Thiobenzoic acid

Thiobenzoic acid is an organosulfur compound with molecular formula C₆H₅COSH. It is the parent of aryl thiocarboxylic acids. It is a pale yellow liquid that freezes just below room temperature. The structure of thiobenzoic acid has not been examined by X-ray crystallography but the 4-methyl derivative has been reported. The CC(O)SH group is planar with syn geometry. The C=O and C-S lengths are respectively 120 and 177 pm.^[1]

Thiobenzoic acid

Names
Preferred IUPAC name Benzenecarbothioic S-acid
Other names Benzoyl thiol Monothiobenzoic acid
Identifiers
CAS Number	98-91-9 Y
3D model (JSmol)	Interactive image
ChemSpider	7136
ECHA InfoCard	100.002.466
EC Number	202-712-9202-712-9
Gmelin Reference	1071790
PubChem CID	7414
RTECS number	DH6839000
UNII	GBG5RLO56N Y
CompTox Dashboard (EPA)	DTXSID3059181
InChI InChI=1S/C7H6OS/c8-7(9)6-4-2-1-3-5-6/h1-5H,(H,8,9)
SMILES C1=CC=C(C=C1)C(=O)S
Properties
Chemical formula	C7H6OS
Molar mass	138.18 g·mol−1
Appearance	yellow liquid
Density	1.1775 g/cm3
Melting point	24 °C (75 °F; 297 K)
Boiling point	222 °C (432 °F; 495 K)
Solubility in water	soluble
Vapor pressure	0.1
Acidity (pKa)	2.48
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis and reactions

Thiobenzoic acid is prepared by treatment of benzoyl chloride with potassium hydrosulfide:^[2]

C₆H₅C(O)Cl + KSH → C₆H₅C(O)SH + KCl

With a pK_a near 2.5, this acid is almost 100x more acidic than benzoic acid.^[3] The conjugate base is thiobenzoate, C₆H₅COS⁻.

Oxidation of thiobenzoic acid gives the disulfide (C₆H₅C(O)S)₂.^[4]

See also

• Dithiobenzoic acid