Dithiocarboxylic acid

Dithiocarboxylic acids are organosulfur compounds with the formula . They are the dithia analogues of carboxylic acids. A closely related and better studied family of compounds are the monothiocarboxylic acids, with the formula .

Dithiocarboxylic acids are about 3x more acidic than the monothiocarboxylic acids. Thus, for dithiobenzoic acid pKa = 1.92. Contrariwise, they do not exhibit hydrogen bonding.{{cite book|title=Carboxylic Acids and Esters|chapter=Thiolo, Thiono and Dithio Acids and Esters|author=Matthys J. Janssen|editor=Saul Patai|year=1969|doi=10.1002/9780470771099.ch15

Such compounds are commonly prepared by the reaction of carbon disulfide with a Grignard reagent: : : This reaction is comparable to the formation of carboxylic acids using a Grignard reagent and carbon dioxide.

Nitrogen derivatives substitute onto dithioic acids similar to the monothioic and carboxylic acids. Thus amines ammonolyze to thioamides or amidines, hydrazines to thio-hydrazides, and hydroxylamines to thio-hydroxamic acids or nitriles. Likewise, unsaturated (i.e., allylic, vinylic, propargylic, or acetylenic) Grignard reagents attack dithioesters with an allylic shift much like a traditional Grignard reaction. In other cases, the carbonyl polarity is reversed: thus saturated Grignards alkylate the sulfur atoms to form a dithioacetal carbanion. Ketonic dithioesters react at the dithioester first, before the resulting carbanion attacks the ketone to form a cyclic alcohol.

Aryldithiocarboxylic acids, e.g., dithiobenzoic acid, chlorinate to give the thioacyl chlorides. Oxygen transfer from e.g. air Dithiocarboxylate salts readily S-alkylate to give dithiocarboxylate esters: : Dithioketene acetals (i.e., dithioate enol dithioethers) are nucleophilic at the sulfur atoms, not the α carbon.