Thiophosgene

Thiophosgene is a yellow liquid with the formula CSCl₂. This compound has a trigonal planar geometry. It possesses two reactive C-Cl bonds that allow this reagent to be used in diverse procedures related to organic synthesis.

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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.

Safety considerations

CSCl₂ is considered highly toxic.

References

• Dyson, G. M. "Thiophosgene" Organic Syntheses, Coll. Vol. 1, p.506; Vol. 6, p.86.
• Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
• Sharma, S. "Thiophosgene in Organic Synthesis" Synthesis, 1978, pages 804-820.