Thiocarbamate

General structural formulae of O-organyl (1) and S-organyl (2) thiocarbamates

In organic chemistry, thiocarbamates (thiourethanes) are a family of organosulfur compounds. As the prefix thio- suggests, they are sulfur analogues of carbamates. There are two isomeric forms of thiocarbamates: O-thiocarbamates, ROC(=S)NR₂ (esters), and S-thiocarbamates, RSC(=O)NR₂ (thioesters).

Synthesis

Thiocarbamates can be synthesised by the reaction of water or alcohols upon thiocyanates (Riemschneider thiocarbamate synthesis):[1][2]

RSCN + H₂O → RSC(=O)NH₂

RSCN + R'OH → RSC(=O)NR'H

Similar reactions are seen between alcohols and thiocarbamoyl chlorides such as dimethylthiocarbamoyl chloride; as well as between thiols and cyanates.[2] The herbicide Cycloate is produced in this way:

C₆H₁₁(C₂H₅)NCOCl + C₂H₅SH → C₆H₁₁(C₂H₅)NCOSC₂H₅ + HCl

Other related thiocarbamate herbicides include vernolate (C₃H₇)₂NCOSC₃H₇ and triallate ((i−C₃H₇)₂NCOSCH₂CCl=CCl₂.[3]

Salts of thiocarbamate arise by the reaction of amines with carbonyl sulfide:

2 R₂NH + COS → [R₂NH+2][R₂N−COS^−]

Reactions

In the Newman-Kwart rearrangement O-thiocarbamates can isomerise to S-thiocarbamates.[4] This reaction, which generally requires high temperatures, is an important method for the synthesis of thiophenols.

Occurrence

Chemical structure of goitrin

Goitrin is a cyclic thiocarbamate found in some vegetables.[5]

Uses

Thiocarbamate based herbicides (e.g. prosulfocarb) were introduced in 1957 and in 2017 was a $200,000,000 market.[6]

See also

• Dithiocarbamate
• Carbamate
• Tolnaftate, a thiocarbamate used as an antifungal agent

References

1. Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, p. 1269, ISBN 978-0-471-72091-1
2. Walter, W.; Bode, K.-D. (April 1967). "Syntheses of Thiocarbamates". Angewandte Chemie International Edition in English. 6 (4): 281–293. doi:10.1002/anie.196702811.
3. Appleby, Arnold P.; Müller, Franz; Carpy, Serge (2001). "Weed Control". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a28_165. ISBN 3-527-30673-0.
4. Newman, Melvin S.; Hetzel, Frederick W. (1971). "Thiophenols from Phenols: 2-Naphthalenethiol". Org. Synth. 51: 139. doi:10.15227/orgsyn.051.0139.
5. McMillan M, Spinks EA, Fenwick GR (January 1986). "Preliminary Observations on the Effect of Dietary Brussels Sprouts on Thyroid Function". Hum Toxicol. 5 (1): 15–19. doi:10.1177/096032718600500104. PMID 2419242.
6. "Agrochemical industry development, trends in R&D and the impact of regulation". Pest Management Science. 19 Dec 2019. Retrieved 6 August 2024.