Thioketones

Thioketones are organosulfur compounds characterized by a thiocarbonyl group, R2C=S, in which sulfur replaces the oxygen of a carbonyl group. They are the sulfur analogues of ketones and share a similar carbon framework, but the C=S bond imparts different reactivity and properties.

In thioketones the carbon is double-bonded to sulfur and bonded to two substituents, typically aryl or alkyl groups. The C=S bond is longer and more polarizable than C=O, and sulfur’s larger size influences both stability and reactivity. They are commonly named as eponymous thiones or thioketones, with typical examples described as alkyl/aryl thioketones.

Most thioketones are prepared by thionation of carbonyl compounds. Reagents such as Lawesson’s reagent and phosphorus pentasulfide (P4S10) convert ketones into corresponding thioketones while preserving the carbon skeleton. Other approaches include thionation of aldehydes or rearrangements of sulfur-containing precursors. The parent diphenylthioketone, also known as benzophenone thione, is a well-known representative.

Reactivity of thioketones centers on the thiocarbonyl C=S bond. They can undergo nucleophilic addition at carbon, engage in cycloaddition and other pericyclic processes with dienes or dipoles, and serve as intermediates in the construction of sulfur-containing heterocycles. Thioketones are generally more reactive toward certain nucleophiles than their oxygen analogues and are prone to oxidation or desulfurization under demanding conditions.

Applications include use as synthetic intermediates for preparing thioethers, thiols, and sulfur-containing heterocycles; they also function as motifs in catalysis and materials chemistry. A classic example is benzophenone thione, which has served as a model system in thioketone chemistry.