Dealkylation of alkyl-substituted aromatic hydrocarbons in presence of an aluminum silicate catalyst Communication 2. Kinetics of the dealkylation of dialkylbenzenes

Abstract

1. The main reaction in the cracking of the three isomeric cymenes and p-diisopropylbenzene is the elimination of the isopropyl group from the benzene nucleus with formation of toluene in the cracking of cymenes and of benzene and cumene in the cracking of p-diisopropylbenzene. In the dealkylation of p-diisopropylbenzene successive reactions probably occur, with formation of an intermediate compound, cumene, which is then dealkylated to benzene. Reactions of redistribution of hydrogen, isomerization, and polymerization occur only to a slight extent and affect only the products from the decomposition of the eliminated isopropyl group. 2. The apparent activation energies are 12,000 cal/mole for o-cymene, 14,000 cal/mole for m-cymene, and 13,000 cal/mole for p-cymene. 3. When a hydrogen atom of the cumene molecule is replaced by a methyl group the activation energy for the elimination of an isopropyl group is reduced from 17,500 to 12,000-14,000 cal/mole, depending on the relative positions of the two alkyl groups. The presence under the conditions of catalytic cracking of this effect, which is associated with the variation in electron density in the benzene nucleus with change in the nature and position of the methyl group, can be regarded as confirmation of the ionic character of the catalytic reactions of hydrocarbons over aluminum silicates.