Transalkylation of Alkylaromatics Other Than Toluene

Weitkemp carried out the disproportionation of ethylbenzene over a variety of catalysts and concluded that this reaction is a valuable test reaction for the characterization of zeolites of unknown structure. Useful criteria are the presence or absence of 

A very high / ara-selectivity of inorganic-modified ZSM-5 was also manifested in the disproportionation of ethylbenzene. The results with ZSM-5 modified with magnesium and phosphorus compounds are shown in Table 4.10. The concentration of ara-isomer in the diethylbenzene products was over 99%.  

The importance of transition state-type selectivity was first demonstrated by Csic-sery. In the reaction of 1-methyl — 2-ethylbenzene over mordenite, the amounts of 1,3-dimethyl — 5-ethylbenzene and 1 -methyl — 3,5-dimethylbenzene were very small where the 1,3,5-trialkylbenzenes are the main components at equilibrium. It was concluded that symmetrical trialkylbenzenes cannot form in the pores of H-mordenite too little space is available for diphenylmethane-type intermediates in transition states leading to symmetriccd isomers. The other trialkylbenzene isomers can form because their transition states are smtiller. 

Transalkylation between isopropylbenzene and benzene to yield n-propylbenzene over ZSM-5 zeolites was reported by Beyer and Borbely.  

Since the transformation of isopropylbenzene to propylbenzene is not effected in the absence of benzene, it is obvious that this side-chain isomerization proceeds via intermolecular alkyl transfer. The transfer occurs below 530 K at LHSV of 11.4, the 50% conversion level is reached at 560 K. 

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