Sulfonylation of substituted benzenes using Zn-exchanged zeolites

The sulfonylation of substituted benzenes is investigated for Zn-exchanged zeolites (ZSM-5, Y, beta) using two sulfonating agents (methanesulfonyl chloride and benzenesulfonyl chloride). Zinc-exchanged zeolites are significantly more active than their corresponding proton form. Zinc-exchanged zeolites prepared using zinc acetate give higher level of Zn2+ - exchange acid and are more active than those prepared from zinc nitrate. Methanesulfonyl chloride gives similar selectivities for the 2-and 4-substituted products, but benzenesulfonyl chloride gives enhanced selectivity to the 4-product. The highest yields of the 4-product are observed with Zn-H-beta as catalyst. For most zinc-exchanged zeolites no leaching of Zn2+ is observed and furthermore, the Zn2+ that is leached into solution is found to be inactive as a homogeneous catalyst for the reaction. This indicates that the observed reactions are wholly heterogeneously catalysed. The catalytic data are discussed in relation to pore access calculations for the arenium ion intermediates formed during the sulfonylation reaction. (C) 2002 Elsevier Science B.V. All rights reserved.