Acylation of biphenyl with acetic anhydride and carboxylic acids over zeolite catalysts

Abstract

Acylation of biphenyl with acetic anhydride and carboxylic acids over zeolite catalysts is investigated. Acylation of biphenyl with acetic anhydride over zeolite HY and zeolite beta at 83°C gives 4-acetylbiphenyl as the main product. The selectivity to 4-acetylbiphenyl is always higher than 98% and the highest yields are obtained over zeolite beta. An increase of the Si/Al ratio in zeolite beta leads to slightly higher rates of 4-acetylbiphenyl formation, however, the final yields are always within the range 8–10%. Catalyst deactivation occurs and is mainly due to product inhibition, i.e. 4-acetylbiphenyl strongly competes for the adsorption sites on the zeolite. Acylation of 4-acetylbiphenyl yielded less than 3% diacylated products, with a 4,4′-diacetylbiphenyl selectivity below 12%. Solventless acylation of biphenyl with hexanoic acid at 150°C produces 4-hexanoylbiphenyl (selectivity>98%) at a yield of 8–14% and the best results are obtained over zeolite HY. An increase in temperature enhances the yield of 4-hexanoylbiphenyl (53% at 200°C) but decreases slightly the selectivity (∼92%). Acylation with a bulky acid (trimethylacetic acid) in an attempt to obtain shape selective acylation led to the formation of 4- t-butylbiphenyl as main product (yield ∼9%) instead of the acylated product.