Sulfur dichloride

Sulfur dichloride is the chemical compound with the formula SCl₂. This cherry-red liquid is the simplest sulfur chloride and one of the most common. It is used as a precursor to organosulfur compounds.

Chlorination of sulfur

SCl₂ is produced by the chlorination of either elemental sulfur. The process occurs in a series of steps, some of which are:

S₈ + 4 Cl₂ → 4 S₂Cl₂; ΔH = −58.2 kJ/mol

S₂Cl₂ + Cl₂ → 2 SCl₂; ΔH = −40.6 kJ/mol

The addition of Cl₂ to S₂Cl₂ has been proposed to proceed via a mixed valence intermediate Cl₃S-SCl. SCl₂ undergoes even further chlorination to give SCl₄, but this species is unstable at near room temperature. It is likely that several S_xCl₂ exist where x > 2.

Disulfur dichloride, S₂Cl₂, is the most common impurity in SCl₂. Separation of SCl₂ from S₂Cl₂ is possible via distillation with PCl₃ to form an azeotrope of 99% purity

Use of SCl₂ in chemical synthesis

• SCl₂ is used in organic synthesis. It adds to alkenes to give chloride-substituted thioethers. Illustrative applications are its addition to 1,5-cyclooctadiene to give a bicyclic thioether and ethylene to give sulfur mustard S(CH₂CH₂Cl)₂.

SCl₂ is also a precursor to several inorganic sulfur compounds. Treatment with fluoride salts gives SF₄. Reaction with ammonia affords sulfur nitrides related to S₄N₄. With H₂S, SCl₂ reacts to give "higher" sulfanes such as S₃H₂.

Safety considerations

SCl₂ hydrolyzes with release of HCl. Old samples contain Cl₂.