Thiourea (//) is an organosulfur compound with the formula SC(NH2)2. It is structurally similar to urea, except that the oxygen atom is replaced by a sulfur atom, but the properties of urea and thiourea differ significantly. Thiourea is a reagent in organic synthesis. "Thioureas" refers to a broad class of compounds with the general structure (R1R2N)(R3R4N)C=S. Thioureas are related to thioamides, e.g. RC(S)NR2, where R is methyl, ethyl, etc.
|Preferred IUPAC name
3D model (JSmol)
|Molar mass||76.12 g/mol|
|Melting point||182 °C (360 °F; 455 K)|
|142 g/l (25 °C)|
|×10−5 cm3/mol −4.24|
|Carc. Cat. 3|
Repr. Cat. 3
Dangerous for the environment (N)
|R-phrases (outdated)||R22, R40, R51/53, R63|
|S-phrases (outdated)||(S2), S36/37, S61|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Structure and bondingEdit
Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å. The weakening of the C-S bond by C-N pi-bonding is indicated by the short C=S bond in thiobenzophenone, which is 1.63 Å.
Thiourea occurs in two tautomeric forms, of which the thione form predominates in aqueous solutions. The equilibrium constant has been Keq is ×10−3. 1.04 The thiol form, which is also known as an isothiourea, can be encountered in substituted compounds such as isothiouronium salts.
The global annual production of thiourea is around 10,000 tonnes. About 40% is produced in Germany, another 40% in China, and 20% in Japan. Thiourea can be produced from ammonium thiocyanate, but more commonly it is produced by the reaction of hydrogen sulfide with calcium cyanamide in the presence of carbon dioxide.
Other industrial uses of thiourea include production of flame retardant resins, and vulcanization accelerators.
Thiourea is used as an auxiliary agent in diazo paper, light-sensitive photocopy paper and almost all other types of copy paper.
It is also used to tone silver-gelatin photographic prints.
Thiourea is used in the Clifton-Phillips and Beaver bright and semi-bright electroplating processes. It is also used in a solution with tin(II) chloride as an electroless tin plating solution for copper printed circuit boards.
Thiourea is also used in the reductive workup of ozonolysis to give carbonyl compounds. Dimethyl sulfide is also an effective reagent for this reaction, but it is highly volatile (boiling point ) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity). 37 °C
Source of sulfideEdit
Thiourea is employed as a source of sulfide, such as for converting alkyl halides to thiols. The reaction capitalizes on the high nucleophilicity of the sulfur center and easy hydrolysis of the intermediate isothiouronium salt:
- CS(NH2)2 + RX → RSC(NH
+ 2 NaOH → RSNa + OC(NH2)2 + NaX
- RSNa + HCl → RSH + NaCl
- C2H4Br2 + 2 SC(NH2)2 → [C2H4(SC(NH2)2)2]Br2
- [C2H4(SC(NH2)2)2]Br2 + 2 KOH → C2H4(SH)2 + 2 OC(NH2)2 + 2 KBr
- Hg2+ + SC(NH2)2 + H2O → HgS + OC(NH2)2 + 2 H+
Precursor to heterocyclesEdit
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.
According to the label on the consumer product, the liquid silver cleaning product TarnX contains thiourea, a detergent, and sulfamic acid. A lixiviant for gold and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting.
- Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: Royal Society of Chemistry. 2014. pp. 98, 864. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
- "Thiourea". Oxford Dictionaries. Oxford University Press. Retrieved 2016-01-21.
- "Thiourea". Merriam-Webster Dictionary. Retrieved 2016-01-21.
- D. Mullen; E. Hellner (1978). "A Simple Refinement of Density Distributions of Bonding Electrons. IX. Bond Electron Density Distribution in Thiourea, CS(NH2)2, at 123K". Acta Crystallogr. B34: 2789–2794. doi:10.1107/S0567740878009243.
- Allegretti, P.E; Castro, E.A; Furlong, J.J.P (March 2000). "Tautomeric equilibrium of amides and related compounds: theoretical and spectral evidences". Journal of Molecular Structure: THEOCHEM. 499 (1–3): 121–126. doi:10.1016/S0166-1280(99)00294-8.
- Bernd Mertschenk; Ferdinand Beck; Wolfgang Bauer (2002). "Thiourea and Thiourea Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a26_803.
- 81st Universal Metal Finishing Guidebook. Metal Finishing Magazine. Fall 2013. p. 285. ISSN 0026-0576.
- C. Kaneko; A. Sugimoro & S. Tanaka (1974). "A facile one-step synthesis of cis-2-cyclopentene and cis-2-cyclohexene-1,4-diols from the corresponding cyclodienes". Synthesis. 1974 (12): 876–877. doi:10.1055/s-1974-23462.
- Gupta, D., Soman, G., and Dev, S. (1982). "Thiourea, a convenient reagent for the reductive cleavage of olefin ozonolysis products". Tetrahedron. 38 (20): 3013–3018. doi:10.1016/0040-4020(82)80187-7.CS1 maint: Multiple names: authors list (link)
- Speziale, A. J. (1963). "Ethanedithiol". Organic Syntheses.; Collective Volume, 4, p. 401
- Liang, Y.; et, al. (2016). "An efficient precursor to synthesize various FeS2 nanostructures via a simple hydrothermal synthesis method". CrystEngComm. 18: 6262–6271.
- Bao, N.; et al. (2007). "Facile Cd−Thiourea Complex Thermolysis Synthesis of Phase-Controlled CdS Nanocrystals for Photocatalytic Hydrogen Production under Visible Light". The Journal of Physical Chemistry C. 111: 17527–17534.
- Foster, H. M., and Snyder, H. R. (1963). "4-Methyl-6-hydroxypyrimidine". Organic Syntheses.CS1 maint: Multiple names: authors list (link); Collective Volume, 4, p. 638
- Dodson, R. M. & King, L. C. (1945). "The reaction of ketones with halogens and thiourea". J. Am. Chem. Soc. 67 (12): 2242–2243. doi:10.1021/ja01228a059. PMID 21005695.
- Anthony Esposito. "Peñoles, UAM unveil pilot thiourea Au-Ag leaching plant - Mexico". Business News Americas (July 13, 2007).