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.

Synthesis 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:

CS₂ + 3 Cl₂ → CCl₃SCl + S₂Cl₂

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:

CCl₃SCl + M → CSCl₂ + MCl₂

Typically, tin is used for the reducing agent M.

Uses of CSCl₂

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 converting 1,2-diols into olefins.

Safety considerations

CSCl₂ is considered highly toxic.

References

• Dyson, G.M. (1926). "Thiophosgene". Organic Syntheses 6: 86. http://www.orgsyn.org/orgsyn/pdfs/CV1P0506.pdf. Retrieved 21 November 2011. 
• Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
• Sharma, S. (1978). "Thiophosgene in Organic Synthesis". Synthesis 1978 (11): 803. doi:10.1055/s-1978-24896.  edit