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=CS(O)(OH), named formamidine sulfinic acid.[6]
Structure of the sulfinic acid tautomer of thiourea dioxide, as exists in aqueous solution
Synthesis
Thiourea dioxide was first prepared in 1910 by the English chemist Edward de Barry Barnett.[7]
The mechanism of the oxidation has been examined.[9] An aqueous solution of thiourea dioxide has a pH about 6.5 at which thiourea dioxide is hydrolyzed to urea and sulfoxylic acid. It has been found that at pH values of less than 2, thiourea and hydrogen peroxide react to form a disulfide species. It is therefore convenient to keep the pH between 3 and 5 and the temperature below 10 °C.[10] It can also be prepared by oxidation of thiourea with chlorine dioxide.[11] The quality of the product can be assessed by titration with indigo.[8]
↑ Makarov, Sergei V.; Horváth, Attila K.; Silaghi-Dumitrescu, Radu; Gao, Qingyu (2014). "Recent Developments in the Chemistry of Thiourea Oxides". Chemistry – A European Journal. 20 (44): 14164–14176. doi:10.1002/chem.201403453.
↑ Barnett first prepared thiourea dioxide ("aminoiminomethanesulphinic acid") by oxidizing thiourea ("thiocarbamide") with hydrogen peroxide ("hydrogen dioxide"). See: Barnett, Edward de Barry (1910) "The action of hydrogen dioxide on thiocarbamides,"Archived 2020-06-06 at the Wayback MachineJournal of the Chemical Society, Transactions, 97: 63–65.
1 2 D. Schubart "Sulfinic Acids and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH, Weinheim. doi:10.1002/14356007.a25_461
↑ Hoffmann, Michael; Edwards, John O. (1977). "Kinetics and Mechanism of the Oxidation of Thiourea and N,N'-dialkylthioureas by Hydrogen Peroxide". Inorganic Chemistry. 16 (12): 3333–3338. doi:10.1021/ic50178a069.
↑ USpatent 2783272,James H. Young,"PRODUCTION OF FORMAMIDINE SULFINIC ACID",issued 1957-2-26
↑ Rábai, G.; Wang, R. T.; Kustin, Kenneth (1993). "Kinetics and mechanism of the oxidation of thiourea by chlorine dioxide" International Journal of Chemical Kinetics. Volume 25: 53–62. doi:10.1002/kin.550250106
↑ Hebeish, A.; El-Rafie, M. H.; Waly, A.; Moursi, A. Z. (1978). "Graft copolymerization of vinyl monomers onto modified cotton. IX. Hydrogen peroxide–thiourea dioxide redox system induced grafting of 2-methyl-5-vinylpyridine onto oxidized celluloses". Journal of Applied Polymer Science. 22 (7): 1853–1866. doi:10.1002/app.1978.070220709.
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