Thiophosgene

Thiophosgene is a red liquid with the formula CSCl₂. It is a molecule with trigonal planar geometry. There are two reactive C–Cl bonds that allow it to be used in diverse organic syntheses.

Typically, CSCl₂ is prepared in a two-step process from carbon disulfide. In the first step, carbon disulfide is chlorinated to give trichloromethanesulfenyl chloride (CCl₃SCl), a rare sulfenyl chloride:

The chlorination must be controlled as excess chlorine converts trichloromethanesulfenyl chloride into carbon tetrachloride. Steam distillation separates the trichloromethanesulfenyl chloride and hydrolyzes the disulfur dichloride. Reduction of trichloromethanesulfenyl chloride with, e.g., tin or dihydroanthracene produces thiophosgene:

An alternative one-step reaction is

CSCl₂ is mainly used to prepare compounds with the connectivity CSX₂ where X = OR, NHR. Such reactions proceed via intermediate such as CSClX. Under certain conditions, one can convert primary amines into isothiocyanates. CSCl₂ also serves as a dienophile to give, after reduction 5-thiacyclohexene derivatives. Thiophosgene is also known as the appropriate reagent in Corey-Winter synthesis for stereospecific conversion of 1,2-diols into alkenes.

It forms a head-to-tail dimer upon irradiation with UV light:

Unlike thiophosgene monomer, a red liquid, the photodimer, an example of a 1,3-dithietane, is a colourless solid. Swarts fluorination of the dimer and then cracking is the principal route to thiocarbonyl fluoride.

Thiophosgene decomposes at 200 °C or above to form carbon disulfide and carbon tetrachloride. It has also been observed decomposing to hydrogen sulfide, hydrogen chloride, and carbonyl sulfide gases via contact with human tissue.^{[failed verification]}