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

• Aliphatic and aromatic thiols are S-acylated with carboxylic acids or their esters.
• The gas-phase catalysis proceeds above 200 °C without any solvents or additives.
• Brønsted acid sites of halide clusters catalyze the reaction.
• Silica–alumina, zeolites, and heteropoly acids also catalyze the reaction.
• Thermal stability above 200 °C is a prerequisite for the catalyst.

Benzenethiol is reacted with acetic acid in a hydrogen stream over [(Mo6Cl8)Cl4(H2O)2]·6H2O. Catalytic activity of the clusters appears above 200 °C, yielding S-phenyl thioacetate. The selectivity is 98% at 300 °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)Cl2(H2O)4]·4H2O at 450 °C, the sterically unhindered moiety of the ester is incorporated into the products: S-phenyl thioacetate or methyl phenyl sulfide is obtained selectively. A Brønsted 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 °C also catalyze these reactions.

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