Disproportionation alkylbenzene

The participation of protonic acid sites in xylene isomerization is clearly demonstrated by correlations between the isomerization rate and the concentration of protonic sites of silica alumina with various alumina contents (13), alkaline-earth and rare earth FAU zeolites (14, 15), MFI zeolites (16), etc. Evidence is also provided by the fact that protonic sites participate in alkylbenzene disproportionation. On the other hand, it seems most unlikely that Lewis acid sites play a direct role in xylene isomerization and disproportionation (8). 

Deall lation, Transall lation, and Disproportionation. The action of aluminum chloride also removes alkyl groups from alkylbenzenes (dealkylation, disproportionation) (12). Alkylbenzenes, when heated with AlCl, form mixtures of benzene and polyalkylated benzenes ... 

Tsai, T.-C., liu, S.-B., and Wnag, I. (1999) Disproportionation and trans-alkylation of alkylbenzenes over zeolite catalysts. Appl Catal A, 181, 355-398. 

Superacids were shown to have the ability to effect the protolytic ionization of a bonds to form carbocations even in the presence of benzene.190 The formed car-bocations then alkylate benzene to form alkylbenzenes. The alkylation reaction of benzene with Ci—C5 alkanes (methane, ethane, propane, butane, isobutane, isopentane) are accompanied by the usual acid-catalyzed side reactions (isomerization, disproportionation). Oxidative removal of hydrogen by SbF5 is the driving force of the reaction ... 

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... 

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... 

It was shown that the SbF5-intercalated graphite efficiently promotes disproportionation of various alkylbenzenes by simple mixing at room temperature (41). The isomerization of methylpentanes was carried out over the catalyst at room temperature, -30, and - I7°C in a continuous flow system a careful study of the kinetically controlled product distribution was performed to obtain information for the reaction path (42, 43). The skeletal rearrangements of l3C- abeled 2-methyl, 3-methylpentane and... 

Toluene, an alkylbenzene, has the chemistry typical of each example of this type of compound. However, the typical aromatic ring or alkene reactions are affected by the presence of the other group as a substituent. Except for hydrogenation and oxidation, the most important reactions involve either electrophilic substitution in the aromatic ring or free-radical substitution on the methyl group. Addition reactions to the double bonds of the ring and disproportionation of two toluene molecules to yield one molecule of benzene and one molecule of xylene also occur. 

H.G.Karge,K.Hatada,Y.Zbang.R.FIedoraw Conversion of Alkylbenzenes over Zeotfle Catalysts 1l Dealky1ation and Disproportionation of Ethylbenzene over Faujasite-Type 2bol ites. Zeolites (19 )... 

From their studies on dealkylation of alkylbenzenes with AICI3 at 100 C, Roberts et al. found that, in general, the catalyst and experimental conditions required to produce dealkylation are forceful enough to effect several other reactions, such as disproportionation, isomerization, rearrangement of the side chain and fragmentation. The latter refers to a process in which the alkylbenzene affords alkanes and alkylbenzenes with fewer carbons than those in the original alkyl side chain. Formation of alkanes in the dealkylation process can take place even in the absence of an added hydride donor agent. In this case, a second molecule of the alkylbenzene acts as the hydride donor. 

The least satisfactory method involves the addition of an acyl halide to a mixture of the aluminum halide and the aromatic compound (the Bouveault procedure). The problem with this sequence relates to the presence of hydrogen halide, which may be present as a result of the reaction of moisture with the aluminum halide or which will be present in increasing amounts as the reaction proceeds. The hydrogen halide can result in isomerization or disproportionation of, for example, alkylbenzenes. 

Conversion of alkylbenzenes over zeolite catalysts. I-Dealkylation and disproportionation of ethylbenzene over... 

In the absence of antifoam, the foam volume of each of these solutions of alkylbenzene sulfonate was stable for up to 1800 s after foam generation ceased (although bubble disproportionation and drainage significantly affected the appearance of the foam). A measure of the effectiveness of the antifoam after foam generation has ceased is the ratio F(t = 960 s)/F(t = 0), where t is the foam age and where we remember F = volume of air in foam in the presence of antifoam/volume of air in foam in the absence of antifoam. In effect, the ratio F(t = 960 s)/F(f = 0) is the ratio of the volume of air in the foam in the presence of antifoam after 960 s to the volume of air in the foam in the presence of antifoam immediately after foam generation has ceased. This follows because the foam volume is stable in the absence of antifoam. The ratio F(t = 960 )/F t = 0) has the value of unity if Fdoes not change with the age... 

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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