disulfide

General structure of disulfides

In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. Disulfide usually refer to a chemical compound that contains a disulfide bond, such as diphenyl disulfide, C₆H₅S-SC₆H₅.

Inorganic vs. organic disulfides

The disulfide anion is S₂²⁻. Sulfur is usually assigned to the reduced oxidation number −2, described as S²⁻ and called sulfide. It has the electron configuration of a noble gas (argon). In disulfide, sulfur is only reduced to a state with oxidation number −1. Its configuration then resembles that of a chlorine atom. It thus tends to form a covalent bond with another S⁻ center to form S₂²⁻ group. Oxygen also behaves analogous, e.g. in peroxides such as H₂O₂. Examples:

• Iron disulfide (FeS₂), e.g. the mineral pyrite.
• Disulfur dichloride (S₂Cl₂), a distillable liquid.

In many cases, each of the sulfur atoms in a disulfide group is covalently bonded to a carbon atom in an organic compound, forming a disulfide bond, sometimes called a disulfide linkage or a disulfide bridge. Examples:

• The amino acid cystine
• The vitamin lipoic acid

FeS2 unit cell	S2Cl2	cystine	lipoic acid	Ph2S2

Misnomers

Disulfide is also used to refer to compounds that contain two sulfide (S²⁻) centers. The compound carbon disulfide, CS₂ is described with the structural formula i.e. S=C=S. This molecule is not a disulfide in the sense that it lacks a S-S bond. Similarly, molybdenum disulfide, MoS₂, is not a disulfide in the sense again that its sulfur atoms are not linked.

CS2	MoS2

References