Thiourea
Names | |
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Preferred IUPAC name
Thiourea[1] | |
Other names
Thiocarbamide
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Identifiers | |
3D model (
JSmol ) |
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605327 | |
ChEBI | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard
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100.000.494 |
1604 | |
KEGG | |
PubChem CID
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RTECS number
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UNII | |
UN number | 2811 |
CompTox Dashboard (EPA)
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Properties | |
SC(NH2)2 | |
Molar mass | 76.12 g·mol−1 |
Appearance | white solid |
Density | 1.405 g/mL |
Melting point | 182 °C (360 °F; 455 K) |
142 g/L (25 °C) | |
−4.24×10−5 cm3/mol | |
Hazards | |
GHS labelling: | |
Warning | |
H302, H351, H361, H411 | |
P201, P202, P264, P270, P273, P281, P301+P312, P308+P313, P330, P391, P405, P501 | |
NFPA 704 (fire diamond) | |
Related compounds | |
Related compounds
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Urea Selenourea |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Thiourea (
Structure and bonding
Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å.[5] 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 calculated as Keq is 1.04×10−3.[6] The thiol form, which is also known as an isothiourea, can be encountered in substituted compounds such as isothiouronium salts.
Production
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 manufactured by the reaction of hydrogen sulfide with calcium cyanamide in the presence of carbon dioxide.[7]
- CaCN2 + 3 H2S → Ca(SH)2 + (NH2)2CS
- 2 CaCN2 + Ca(SH)2 + 6 H2O → 2 (NH2)2CS + 3 Ca(OH)2
- Ca(OH)2 + CO2 → CaCO3 + H2O
Applications
Thiox precursor
Thiourea per se has few applications. It is mainly consumed as a precursor to thiourea dioxide, which is a common reducing agent in textile processing.[7]
Fertilizers
Recently thiourea has been investigated for its multiple desirable properties as a fertilizer especially under conditions of environmental stress.[8] It may be applied in various capacities, such as a seed pretreatment (for priming), foliar spray or medium supplementation.
Other uses
Other industrial uses of thiourea include production of flame retardant resins, and vulcanization accelerators. Thiourea is building blocks to pyrimidine derivatives. Thus, thioureas condense with β-dicarbonyl compounds.[9] 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.[7] 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine.
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 (see Sepia Toning).
Thiourea is used in the Clifton-Phillips and Beaver bright and semi-bright electroplating processes.[10] It is also used in a solution with tin(II) chloride as an electroless tin plating solution for copper printed circuit boards.
Thioureas are used (usually as hydrogen-bond donor catalysts) in a research theme called thiourea organocatalysis.[11] Thioureas are often found to be stronger hydrogen-bond donors (i.e., more acidic) than ureas.[12][13]
Reactions
The material has the unusual property of changing to ammonium thiocyanate upon heating above 130 °C. Upon cooling, the ammonium salt converts back to thiourea.[citation needed]
Reductant
Thiourea reduces peroxides to the corresponding
Thiourea is also used in the reductive workup of
Source of sulfide
Thiourea is employed as a source of sulfide, such as for converting
- CS(NH2)2 + RX → RSC(NH2)+2X−
- RSC(NH2)+2X− + 2 NaOH → RSNa + OC(NH2)2 + NaX + H2O
- RSNa + HCl → RSH + NaCl
In this example,
- 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
Like other thioamides, thiourea can serve as a source of sulfide upon reaction with metal ions. For example, mercury sulfide forms when mercuric salts in aqueous solution are treated with thiourea:
- Hg2+ + SC(NH2)2 + H2O → HgS + OC(NH2)2 + 2 H+
These sulfiding reactions, which have been applied to the synthesis of many metal sulfides, require water and typically some heating.[17][18]
Precursor to heterocycles
Thioureas are building blocks to pyrimidine derivatives. Thus thioureas condense with β-dicarbonyl compounds.[19] The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine.
Similarly, aminothiazoles can be synthesized by the reaction of α-haloketones and thiourea.[20]
The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea.[7] 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine.
Silver polishing
According to the label on consumer products TarnX[21] and Silver Dip,[22] the liquid silver cleaning products contain thiourea along with a warning that thiourea is a chemical on California's list of carcinogens.[23] A lixiviant for gold and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting.[24]
Kurnakov reaction
Thiourea is an essential reagent in the Kurnakov test used to differentiate cis- and trans- isomers of certain square planar platinum complexes. The reaction was discovered in 1893 by Russian chemist Nikolai Kurnakov and is still performed as an assay for compounds of this type.[25]
Safety
The LD50 for thiourea is 125 mg/kg for rats (oral).[26]
A goitrogenic effect (enlargement of the thyroid gland) has been reported for chronic exposure, reflecting the ability of thiourea to interfere with iodide uptake.[7]
A cyclic derivative of thiourea called Thiamazole is used to treat overactive thyroid
See also
References
- OCLC 1077224056.
- ^ "thiourea". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 2020-03-22.
- ^ "thiourea". Merriam-Webster.com Dictionary. Retrieved 2016-01-21.
- ^ "thiourea". Dictionary.com Unabridged (Online). n.d.
- .
- .
- ^ ISBN 3527306730.
- (PDF) from the original on 2020-02-15. Retrieved 2020-12-09.
- .
- from the original on 2017-11-17. Retrieved 2016-10-11.
- PMID 14518182.
- PMID 22435999.
- PMID 35322485.
- from the original on 2021-06-12. Retrieved 2022-06-18.
- doi:10.1016/0040-4020(82)80187-7.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - ^ Speziale, A. J. (1963). "Ethanedithiol". Organic Syntheses; Collected Volumes, vol. 4, p. 401.
- .
- .
- ^ Foster, H. M., and Snyder, H. R. (1963). "4-Methyl-6-hydroxypyrimidine". Organic Syntheses
{{cite journal}}
: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 4, p. 638. - PMID 21005695.
- ^ "Tarn-X PRO Tarnish Remover" (PDF). The Betty Mills Company, Inc. Archived (PDF) from the original on 2021-06-06. Retrieved 2021-06-06.
- ^ "Hagerty Silver Dip". J.L. Smith & Co. Archived from the original on 2021-06-06. Retrieved 2021-06-06.
- ^ Expedited Cancer Potency Values and Proposed Regulatory Levels for Certain Proposition 65 Carcinogens (PDF) (Report). April 1992. Archived (PDF) from the original on 2022-01-21. Retrieved 2022-06-18.
- ^ Esposito, Anthony (July 13, 2007). "Peñoles, UAM unveil pilot thiourea Au-Ag leaching plant in Mexico". Business News Americas. Archived from the original on 17 February 2009.
- from the original on 2021-03-28. Retrieved 2020-12-09.
- ^ "Thiourea and its properties". September 11, 1986. Archived from the original on May 27, 2010. Retrieved January 6, 2012.
Further reading
- Patai, Saul (1977). The Chemistry of Double-Bonded Functional Groups. New York, NY: John Wiley & Sons. pp. 1355–1496. OCLC 643207498.