Disulfur dichloride

Disulfur dichloride (or disulphur dichloride by the British English spelling) is the inorganic compound of sulfur and chlorine with the formula S₂Cl₂. It is an amber oily liquid.

Sometimes, this compound is incorrectly named sulfur monochloride (or sulphur monochloride by the British English spelling), the name implied by its empirical formula SCl.

S₂Cl₂ has the structure implied by the formula Cl−S−S−Cl, wherein the dihedral angle between the Cl^a−S−S and S−S−Cl^b planes is 85.2°. This structure is referred to as gauche, and is akin to that for H₂O₂. A rare isomer of S₂Cl₂ is S=SCl₂ (thiothionyl chloride); this isomer forms transiently when S₂Cl₂ is exposed to UV-radiation (see thiosulfoxides).

Disulfur dichloride is a yellow liquid that fumes in moist air due to reaction with water:

It is produced by partial chlorination of elemental sulfur. The reaction proceeds at usable rates at room temperature. In the laboratory, chlorine gas is led into a flask containing elemental sulfur. As disulfur dichloride is formed, the contents become a golden yellow liquid:

Excess chlorine produces sulfur dichloride, which causes the liquid to become less yellow and more orange-red:

The reaction is reversible, and upon standing, SCl₂ releases chlorine to revert to the disulfur dichloride. Disulfur dichloride has the ability to dissolve large quantities of sulfur, which reflects in part the formation of dichloropolysulfanes:

Disulfur dichloride can be purified by distillation from excess elemental sulfur.