Thiourea dioxide
Chemical compound
From Wikipedia, the free encyclopedia
Thiourea dioxide or thiox is an organosulfur compound that is used in the textile industry.[1] It functions as a reducing agent.[2] It is a white solid, and exhibits tautomerism in solution.[3]
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| Names | |
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| Preferred IUPAC name
Amino(imino)methanesulfinic acid | |
| Other names
Thiourea dioxide, DegaFAS, Reducing Agent F, Depilor, Formamidine Sulfinic Acid | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.015.598 |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| CH4N2O2S | |
| Molar mass | 108.12 g·mol−1 |
| Appearance | White powder |
| Melting point | 126 °C (259 °F; 399 K) |
| 3.0 g/100 mL | |
| Hazards | |
| GHS labelling: | |
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| Danger | |
| H252, H302, H315, H318, H332, H335, H373 | |
| P235+P410, P270, P280, P305+P351+P338, P310, P407, P501 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure
Crystalline and gaseous thiourea dioxide adopts a C2v-symmetric structure. Selected bond lengths: S-C = 186, C-N = 130, and S-O = 149 pm. The sulfur center is pyramidal. The C-S bond length is close to that of a single bond. For comparison, the C=S bond in thiourea is 171 pm.[4][5] Instead the bonding is described with a significant contribution from a dipolar resonance structure with multiple bonding between C and N. One consequence of this bonding is the planarity of the nitrogen centers.[6] In the presence of water or DMSO, thiourea dioxide converts to the tautomer, a sulfinic acid, (H2N−)(HN=)C−S(=O)(−OH), named formamidine sulfinic acid.[6]
Synthesis
Thiourea dioxide was first prepared in 1910 by the English chemist Edward de Barry Barnett, through a method not dissimilar from the modern synthesis.[7]
Thiourea dioxide is prepared by the oxidation of thiourea with hydrogen peroxide,[8] while maintaining a pH between 3 and 5 and temperature below 10 °C:[9]
- (NH2)2CS + 2 H2O2 → (NH)(NH2)CSO2H + 2 H2O
It can also be prepared by oxidation with chlorine dioxide.[10] The quality of the product can be assessed by titration with indigo.[8]
Properties
Below pH 6.5, thiourea dioxide hydrolyzes to sulfoxylic acid and urea.[9] Further oxidation with a peracid gives the corresponding sulfonic acid.[11]