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.

Preparation of CSCl2

CSCl2 is prepared in a two-step process from carbon disulfide. In the first step, carbon disulfide is chlorinated to give trichloromethanesulfenyl chloride, CCl3SCl:
The chlorination must be controlled as excess chlorine converts trichloromethanesulfenyl chloride into carbon tetrachloride. Steam distillation separates the trichloromethanesulfenyl chloride, a rare sulfenyl chloride, and hydrolyzes the sulfur monochloride. Reduction of trichloromethanesulfenyl chloride produces thiophosgene:
Typically, tin is used for the reducing agent M.

Reactions

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 olefins.
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 colorless solid.

Safety considerations

CSCl2 is considered highly toxic.