Alkylbenzenes transalkylation

Disproportionation (transalkylation) and positional isomerization usually take place simultaneously when either linear or branched alkylbenzenes are treated with conventional Friedel-Crafts catalysts or with Nafion-H. The reactivity of alkyl groups to participate in transalkylation increases in the order ethyl, propyl < isopropyl < tert-butyl.117 207 217... 

The transalkylation of fm-alkylbenzenes follows a different route, since they have no abstractable benzylic hydrogen. They were shown to transalkylate by a dealkylation-transalkylation mechanism with the involvement of free ferf-alkyl cations. The exceptional ability of fcrt-alkyl groups to undergo transalkylation led to the extensive utilization of these groups, especially the fm-butyl group, as positional protective groups in organic synthesis pioneered by Tashiro.223... 

Transalkylation. Advances in research and developments with respect to disproportionation and transalkylation of alkylbenzenes, particularly the transformation of toluene to produce xylenes, are adequately treated in reviews.446-449 A review is available for de-fm-buty 1 ation 450... 

The acidity of perfluorinated sulfonic acids can be increased further by complexa-tion with Lewis acid fluorides, such as SbF5, TaF5, and NbF5.183 They have been found to be effective catalysts for n-hexane, n-heptane isomerization, alkylation of benzene, and transalkylation of alkylbenzenes (see Chapter 5). 

Effluents from the alkylation and transalkylation reactors are fed to the benzene column (3), where unreacted benzene is recovered from crude EB. The fresh benzene feedstock and a small vent stream from the benzene column are fed to the lights column (4) to reject light impurities. The lights column bottoms is returned to the benzene column. The bottoms from the benzene column is fed to the EB column (5) to recover EB product. The bottoms from the EB column is fed to the PEB column (6) where recyclable alkylbenzenes are recovered as a distillate and diphenyl compounds are rejected in a bottoms stream that can be used as fuel. 

Transalkylation of alkylbenzenes, polyalkylbenzenes and other arenes can be brought about by a variety of catalysts including Lewis acids, Brpnsted acids and various zeolites and silicates with or without being doped with various transition metals or their oxides. There has been a particularly explosive growth in the volume of literature pertaining to the use of various natural and modified zeolites. Recent developments include the study and applications of shape-selective catalysis by zeolites. Much of the work is patented, and largely applies to industrial processes. 

To a very small extent EB undergoes alkylation to diphenylethane. The DEB and TEB can be easily recovered by transalkylation with benzene to EB, so they can be considered useful products. Conversely, the formation of olefins and other alkylbenzenes heavily affects the efficiency of the process by increasing the specific consumption of ethylene and benzene and reducing the EB quality. 

Benzene and toluene afford benzaldehyde and p-tolualdehyde in 90% and 85% yield respectively using the atmospheric pressure methods, and biphenyl has been converted into 4-formylbiphenyl in yields as high as 73%. With some alkylbenzenes there is, however, a tendency for dealkylation or transalkylation reactions to occur during the course of the reactions. Thus p-xylene gives 2,4-dimethylbenzal-dehyde and triisopropylbenzene gives only diisopropylbenzaldehydes. Naphthalene appears not to give a naphthaldehyde. 

Transalkylation of biphenyl with alkylbenzene is another way to obtain 4,4-dialky Ibiphenyl. Recently, Takeuchi and coworkers reported on transalkylation of biphenyl with triethylbenzene over Y-zeolite [Takeuchi et al., 1996]. A comprehensive review of literature on... 

Other reactions that occur over the Cyclar catalyst are isomerization, dealkylation, and transalkylation of the aromatics species formed in the main reaction mechanism. The transalkylation reactions result in a distribution of benzene and alkylbenzenes that depends on the charge stock and process conditions. Slightly more benzene is produced from propane than from butane-rich feedstocks. ... 

Lewis acids supported on graphite as well as the perfluorinated resin sulfonic acids (Nafion-H) have been studied for their abilities to perform Friedel-Crafts alkylation of benzene and transalkylation of alkylbenzenes (Olah et aL, 1977). The graphite-supported materials were less stable than the perfluorinated resin sulfonic acid. Subsequent studies investigated the use of this latter resin in the methylation of phenols, benzene, and alkylbenzenes (Kaspi and Olah, 1978 Kaspi et aL, 1978), the nitration of aromatics (Olah et aL, 1978a), the rearrangement of allyl alcohols to aldehydes (Olah et al., 1978b), the pinacolone rearrangement (Olah and Meidar, 1978) and isomerizations of alkylbenzenes (Olah and Kaspi, 1978). 

Formation of ethylene via alkyl cyclopentyl carbenium ion. Adapted from Tsai T-C, LiuS-B, Wangl. Disproportionation and transalkylation of alkylbenzenes over zeolite catalysts. AppI Catal A 1999 181 355-98. 

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