Thiocarboxylic acid

Thiocarboxylic acids are organosulfur compounds with the general formula RC(O)SH. They are related to carboxylic acids by replacement of one oxygen centre by sulfur. Two tautomers are possible, written as RC(S)OH and RC(O)SH, but only the latter is observed.^[1] In the laboratory, the most common thiocarboxylic acid is thioacetic acid. A naturally occurring thiocarboxylic acid is 2,6-pyridinedicarbothioic acid, which functions as a siderophore. Thiocarboxylic acids are more acidic than the corresponding carboxylic acids.

Thiocarboxylic acids are typically prepared from the acid chloride:^[2]

C₆H₅C(O)Cl + KSH → C₆H₅C(O)SH + KCl

Dithiocarboxylic acids

Dithiocarboxylic acids, with the formula RCS₂H, are also known. They are less common than the monothio derivatives. Such compounds are commonly prepared by the reaction of carbon disulfide with a Grignard reagent:^[3]

RMgX + CS₂ → RCS₂MgX

RCS₂MgX + HCl → RCS₂H + MgXCl

References

1. ^ R. J. Cremlyn “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0 471 95512 4.
2. ^ Paul Noble, Jr., D. S. Tarbell (1963), "Thiobenzoic Acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv4p0924 ; Coll. Vol. 4: 924 
3. ^ S. R. Ramadas, P. S. Srinivasan, J. Ramachandran, V. V. S. K. Sastry "Methods of Synthesis of Dithiocarboxylic Acids and Esters" Synthesis 1983; 1983(8): 605-622. doi:10.1055/s-1983-30446