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Thioketones (also known as thiones or thiocarbonyls) are organosulfur compounds related to conventional ketones. Instead of the formula R2C=O, thioketones have the formula R2C=S, which is reflected by the prefix "thio-" in the name of the functional group. Unhindered alkylthioketones typically tend to form polymers or rings.
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Preparative methods
Thiones are usually prepared from ketones using reagents that exchange S and O atoms. A common reagent is phosphorus pentasulfide and the related reagent Lawesson's reagent. Other methods uses a mixture of hydrogen chloride combined with hydrogen sulfide. Bis(trimethylsilyl)sulfide has also been employed.
Thiobenzophenone ((C6H5)2CS) is a stable deep blue compound that dissolves readily in organic solvents. It photooxidizes in air to benzophenone and sulfur. Since its discovery, a variety of related thiones have been prepared.
Thiosulfines
Thiosulfines, also called thiocarbonyl S-sulfides, are compounds with the formula R2CSS. Although superficially appearing to be cumulenes, with the linkage R2C=S=S, they are more usefully classified as 1,3-dipoles and indeed participate in 1,3-dipolar cycloadditions. Thiosulfines are proposed to exist in equilibrium with dithiiranes, three-membered CS2 rings. Thiosulfines are often invoked as intermediates in mechanistic discussions of the chemistry of thiones. For example, thiobenzophenone decomposes upon oxidation to the 1,2,4-trithiolane (Ph2C)2S3, which arises via the cycloaddition of Ph2CSS to its parent Ph2CS.
Selenoketones
Selenoketones and Telluroketones are the selenium and tellurium analogues of thioketones. They require greater steric and electronic stabilization. Selenobenzophenone reversibly dimerizes. It is known to undergo cycloaddition with 1,3-dienes in a reaction similar to the Diels-Alder reaction.