S-Acylation of aliphatic and aromatic thiols with carboxylic acids and their esters over solid acid catalysts in the gas phase at temperatures above 200°C

Benzenethiol is reacted with acetic acid in a hydrogen stream over [(Mo6Cl8)Cl-4(H2O)(2)]center dot 6H(2)O. Catalytic activity of the clusters appears above 200 degrees C, yielding S-phenyl thioacetate. The selectivity is 98% at 300 degrees C. Niobium, tantalum, and tungsten halide clusters with the same octahedral metal framework also catalyze the reaction. Benzoic acid and aliphatic carboxylic acids afford the corresponding S-phenyl carbothioates by reaction with benzenethiol. Aliphatic thiols are also S-acylated to yield the corresponding S-alkyl carbothioates. When carboxylic esters are applied to the reaction with benzenethiol over [(Nb6Cl12)Cl-2(H2O)(4)]center dot 4H(2)O at 450 degrees C, the sterically unhindered moiety of the ester is incorporated into the products: S-phenyl thioacetate or methyl phenyl sulfide is obtained selectively. A Bronsted acid site developed on the cluster complex by thermal activation is the active site of the catalyst. Hence, solid acids such as silica-alumina, zeolites, and heteropoly acids that are stable above 200 degrees C also catalyze these reactions. (C) 2013 Elsevier B.V. All rights reserved.