Thioureas


Thioureas are members of a family of organosulfur compounds with the formula SC2. The parent member of this class of compounds is thiourea SC2. The thiourea functional group has a planar CSN2 core.
is a thiourea derivative used as an antithyroid drug.

Structure and bonding

Thioureas have planar N2CS core. The C=S bond distance is near 1.71 Å, which is 0.1 Å longer than in normal ketones. The C-N distances are short. Thioureas occurs in two tautomeric forms. For the parent thiourea, the thione form predominates in aqueous solutions. The thiol form, known as an isothiourea, can be encountered in substituted compounds such as isothiouronium salts.

Synthesis

N,N′-unsubstituted thioureas can be prepared by treating the corresponding cyanamide with hydrogen sulfide or similar sulfide sources. Organic ammonium salts react with potassium thiocyanate as the source of the thiocarbonyl.
Alternatively, N,N′-disubstituted thioureas can be prepared by coupling two amines with thiophosgene:
Amines also condense with organic thiocyanates to give thioureas:
Cyclic thioureas are prepared by transamidation of thiourea with diamines. Ethylene thioureais synthesized by treating ethylenediamine with carbon disulfide. In some cases, thioureas can be prepared by thiation of ureas using phosphorus pentasulfide.
is an excellent accelerant of vulcanization of neoprene and polychloroprene rubbers.

Applications

Precursor to heterocycles

Thioureas are building blocks to pyrimidine derivatives. Thus thioureas condense with β-dicarbonyl compounds. The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine. The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine.

Catalysis

Some thioureas are vulcanization accelerators. Thioureas are also used in a research theme called thiourea organocatalysis.