Thioureas

Thioureas are members of a family of organosulfur compounds with the formula SC(NR2)2. The parent member of this class of compounds is thiourea SC(NH2)2. The thiourea functional group has a planar CSN2 core.

Methylthiouracil is a thiourea derivative used as an antithyroid drug.

Synthesis

N,N′-unsubstituted thioureas can be prepared by treating the corresponding cyanamide with hydrogen sulfide or similar sulfide sources.[1]

Alternatively, N,N′-disubstituted thioureas can be prepared by coupling two amines with thiophosgene:[2]

2 R2NH + CSCl2 + 2  (R2N)(R′2N)CS + 2 HCl

Amines also condense with organic thiocyanates to give thioureas:[3]

R2NH + R′NCS → (R2N)(HR′N)CS

Cyclic thioureas are prepared by transamidation of thiourea with diamines. Ethylene thioureais synthesized by treating ethylenediamine with carbon disulfide.[4] In some cases, thioureas can be prepared by thiation of ureas using phosphorus pentasulfide.

Ethylene thiourea is an excellent accelerant of vulcanization of neoprene and polychloroprene rubbers.

Applications

Precursor to heterocycles

Thioureas are building blocks to pyrimidine derivatives. Thus thioureas condense with β-dicarbonyl compounds.[5] The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine. The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea.[6] 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine.

Catalysis

Some thioureas are vulcanization accelerators. Thioureas are also used in a research theme called thiourea organocatalysis.[7]

References

  1. ↑ Koketsu, Mamoru; Kobayashi, Chikashi; Ishihara, Hideharu (2003). "Synthesis of N-aryl-S-alkylthiocarbamates". Heteroatom Chemistry. 14: 374–378. doi:10.1002/hc.10163.
  2. ↑ Yi-Bo Huang, Wen-Bin Yi, Chun Cai (2012). "Thiourea Based Fluorous Organocatalyst". Top. Curr. Chem. 308: 191–212. doi:10.1007/128_2011_248.
  3. ↑ Miyabe, H.; Takemoto, Y. (2008). "Discovery and Application of Asymmetric Reaction by Multifunctional Thioureas". Bull Chem Soc Jpn. 81: 785.
  4. ↑ C. F. H. Allen; C. O. Edens; James VanAllan. "Ethylene Thiourea". Organic Syntheses. ; Collective Volume, 3, p. 394
  5. ↑ Foster, H. M., and Snyder, H. R. (1963). "4-Methyl-6-hydroxypyrimidine". Organic Syntheses. ; Collective Volume, 4, p. 638
  6. ↑ Bernd Mertschenk, Ferdinand Beck, Wolfgang Bauer (2002). "Thiourea and Thiourea Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a26_803.
  7. ↑ R. Schreiner, Peter (2003). "Metal-free organocatalysis through explicit hydrogen bonding interactions". Chem. Soc. Rev. 32: 289–296. doi:10.1039/b107298f. PMID 14518182.

Further reading

  • Patai, S., ed. (1977). The Chemistry of double-bonded functional groups. New York, NY: John Wiley & Sons. pp. 1355–1496. ISBN 0-471-92493-8.
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