kg/cm.2 Reactions were carried out in the manner similar to that (gauge). The stirring was stopped after 30 minutes and in Example 1 except that toluene, xylene, or trimethyl the contents of autoclave were drawn off. The reaction benzene was used as the diluent. The reaction conditions product was washed with water to remove the acid, dried 5 and analytical results were as shown in Table 3. 3,636,177 5 6 TABLE 3 substituted benzenes having 9 or less carbon atoms and mixtures thereof. Example------5 6 7 2. A process for producing durene by isomerizing under Feed (mole): Tetramethylbenzene------1.00 0.60 0.60 heating isodurene, prehnitene or a mixture of tetra methyl Diluent------1 1.00 20.60 30.60 benzenes in liquid phase in the presence of a catalyst FIydrogen fluoride-- 1.00 0, 60 0.60 Borontrifluoride------0.10 0.08 0.07 consisting of hydrogen fluoride and boron trifluoride, Reaction conditions: which comprises conducting said isomerization reaction Reaction period (min.)---- 30 30 30 Temperature (C.).------100 00 100 in the presence of a diluent chosen from benzene, methyl Composition of hydrocarbons in reaction product (percent by mole): substituted benzenes having 9 or less carbon atoms and Benzene------mixtures thereof at a temperature of 80 to 120° C., said Toluene. 5 Xylene------catalyst being used in said isomerization reaction in the Trimethylbenzene-- amount of 1 to 20 moles of boron trifluoride and 30 to Tetramethylbenzen PentaImethylbenzene 300 moles of hydrogen fluoride each per 100 moles of Composition of tetramethylbenzene (percent s i i the tetramethylbenzenes, provided that the mole ratio of by mole): boron trifluoride to hydrogen fluoride is 0.04 to 0.20 in Durene------said catalyst. Isodurene--- 3. A process according to claim 1 or 2, wherein the Degree of disproportionation of tetramethy methyl-substituted benzene is toluene, o-xylene, p-xylene, benzene------0 8 0. S 3 m-xylene, hemimellitene, pseudocumene, mesitylene or a 1 Toluene. 2p-Xylene. mixture thereof. 3 Pseudocumene. 4. A process according to claim 1 or 2, wherein the diluent is used in an amount of 20 to 200 moles per 100 EXAMPLE 8 moles of the tetramethylbenzenes. 1.00 mole of 1,2,4-trimethylbenzene was charged into 5. A process according to claim 1 or 2, wherein the an autoclave similar to that used in Example 1. After the 2 5 mixture of tetramethylbenzenes is a fraction of aromatic addition of 5.0 moles of hydrogen fluoride and 0.5 mole hydrocarbons having 10 carbon atoms obtained from the of boron trifluoride, the autoclave was heated to and at catalytic reforming or thermal cracking of petroleum. 100° C. with stirring to allow the disporportionation reac 6. A process for producing durene by isomerizing under tion to proceed for one hour. After the reaction was com heating tetramethylbenzenes in the presence of a catalyst plete, the reaction product was poured into ice water, and 30 consisting of hydrogen fluoride and boron trifluoride, washed with water to remove the acid. After being dried, which comprises conducting said isomerization reaction the reaction product was analyzed by gas chromatography. by heating a reaction mixture resulted from the dispro The results obtained were as shown in column A of Table portionation reaction or methylation of trimethyl ben 4. The degree of disproportionation was found to be Zenes at a temperature of 80 to 120° C., said catalyst 41.5%. being used in said isomerization in the amounts of 1. After the addition of 1 mole of hydrogen fluoride and to 20 moles of boron trifluoride and 30 to 300 moles of 0.1 mole of boron trifluoride to said disproportionation hydrogen fluoride each per 100 moles of the tetramethyl product containing xylenes and trimethylbenzene, the isom benzenes, provided that the mole ratio of boron trifluoride erization reaction was allowed to proceed under the same to hydrogen fluoride is 0.04 to 0.20 in said catalyst. conditions and in the same way as those in Example 1. 40 7. A process for producing durene by isomerizing under The results obtained were as shown in column B of Table 4. heating isodurene, prehnitene or a mixture of tetramethyl benzenes in liquid phase in the presence of a catalyst TABLE 4. consisting of hydrogen fluoride and boron trifluoride, Composition of hydrocarbons which comprises conducting said isomerization reaction (percent by mole) A. in the presence of a diluent chosen from benzene, methyl Benzene------Substituted benzenes having 9 or less carbon atoms and Toluene--- a mixture thereof at a temperature of 80 to 120° C., said Xylenes.------p-Xylene.-- catalyst being used in said isomerization in the amounts o-Xylene.-- m-Xylene---- of 1 to 20 moles of boron trifluoride and 30 to 300 moles Trimethylbenzen of hydrogen fluoride each per 100 moles of the tetrameth 1,3,5------ylbenzenes, provided that the mole ratio of boron tri 1,2,4----- i fluoride to hydrogen fluoride is 0.04 to 0.20 in said catalyst, 2 l,2,4,5--- separating the resultant reaction mixture into a catalyst 1,2,3,5- layer and hydrocarbon layer, recycling the catalyst layer 1,2,3,4- 55 containing isodurene to the isomerization reaction system, Polymethylbenzene '. and recovering durene from the hydrocarbon layer. What is claimed is: References Cited 1. A process for producing durene by isomerizing under UNITED STATES PATENTS heating isodurene, prehnitene, or a mixture of tetrameth 60 ylbenzenes in liquid phase in the presence of a catalyst 2,784,242 3/1957 Lien et al. ------260-668A consisting of hydrogen fluoride and boron trifluoride, 2,814,651 11/1957 McCaulay ------260-668A which comprises conducting said isomerization reaction 3,219,720 11/1965 Binder et al. ----- 260-668A in the presence of a diluent chosen from benzene, methyl C. R. DAVIS, Primary Examiner