ACID-CATALYZED ISOMERIZATION OF DIALKYLBENZENES

Isomerization and transalkylation are the principal reactions of 1-methyl-2-ethylbenzene over silica-alumina cracking catalyst and partially multivalent cation-exchanged, partially decationized Y-type faujasite molecular sieves. Isomerization proceeds by two different mechanisms. The first type consists of intramolecular 1,2 shifts. Trans alkylated intermediates are involved in the second reaction. Xylenes and diethylbenzenes may be formed from methylethylbenzene by the same type of transalkylated intermediates. We suggest the name “alkyl exchange” for this reaction. The extent of intermolecular isomerization may be estimated from the level of alkyl exchange. The contribution of intermolecular isomerization decreases with increasing temperature. Above 300° isomerization primarily occurs by intramolecular 1,2 shifts. Below 200° isomerization via transalkylated intermediates predominates. At intermediate temperatures intermolecular and intramolecular processes contribute to over-all isomerization to a similar extent. © 1969, American Chemical Society. All rights reserved.