Thione

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.

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, 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.

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