Mercaptans

Mercaptans (thioalcohols), compounds analogous to alcohols, but containing a sulfhydryl group (-SH) instead of a hydroxyl group, for example CH₃-SH; C₂H₅-SH (methyl- and ethyl-mercaptans). Mercaptans possess an offensive odor, are slightly soluble in water, soluble in alcohol and ether, and in caustic alkalis, forming in the latter case mercaptides of the type R-S-Na. Mercaptans combine with salts of heavy metals, for example Cu, Pb; from the ability to easily combine with salts of Hg [for example (C₂H₅S)₂Hg] mercaptans received their name (corpus mercurio aptum). When acted upon by weak oxidizing agents, mercaptans yield disulfides, for example C₂H₅-S-S-C₂H₅; when acted upon by strong oxidizing agents, sulfonic acids are obtained from mercaptans: C₂H₅.SH+3O=C₂H₅-SO₂-OH. Mercaptans are obtained by the action of acid potassium sulfite on haloalkyls, esters of sulfuric acid, as well as by the reduction of sulfonic acids or their chlorides, by the action of P₂S₅ on alcohols: CH₃J+KSH=CH₃-SH+KJ; C₂H₅-OSO₂-OK+ KSH = C₂H₅SH + K₂SO₄; C₂H₅-SO₂-OH + P₂= = C₂H₅-SH + 3H₂O; 5C₂H₅-OH + P₂S₅ = P₂O₅ + 5C₂H₅-SH. Mercaptans are formed during the putrefaction of protein substances due to the sulfur-containing components of the protein molecule (cystine, cysteine); therefore methyl mercaptan is found in intestinal gases and excreta. It is found in urine after eating asparagus, cabbage, and is also formed when proteins are heated with caustic potash to 250°, with water in a sealed tube to 150°. Butyl mercaptan, C₄H₉SH, is found in the secretion of the stink gland. For the detection of mercaptans, their odor and the ability to give a green color with isatinic acid can be used. The isolation and determination of mercaptans are based on their volatility and the difficult solubility of their compounds with mercury and lead.