 | |
 | |
| Names | |
|---|---|
| Preferred IUPAC name Thiourea[1] | |
| Other names Thiocarbamide | |
| Identifiers | |
| |
3D model (JSmol) | |
| 605327 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
|
| ECHA InfoCard | 100.000.494 |
| 1604 | |
| KEGG |
|
| RTECS number |
|
| UNII | |
| UN number | 2811 |
| |
| |
| 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 | Urea Selenourea |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Thiourea (/ˌθaɪ.oʊjʊəˈriː.ə,-ˈjʊəri-/)[2][3] is anorganosulfur compound with theformulaSC(NH2)2 and thestructureH2N−C(=S)−NH2. It is structurally similar tourea (H2N−C(=O)−NH2), with theoxygen atom replaced bysulfur atom (as implied by thethio- prefix). The properties of urea and thiourea differ significantly. Thiourea is areagent inorganic synthesis.Thioureas are a broad class of compounds with the formulaSC(NHR)(NH2), SC(NHR)2, etc
Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å.[4] The weakening of the C-S bond by C-N pi-bonding is indicated by the short C=S bond inthiobenzophenone, which is 1.63 Å.
Thiourea occurs in twotautomeric forms, of which thethione form predominates in aqueous solutions. Theequilibrium constant has been calculated asKeq is1.04×10−3.[5] Thethiol form, which is also known as an isothiourea, can be encountered in substituted compounds such asisothiouronium salts.
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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 is manufactured by the reaction ofhydrogen sulfide withcalcium cyanamide in the presence ofcarbon dioxide.[6]
Thioureaper se has few applications. It is mainly consumed as a precursor tothiourea dioxide, which is a common reducing agent in textile processing.[6]
Recently thiourea has been investigated for its multiple desirable properties as afertilizer especially under conditions of environmental stress.[7] It may be applied in various capacities, such as a seed pretreatment (for priming), foliar spray or medium supplementation.
Other industrial uses of thiourea include production of flame retardant resins, andvulcanization accelerators. Thiourea is building blocks topyrimidine derivatives. Thus, thioureas condense with β-dicarbonyl compounds.[8] The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine. The pharmaceuticalsthiobarbituric acid andsulfathiazole are prepared using thiourea.[6]4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea andhydrazine.
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 (seeSepia Toning).
Thiourea is used in the Clifton-Phillips and Beaver bright and semi-bright electroplating processes.[9] It is also used in a solution with tin(II) chloride as an electroless tin plating solution for copperprinted circuit boards.
Thioureas are used (usually ashydrogen-bond donor catalysts) in a research theme calledthiourea organocatalysis.[10] Thioureas are often found to be stronger hydrogen-bond donors (i.e., more acidic) thanureas.[11][12]
Thiourea exists in dynamic equilibrium with ammonium thiocyanate at 150 °C. This equilibrium was once exploited as a route to thiourea, but the separation of the mixture is problematic.[6]
Thiourea reduces peroxides to the correspondingdiols.[13] The intermediate of the reaction is an unstableendoperoxide.
Thiourea is also used in the reductive workup ofozonolysis to givecarbonyl compounds.[14]Dimethyl sulfide is also an effective reagent for this reaction, but it is highly volatile (boiling point 37 °C) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity).
Thiourea is employed as a source of sulfide, such as for convertingalkyl halides to thiols. The reaction capitalizes on the highnucleophilicity of the sulfur center and easy hydrolysis of the intermediateisothiouronium salt:
In this example,ethane-1,2-dithiol is prepared from1,2-dibromoethane:[15]
Like otherthioamides, 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:
These sulfiding reactions, which have been applied to the synthesis of many metal sulfides, require water and typically some heating.[16][17]
Thioureas are building blocks topyrimidine derivatives. Thus thioureas condense with β-dicarbonyl compounds.[18] 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.[19]
The pharmaceuticalsthiobarbituric acid andsulfathiazole are prepared using thiourea.[6]4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea andhydrazine.
According to the label on consumer productsTarnX[20] andSilver Dip,[21] the liquid silver cleaning products contain thiourea along with a warning that thiourea is a chemical onCalifornia's list of carcinogens.[22] Alixiviant for gold and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting.[23]
Thiourea is an essential reagent in theKurnakov test used to differentiatecis- and trans- isomers of certain square planarplatinum complexes. The reaction was discovered in 1893 by Russian chemistNikolai Kurnakov and is still performed as an assay for compounds of this type.[24]
TheLD50 for thiourea is125 mg/kg for rats (oral).[25]
Agoitrogenic effect (enlargement of the thyroid gland) has been reported for chronic exposure, reflecting the ability of thiourea to interfere with iodide uptake.[6]
A cyclic derivative of thiourea calledThiamazole is used to treat overactive thyroid
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