Dithiocarboxylic acid

Dithiocarboxylic acids are organosulfur compounds with the formula RCS₂H. They are the dithia analogues of carboxylic acids. A closely related and better studied family of compounds are the monothiocarboxylic acids, with the formula RCOSH. ^[1]

Dithiocarboxylic acids are about 3x more acidic than the monothiocarboxylic acids. Thus, for dithiobenzoic acid pK_a = 1.92. Contrariwise, they do not exhibit hydrogen bonding. ^[2]

Such compounds are commonly prepared by the reaction of carbon disulfide with a Grignard reagent: ^[3]

RMgX + CS₂ → RCS₂MgX

RCS₂MgX + HCl → RCS₂H + MgXCl

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. ^{[2] : 749–750} 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. ^{[4] : 1047}

Aryldithiocarboxylic acids, e.g., dithiobenzoic acid, chlorinate to give the thioacyl chlorides.^{[ citation needed ]} Oxygen transfer from e.g. air ^{[2] : 750} to a dithiocarboxylate ester gives a sulfine-like S-oxide that rearranges to an acyl disulfide. ^[5] Dithiocarboxylate salts readily S-alkylate to give dithiocarboxylate esters: ^[6]

RCS₂Na + R'Cl → RCS₂R' + NaCl

Dithioketene acetals (i.e., dithioate enol dithioethers) are nucleophilic at the sulfur atoms, not the α carbon. ^{[2] : 757}

References

1. Grote, Johanna; Friedrich, Felix; Berthold, Katarína; Hericks, Loreen; Neumann, Beate; Stammler, Hans-Georg; Mitzel, Norbert W. (2018). "Dithiocarboxylic Acids: An Old Theme Revisited and Augmented by New Preparative, Spectroscopic and Structural Facts". Chemistry – A European Journal. 24 (11): 2626–2633. doi:10.1002/chem.201704235. PMID   29266463.
2. Matthys J. Janssen (1969). "Thiolo, Thiono and Dithio Acids and Esters". In Saul Patai (ed.). Carboxylic Acids and Esters. PATAI'S Chemistry of Functional Groups. pp. 705–764. doi:10.1002/9780470771099.ch15. ISBN   978-0-470-77109-9.
3. Ramadas, S. R.; Srinivasan, P. S.; Ramachandran, J.; Sastry, V. V. S. K. (1983). "Methods of Synthesis of Dithiocarboxylic Acids and Esters". Synthesis. 1983 (8): 605–622. doi:10.1055/s-1983-30446. S2CID   96087227.
4. Voss, J. (1979). "The chemistry of thio acid derivatives". In Patai, Saul (ed.). The Chemistry of Acid Derivatives. The Chemistry of Functional Groups, Supplement B. Vol. 1, Part 2. Chichester, WSX: Interscience (Wiley). pp. 1021–1062. ISBN   0 471 99611 4. LCCN   75-6913.
5. Collier, S. J. (2007). "Product class 8: Thiocarboxylic S-acids, selenocarboxylic Se-acids, tellurocarboxylic Te-acids, and derivatives". In Panek, J. S. (ed.). Category 3, Compounds with Four and Three Carbon Heteroatom Bonds: Three Carbon—Heteroatom Bonds: Esters, and Lactones; Peroxy Acids and R(CO)OX Compounds; R(CO)X, X=S, Se, Te. Science of Synthesis. Stuttgart: Georg Thieme Verlag. p. 1651. doi:10.1055/sos-sd-020-01480. ISBN   978-3-13-144691-6.
6. Frederick Kurzer; Alexander Lawson (1962). "Thiobenzoylthioglycolic Acid". Org. Synth. 42: 100. doi: 10.15227/orgsyn.042.0100 .