It is often referred to as trithiocarbonic acid so as to differentiate it from other carbonic acids containing sulfur, such as monothiocarbonic O,O-acid S=C(OH)2, monothiocarbonic O,S-acid O=C(OH)(SH), dithiocarbonic O,S-acid S=C(OH)(SH) and dithiocarbonic S,S-acid O=C(SH)2 (see thiocarbonates).
Treatment with acids liberates the thiocarbonic acid as a red oil:
K2CS3 + 2 HX → H2CS3 + 2 KX
Both the acid and many of its salts are unstable and decompose via the release of carbon disulfide, particularly upon heating:
H2CS3 → CS2 + H2S
An improved synthesis involves addition of barium trithiocarbonate to hydrochloric acid at 0 °C. This method provided samples with which many measurement have been made.[1]
Despite its lability, crystals of thiocarbonic acid have been examined by X-ray crystallography, which confirms the anticipated molecular structure of a trigonal planar molecular geometry at the central carbon atom. The C-S bond lengths range from 1.69 to 1.77 Å.[4]
Reactions and derivatives
Thiocarbonic acid is acidic, with the first pKa being around 2. The second pKa is near 7. It dissolves S8, but does not react with it.[1]
Thiocarbonic acid currently has no significant applications. Its esters find use in RAFT polymerization.
References
^ abcGattow, Gerhard; Behrendt, Werner (1977). Carbon Sulfides and their Inorganic and Complex Chemistry. Stuttgart: Georg Thieme. p. 154-6. ISBN3135262014.
^Krebs, B.; Gattow, G. (1965). "Über Chalkogenocarbonate. XIV. Das Kohlenstoffsulfid-bis-(hydrogensulfid) SC(SH)2 und das System H2S−CS2 6. Die Kristallstruktur der Trithiokohlensure bei -100 ″C". Zeitschrift für anorganische und allgemeine Chemie. 340 (5–6): 294–311. doi:10.1002/zaac.19653400508.