1911 Encyclopædia Britannica/Mercaptans

MERCAPTANS (Thio-alcohols), organic chemical compounds of the type R.SH (R＝an alkyl group). The name is derived from mercurium captans, in allusion to the fact that these compounds react readily with mercuric oxide to form crystalline mercury derivatives. The mercaptans may be prepared by the action of the alkyl halides on an alcoholic solution of potassium hydrosulphide; by the reduction of the sulpho-chlorides, e.g. C₂H₅SO₂Cl (chlorides of sulphonic acids), by heating the salts of esters of sulphuric acid with potassium hydrosulphide, and by heating the alcohols with phosphorus pentasulphide. They are colourless liquids, which are insoluble in water and possess a characteristic offensive smell. On oxidation by nitric acid they yield sulphonic acids. They combine with aldehyde’s and ketones, with elimination of water and formation of mercaptals and mercaptols. (See Sulphonal.)

Methyl mercaptan, CH₃.SH, is a liquid which boils at 5·8° C. (752 mm.), and forms a crystalline hydrate with water. Ethyl mercaptan, C₂H₅.SH, is a colourless liquid which boils at 36·2° C. It is used commercially in the preparation of sulphonal (q.v.). The mercury salt, Hg(SC₂H₅)₂, crystallizes from alcohol in plates. When heated with alcohol to 190° C. it decomposes into mercury and ethyldisulphide.