Thiocarbonic acid

Thiocarbonic acid is an acid with the chemical formula H₂CS₃ (or S=C(SH)₂). It 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.^[1]

Trithiocarbonic acid

Names
IUPAC name Carbonotrithioic acid
Systematic IUPAC name Trithiocarbonic acid
Other names Dithiocarbon sulfide Sulfocarbonic acid Thiocarbonic acid Trisulfocarbonic acid
Identifiers
CAS Number	594-08-1 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:36967 N
ChemSpider	62204 N
ECHA InfoCard	100.008.931
EC Number	209-822-6
MeSH	C013321
PubChem CID	68982
UNII	O27JHO40J8 Y
CompTox Dashboard (EPA)	DTXSID00862140
InChI InChI=1S/CH2S3/c2-1(3)4/h(H2,2,3,4) N Key: HIZCIEIDIFGZSS-UHFFFAOYSA-N N
SMILES C(=S)(S)S
Properties
Chemical formula	H2CS3
Molar mass	110.21 g·mol−1
Appearance	Red oily liquid, yellow crystalline 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 Thiocarbonate Xanthic acid Thioxanthate Ethyl xanthic acid Thiocyanic acid Thiocyanate Potassium trithiocarbonate Dimethyl trithiocarbonate Ethylene trithiocarbonate Thiourea Thiocarbamate Thiophosphoric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) 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]

BaCS₃ + 2 HCl → H₂CS₃ + BaCl₂

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 pK_a being around 2. The second pK_a is near 7. It dissolves S₈, but does not react with it.^[1]

Salts and esters of trithiocarbonic acid are called trithiocarbonates, and they are sometimes called thioxanthates.

Thiocarbonic acid reacts with bifunctional reagents to give rings. 1,2-Dichloroethane gives ethylene trithiocarbonate (S=CS₂(CH₂)₂). Oxalyl chloride gives oxalyl trithiocarbonate (S=CS₂(C=O)₂).

Some of the organic trithiocarbonates

• 
  Ethylene trithiocarbonate
• 
  Oxalyl trithiocarbonate
• 
  Dimethyl trithiocarbonate

Applications

Thiocarbonic acid currently has no significant applications. Its esters find use in RAFT polymerization.