Heteropoly acids as heterogeneous catalysts for thioacetalization and transthioacetalization reactions

Heteropoly acids are effective solid catalysts for the thioacetalization of carbonyl compounds, Tungstophosphoric acid (H3PW12O40), was found to be an effective and a highly selective catalyst for the thioacetalization of aldehydes, ketones and for the transthioacetalization of acetals, acylals and O,S-acetals which proceeded in excellent yields in the absence of solvent. The catalyst has also been successfully applied to the chemoselective conversion of alpha- or beta-diketones and a beta-keto ester into the corresponding dithioacetals. Sterically hindered carbonyl compounds such as camphor and benzophenone were also converted to their corresponding thioacetals in refluxing petroleum ether in 89-94% yields. Surprisingly, anthrone was reduced to anthracene in 91% yield.