Thiocarbonic acid

Thiocarbonic acid is an inorganic acid which is an analog of carbonic acid H2CO3 (or O=C(OH)2), in which all oxygen atoms are replaced with sulfur atoms. It is an unstable hydrophobic red oily liquid with the chemical formula H2CS3 (or S=C(SH)2).[1]

Trithiocarbonic acid
Names
IUPAC name
Carbonotrithioic acid
Systematic IUPAC name
Trithiocarbonic acid
Other names
Thiocarbonic acid
Sulfocarbonic acid
Trisulfocarbonic acid
Dithiocarbon sulfide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.008.931
EC Number
  • 209-822-6
MeSH C013321
UNII
  • InChI=1S/CH2S3/c2-1(3)4/h(H2,2,3,4) ☒N
    Key: HIZCIEIDIFGZSS-UHFFFAOYSA-N ☒N
  • C(=S)(S)S
Properties
CH2S3
Molar mass 110.22 g/mol
Appearance Red oil, yellow solid
Density 1.483 g/cm3(liquid)
Melting point −26.8 °C; −16.3 °F; 246.3 K
Boiling point 58 °C; 136 °F; 331 K
Related compounds
Related compounds
 Carbonic acid, Thiosulfuric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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).

Discovery and synthesis

It was first reported in brief by Zeise in 1824 and later in more detail by Berzelius in 1826,[2] in both cases it was produced by the action of carbon disulfide on a hydrosulfide salt (e.g. potassium hydrosulfide).[3]

CS2 + 2 KSH → K2CS3 + H2S

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 central carbon atom. The C-S bond lengths range from 1.69 to 1.77 Å.[4]

Reactions

Thiocarbonic acid is acidic, with the first pKa being -2.3. The second pKa is near 7. It dissolves S8, but does not react with it.[1]

It reacts with bifunctional reagents to give rings. 1,2-Dichloroethane gives ethylene trithiocarbonate (SCS2C2H4). Oxalyl chloride gives oxalotrithiocarbonate (SCS2(CO)2).

Applications

Thiocarbonic acid currently has no significant applications. Its esters, which are sometimes called thioxanthates, find use in RAFT polymerization.

References
  1. Gattow, Gerhard; Behrendt, Werner (1977). Carbon Sulfides and their Inorganic and Complex Chemistry. Stuttgart: Georg Thieme. p. 154-6. ISBN 3135262014.
  2. Berzelius, J. J. (1826). "Ueber die Schwefelsalze" [About the sulfur salts]. Annalen der Physik (in German). 82 (4): 425–458. Bibcode:1826AnP....82..425B. doi:10.1002/andp.18260820404.
  3. O'Donoghue, Ida Guinevere; Kahan, Zelda (1906). "CLXXIV.—Thiocarbonic acid and some of its salts". J. Chem. Soc., Trans. 89: 1812–1818. doi:10.1039/CT9068901812.
  4. 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.
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