Journal of Organic Chemistry vol:58 issue:27 pages:7688-7693
The selective formation of allyl-substituted aromatics over acid zeolites by electrophilic substitution of the aromatics with allyl alcohol is reported. In contrast to the reaction in homogeneous phase with H2SO4, this primary product is stable and almost no consecutive reactions of allyl-substitued aromatics are observed. When aryl chloride (7) is used as alkylating agent, nearly no allyl-substituted aromatic is obtained. HCI, liberated during reaction easily isomerizes the double bond, enabling a fast consecutive reaction. This implies that functional selectivity, which is unachievable in homogeneous phase can be easily reached over microporous solid Bronsted acids, provided no homogeneous acid is formed during reaction. The functional selectivity is attributed to the suppression of bimolecular side reactions and to the reduced isomerization rate of the double bond. For the electrophilic aromatic substitution, the turnover number of the acid site is about 120, confirming the true catalytic nature of this reaction. Deactivation of the catalyst is attributed to the oligomerization of an olefin, made upon hydride transfer to an allyl cation.