any of a class of organic compounds containing sulfur and oxygen and having the general formula (RR′) SO, in which R and R′ are a grouping of carbon and hydrogen atoms. The sulfoxides are good solvents for salts and polar compounds.

The best-known sulfoxide is dimethyl (or methyl) sulfoxide (DMSO (dimethyl sulfoxide)), which is prepared by aerial oxidation of dimethyl sulfide (a by-product of paper manufacture) in the presence of nitrogen dioxide. DMSO is used as a solvent in a wide variety of industrial processes, including the manufacture of polyacrylonitrile fibres, the extraction of aromatic hydrocarbons from refinery streams, the manufacture of certain pesticides, for industrial cleaning, and for paint stripping. It is also used as a solvent for drugs and antitoxins applied topically. The last use is based on its remarkable ability to penetrate animal tissues.

Dimethyl sulfoxide is a colourless and odourless liquid, boiling at 189° C (372° F). It is miscible in all proportions with water, alcohol, and most organic solvents.