| Thiourea | |
|---|---|
|
Thiourea |
|
|
Other names
Thiocarbamide |
|
| Identifiers | |
| CAS number | 62-56-6 |
| PubChem | 2723790 |
| ChemSpider | 2005981 |
| UNII | GYV9AM2QAG |
| UN number | 2811 |
| KEGG | C14415 |
| ChEMBL | CHEMBL260876 |
| RTECS number | YU2800000 |
| Jmol-3D images | Image 1 |
|
|
|
|
| Properties | |
| Molecular formula | CH4N2S |
| Molar mass | 76.12 g/mol |
| Appearance | white solid |
| Density | 1.405 g/ml |
| Melting point |
182 °C, 455 K, 360 °F |
| Solubility in water | 14.2 g/100ml (25°C) |
| Hazards | |
| MSDS | External MSDS |
| EU Index | 612-082-00-0 |
| EU classification | Carc. Cat. 3 Repr. Cat. 3 Harmful (Xn) Dangerous for the environment (N) |
| R-phrases | R22, R40, R51/53, R63 |
| S-phrases | (S2), S36/37, S61 |
| Related compounds | |
| Related compounds | Urea |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
|
| Infobox references | |
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.
Contents |
Thiourea is a planar molecule. The C=S bond distance is 1.60±0.1 Å for thiourea (as well as many of its derivatives). 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.
Thiourea occurs in two tautomeric forms. In aqueous solution, the thione shown on the left below predominates:
The global annual production of thiourea is around 10,000 tons.[1] About 40% is produced in Germany, another 40% in China, and 20% in Japan. Thiourea is 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.[1]
Many thiourea derivatives are useful. N,N-unsubstituted thioureas are generally prepared by allowing the corresponding cyanamide to react with LiAlHSH in the presence of 1 N HCl in anhydrous diethyl ether. LiAlHSH can be prepared by reacting sulfur with lithium aluminium hydride.[2]
The main application of thiourea is in textile processing.[1]
Thiourea reduces peroxides to the corresponding diols.[3] The intermediate of the reaction is an unstable epidioxide which can only be identified at −100 °C. Epidioxide is similar to epoxide except with two oxygen atoms. This intermediate reduces to diol by thiourea.
Thiourea is also used in the reductive workup of ozonolysis to give carbonyl compounds.[4] Dimethyl sulfide is also an effective reagent for this reaction, but it is highly volatile (b.p. 37 °C) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity).
Thiourea is commonly employed as a source of sulfide, e.g. for converting alkyl halides to thiols. Such reactions proceed via the intermediacy of isothiuronium salts. The reaction capitalizes on the high nucleophilicity of the sulfur center and the hydrolytic instability of the isothiuronium salt:
In this example, ethane-1,2-dithiol is prepared from 1,2-dibromopropane:[5]
Thiourea is a precursor to sulfide to produce metal sulfides, e.g. mercury sulfide, upon reaction with the metal salt in aqueous solution.
Thioureas are used a building blocks to pyrimidine derivatives. Thus thioureas condense with β-dicarbonyl compounds.[6] 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 alpha-halo ketones and thiourea.[7]
The pharmaceuticals thiobarbituric acid and sulfathiazole is prepared using thiourea.
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.[8]
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.
Thioureas are compounds containing the thiourea motif. Examples are sulfathiourea, noxytiolin and Burimamide. Thioureas are catalysts in thiourea organocatalysis.
The LD50 for thiourea is 1 g/kg for rats (oral). A goitrogenic effect (enlargement of the thyroid gland) has been reported for chronic exposure, reflecting the ability of thiourea to interfere with iodide uptake.[1]