Sulfur dichloride

Sulfur dichloride is the chemical compound with the formula SCl₂. This cherry-red liquid is the simplest and one of two common sulfur chlorides. It is used as a precursor to organosulfur compounds.^[1]

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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 + 4Cl₂ → 4S₂Cl₂; ΔH = −58.2 kJ/mol

S₂Cl₂ + Cl₂ → 2SCl₂; 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^[2] and ethylene to give sulfur mustard S(CH₂CH₂Cl)₂.^[3]

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.

References

1. ^ Schmidt, M.; Siebert, W. "Sulphur" Comprehensive Inorganic Chemistry Vol. 2, ed. A.F. Trotman-Dickenson. 1973.
2. ^ Bishop, R. "9-Thiabicyclo[3.3.1]nonane-2,6-dione" Organic Syntheses, Collected Volume 9, p.692 (1998). http://www.orgsyn.org/orgsyn/pdfs/CV9P0692.pdf
3. ^ R. J. Cremlyn “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0 471 95512 4.