Organosulfur Compound

any of a group of substances whose molecules contain a carbon-sulfur bond. There are a large number of such compounds, and the compounds are of various types; sulfur, together with hydrogen, oxygen, nitrogen, and the halogens, is one of the principal elements forming organic compounds. The sulfur atom in these compounds can be in any of its characteristic (–2, +4, +6) oxidation states.

There are three main types of organosulfur compounds. The first type (R, R’, and A_r designate organic residues)) contains sulfur atoms in the - 2 oxidation state and includes mercaptans (thioalcohols, RSH), thiophenols (A_rSH), thioaldehydes (R—CH=S), and thioketones (R—CS—R’). Also included here are the thio acids

as well as the various derivatives of these acids, and thioethers (organic sulfides, R—S—R’), disulfides and polysulfides (R—S_x—R’, where x ≥ 2), sulfonium salts (RR’S⁺x^-, where X is an anion, such as Cl^-), such sulfur-containing heterocycles as thiophene, and numerous compounds of various classes that have sulfur-containing groups, such as mercaptoamino acids.

The second type of organosulfur compound contains sulfur atoms in the +4 oxidation state and includes sulfinic acids, which have the structural formula

and sulfoxides (RSOR’). The third type contains sulfur atoms in the + 6 oxidation state and includes sulfonic acids (RSO₃H) and sulfones (R—SO₂—R’).

The principal method for the synthesis of organosulfur compounds involves reactions between organic compounds and either elemental sulfur or the following simple inorganic sulfur compounds: H₂S, Na₂S, NaSH, SCl₂, SO₂, SO₃, and H₂SO₄. The reactions proceed according to the following schemes:

A second important method of synthesis involves mutual inter-conversions of organosulfur compounds.

Organosulfur compounds include such important natural substances as the amino acids cystine and methionine and a series of coenzymes (coenzyme A, lipoic acid), vitamins (thiamine, biotin), and antibiotics (penicillins). The sulfhydryl groups of cystine play an important role in the active site of many enzymes. The disulfide bonds of cysteine, formed as a result of the bonding of two cysteine residues, help support the structure of proteins and peptides. Organosulfur compounds also include many medicinal and physiologically active synthetic substances, such as sulfanilamide drugs, radioprotectors (cystamine, cystaphos), insecticides, fungicides, growth stimulants, poisons (yperite), and various classes of dyes, such as sulfur dyes and certain aniline, anthraquinone, and phthalocya-nine dyes. Certain high-molecular-weight compounds, for example, polysulfide rubbers (Thiokols), may be considered organosulfur compounds. The vulcanization of rubber by sulfur (and sulfur derivatives) is based on the formation of organosulfur compounds. Organosulfur compounds are used as inhibitors of polymerization and oxidation, stabilizers of polymer materials (mercaptobenzimidazole), and solvents (tetramethy-lene sulfone, dimethyl sulfoxide). The salts of organic sulfonic acids are used as surfactants (detergents). Many organosulfur compounds, for example, aromatic sulfonic acids, are important intermediates in heavy organic synthesis.