Disulfide

In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. The disulfide anion is S₂²⁻. The term disulfide can also refer to a chemical compound that contains a disulfide center, such as diphenyl disulfide, C₆H₅S-SC₆H₅.

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 disulfides, sulfur is only reduced to a state with oxidation number −1. Its configuration then resembles that of chlorine and, like it, has the tendency to form a covalent bond with another S⁻ ion to form a disulfide (S₂)²⁻ group. Oxygen can also do this; e.g. in peroxides such as H₂O₂. In many cases, each of the two 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. The tendency is a bit more elaborate in the case of sulfur, which can form polysulfides.

Some examples

• Iron disulfide (FeS₂), known as the mineral pyrite.
• Disulfur dichloride (S₂Cl₂), a distillable liquid.
• The amino acid cystine
• The vitamin lipoic acid
• Diphenyl disulfide (Ph₂S₂).

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

See also

• Disulfide bond
• Diphenyl disulfide

References