Disulphide

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).

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.