Thiourea

Revision as of 16:52, 20 August 2012 by WikiBot (talk | contribs) (Robot: Automated text replacement (-{{SIB}} +, -{{EH}} +, -{{EJ}} +, -{{Editor Help}} +, -{{Editor Join}} +))
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

Template:Chembox new

WikiDoc Resources for Thiourea

Articles

Most recent articles on Thiourea

Most cited articles on Thiourea

Review articles on Thiourea

Articles on Thiourea in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Thiourea

Images of Thiourea

Photos of Thiourea

Podcasts & MP3s on Thiourea

Videos on Thiourea

Evidence Based Medicine

Cochrane Collaboration on Thiourea

Bandolier on Thiourea

TRIP on Thiourea

Clinical Trials

Ongoing Trials on Thiourea at Clinical Trials.gov

Trial results on Thiourea

Clinical Trials on Thiourea at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Thiourea

NICE Guidance on Thiourea

NHS PRODIGY Guidance

FDA on Thiourea

CDC on Thiourea

Books

Books on Thiourea

News

Thiourea in the news

Be alerted to news on Thiourea

News trends on Thiourea

Commentary

Blogs on Thiourea

Definitions

Definitions of Thiourea

Patient Resources / Community

Patient resources on Thiourea

Discussion groups on Thiourea

Patient Handouts on Thiourea

Directions to Hospitals Treating Thiourea

Risk calculators and risk factors for Thiourea

Healthcare Provider Resources

Symptoms of Thiourea

Causes & Risk Factors for Thiourea

Diagnostic studies for Thiourea

Treatment of Thiourea

Continuing Medical Education (CME)

CME Programs on Thiourea

International

Thiourea en Espanol

Thiourea en Francais

Business

Thiourea in the Marketplace

Patents on Thiourea

Experimental / Informatics

List of terms related to Thiourea


Overview

Thiourea is an organic compound of carbon, nitrogen, sulfur and hydrogen, with the formula CSN2H4 or (NH2)2CS. It is similar to urea, except that the oxygen atom is replaced by a sulfur atom. The properties of urea and thiourea differ significantly because of the relative electronegativities of sulfur and oxygen. Thiourea is a versatile 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.

Structure and bonding

Thiourea is a planar molecule. The C=S bond distance is 1.60±0.1 Å for a wide range of derivatives. This narrow range indicates that the C=S bond is insensitive to the nature of the substitutent. Thus, the thioamide, which is similar to an amide group, is difficult to perturb.

Thiourea occurs in two tautomeric forms:

thiourea

Synthesis of thiourea

The global annual production of thiourea is around 10,000 tons. About 40% is produced in Germany, another 40% in China, and 20% in Japan. Thiourea can be prepared from ammonium thiocyanate but more commonly is synthesized by the reaction of hydrogen sulfide with calcium cyanamide in the presence of carbon dioxide.

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.

Substituted thiourea
Substituted thiourea

Applications of thiourea

Thiourea reduces peroxides to the corresponding diols.[1] The intermediate of the reaction is an unstable epidioxide which can only be identified at -100 ℃. Epidioxide is similar to epoxide except with two oxygen atoms. This intermediate reduces to diol by thiourea.

reduction of cyclic peroxide
reduction of cyclic peroxide

Thiourea is also used in the reductive workup of ozonolysis to give carbonyl compounds.[2] Dimethylsulfide is also an effective reagent for this reaction, but it is highly volatile (b.p. 37 ℃) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity).

reduction cleavage of product from ozonolysis
reduction cleavage of product from ozonolysis

Thiourea is commonly employed to convert alkyl halides to thiols. Such reactions proceed via the intermediacy of isothiuronium salts.[3]. The reaction capitalizes on the high nuceophilicity of the sulfur center and the hydrolytic instability of the isothiuronium salt:

CS(NH2)2 + RX → RSC(NH2)2+X-
RSC(NH2)2+X- + 2 NaOH → RSNa + OC(NH2)2 + NaX
RSNa + HCl → RSH + NaCl

In principle, alkali metal sulfides could also be used to convert alkyl halides to thiols, but thiourea avoids formation of dialkyl sulfides, a side product that plagues the use of Na2S and related reagents.

isothiuronium salt
isothiuronium salt

Thioureas are used a building blocks to pyrimidine derivatives. Thus thioureas condense with β-dicarbonyl compounds.[4] The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine.

pyrimidine derivatives
pyrimidine derivatives

Similarly, aminothiazoles can be synthesized by the reaction of alpha-halo ketones and thiourea.[5]

aminothiazoles
aminothiazoles

Another common application for use of thiourea is a common sulfur source for making semiconductor cadmium sulfide nanoparticle. A slurry of 1 g cadmium sulfate (1.3 mmol), 0.5 g thiourea (6.6 mmol), and 0.1 g SiO2 (1.7 mmol) were sonicated for 3 hours under ambient air at room temperature. The colorless slurry solution changes to yellow indicating the generation of CdS.


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. The liquid silver cleaning product TarnX is essentially a solution of thiourea. A leaching agent for gold leaching and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting.[1]

Safety

A goitrogenic effect (enlargement of the thyroid gland) has been reported, and hepatic tumors have resulted from chronic administration in rat. Bone marrow depression also has been reported.

References

  1. C. Kaneko, A. Sugimoro, and S. Tanaka. A facile one-step synthesis of cis-2-cyclopentene and cis-2-cyclohexene-1,4-diols from the corresponding cyclodienes. “Synthesis”. 876, (1974).
  2. Gupta, D., Soman, G., and Dev, S.. Thiourea, a convenient reagent for the reductive cleavage of olefin ozonolysis products. “Tetrahedron”. 38, 3013 (1982)
  3. Template:OrgSynth
  4. Template:OrgSynth
  5. Dodson, R. M., and King, L. C.. The reaction of ketones with halogens and thiourea. “J. Am. Chem. Soc.”, 67, 2242 (1945).
  6. The Chemistry of double-bonded functional groups edited by S. Patai. pp 1355-1496. John Wiley & Sons. New York, NY, 1977. ISBN 0-471-92493-8.

External links


Template:WH Template:WikiDoc Sources

de:Thioharnstoff