Thiourea dioxide
{{chembox
| Verifiedfields = changed
| verifiedrevid =
| ImageFile = SURDOX.png
| ImageFile1 = Thiox sample.jpg
| PIN = Amino(imino)methanesulfinic acid
| OtherNames = Thiourea dioxide, DegaFAS, Reducing Agent F, Depilor, Formamidine Sulfinic Acid
| Section1 = {{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 1758-73-2
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 42BWR07L73
| PubChem = 61274
| SMILES = C(=N)(N)S(=O)O
| ChemSpiderID = 55213
| StdInChI = 1S/CH4N2O2S/c2-1(3)6(4)5/h(H3,2,3)(H,4,5)
| StdInChIKey = FYOWZTWVYZOZSI-UHFFFAOYSA-N
}}
| Section2 = {{Chembox Properties
| C=1|H=4|N=2|O=2|S=1
| Appearance = White powder
| Density =
| MeltingPtC = 126
| BoilingPt =
| Solubility = 3.0 g/100 mL
}}
| Section3 = {{Chembox Hazards
| FlashPt =
| AutoignitionPt =
| GHSPictograms = {{GHS02}}{{GHS05}}{{GHS07}}{{GHS08}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|H252|H302|H332|H315|H318|H335|H373}}
| PPhrases = {{P-phrases|270|280|235+410|310|305+351+338|407|501}}
}}
}}
Thiourea dioxide or thiox is an organosulfur compound that is used in the textile industry.{{cite encyclopedia|first=Klaus|last=Fischer|title=Textile Auxiliaries|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|year=2003|publisher=Wiley-VCH|url=https://books.google.com/books?id=YH1UAAAAMAAJ|location=Weinheim|doi=10.1002/14356007.a26_227|oclc=55738480|isbn=9783527303854|access-date=2022-06-18|archive-date=2022-06-18|archive-url=https://web.archive.org/web/20220618155203/https://www.google.co.in/books/edition/Ullmann_s_Encyclopedia_of_Industrial_Che/YH1UAAAAMAAJ?hl=en|url-status=live|url-access=subscription}} It functions as a reducing agent.{{cite book|last=Milne|first=George W. A.|url=https://books.google.com/books?id=9vNTAAAAMAAJ|title=Gardner's Commercially Important Chemicals: Synonyms, Trade Names, and Properties|publisher=Wiley-Interscience|oclc=57392953|date=11 July 2005|isbn=9780471735182|location=Hoboken, New Jersey, USA|doi=10.1002/0471736627.ch1|access-date=18 June 2022|archive-date=18 June 2022|archive-url=https://web.archive.org/web/20220618153138/https://www.google.co.in/books/edition/Gardner_s_Commercially_Important_Chemica/9vNTAAAAMAAJ?hl=en&gbpv=0|url-status=live}} It is a white solid, and exhibits tautomerism in solution.{{cite journal |doi=10.1002/chem.201403453 |title=Recent Developments in the Chemistry of Thiourea Oxides |date=2014 |last1=Makarov |first1=Sergei V. |last2=Horváth |first2=Attila K. |last3=Silaghi-Dumitrescu |first3=Radu |last4=Gao |first4=Qingyu |journal=Chemistry – A European Journal |volume=20 |issue=44 |pages=14164–14176 }}
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.{{cite journal |author1=Sullivan, R. A. L. |author2=Hargreaves, A. | title = The Crystal and Molecular Structure of Thiourea Dioxide | journal = Acta Crystallographica | year = 1962 | volume = 15 | issue = 7 | pages = 675–682 | doi = 10.1107/S0365110X62001851| doi-access = free |bibcode=1962AcCry..15..675S }}{{cite journal|title=Reinvestigation of the Structure of Thiourea S,S-Dioxide, CH4N2O2S|author1=Chen, I-C. |author2=Wang, Y.|year=1984|volume=40|pages=1937–1938|doi=10.1107/S010827018401012X|journal=Acta Crystallographica|issue=11 |bibcode=1984AcCrC..40.1937C }} 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. 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.{{cite journal|title=Recent Trends in the Chemistry of Sulfur-Containing Reducing Agents|author=Makarov, S. V.|journal= Russian Chemical Reviews|year=2001|volume=70|issue=10|pages=885–895|doi=10.1070/RC2001v070n10ABEH000659|bibcode=2001RuCRv..70..885M|s2cid=250741549 }}
Synthesis
Thiourea dioxide was first prepared in 1910 by the English chemist Edward de Barry Barnett.Barnett first prepared thiourea dioxide ("aminoiminomethanesulphinic acid") by oxidizing thiourea ("thiocarbamide") with hydrogen peroxide ("hydrogen dioxide"). See: Barnett, Edward de Barry (1910) [https://babel.hathitrust.org/cgi/pt?id=mdp.39015067129042;view=1up;seq=85 "The action of hydrogen dioxide on thiocarbamides,"] {{Webarchive|url=https://web.archive.org/web/20200606074148/https://babel.hathitrust.org/cgi/pt?id=mdp.39015067129042&view=1up&seq=85 |date=2020-06-06 }} Journal of the Chemical Society, Transactions, 97 : 63–65.
Thiourea dioxide is prepared by the oxidation of thiourea with hydrogen peroxide.D. Schubart "Sulfinic Acids and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a25_461}}
:(NH2)2CS + 2H2O2 → (NH)(NH2)CSO2H + 2H2O
The mechanism of the oxidation has been examined.{{cite journal | last1 = Hoffmann | first1 = Michael | last2 = Edwards | first2 = John O. | year = 1977 | title = Kinetics and Mechanism of the Oxidation of Thiourea and N,N'-dialkylthioureas by Hydrogen Peroxide | journal = Inorganic Chemistry | volume = 16 | issue = 12 | pages = 3333–3338 | doi = 10.1021/ic50178a069}} 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.{{US patent reference
| number = 2783272
| y = 1957
| m = 2
| d = 26
| inventor = James H. Young
| title = PRODUCTION OF FORMAMIDINE SULFINIC ACID
}} It can also be prepared by oxidation of thiourea with chlorine dioxide.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}} The quality of the product can be assessed by titration with indigo.
Uses
Thiourea dioxide is used in reductive bleaching in textiles.{{cite journal | author1 = Hebeish, A. |author2=El-Rafie, M. H. |author3=Waly, A. |author4=Moursi, A. Z. | title = 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 = Journal of Applied Polymer Science | year = 1978 | volume = 22 | pages = 1853–1866 | doi = 10.1002/app.1978.070220709 | issue = 7}} Thiourea dioxide has also been used for the reduction of aromatic nitroaldehydes and nitroketones to nitroalcohols.{{cite journal |last1=Sambher |first1=Shikha |last2=Baskar |first2=Chinnappan |last3=Dhillon |first3=Ranjit S. |title=Chemoselective reduction of carbonyl groups of aromatic nitro carbonyl compounds to the corresponding nitroalcohols using thiourea dioxide |journal=Arkivoc |date=22 May 2009 |volume=2009 |issue=10 |pages=141–145 |doi=10.3998/ark.5550190.0010.a14|doi-access=free |hdl=2027/spo.5550190.0010.a14 |hdl-access=free }}