Thiocarbamate

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).

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

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] Other thiocarbamate herbicides are pebulate, molinate, EPTC, butylate, triallate, vernolate and cycloate.^[7]

See also

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