Pyrithione

Pyrithione

Interconversion of pyrithione tautomers thione form on the left, thiol form on the right
Names
Preferred IUPAC name 1-Hydroxy-2(1H)-pyridinethione (thione) 2-Pyridinethiol 1-oxide (thiol)
Other names Omadine thione: 1-Hydroxypyridine-2-thione       N-Hydroxypyridine-2-thione thiol: 2-Mercaptopyridine monoxide         2-Mercaptopyridine N-oxide         2-Mercaptopyridine 1-oxide
Identifiers
CAS Number	1121-30-8 thione 1121-31-9 thiol 3811-73-2 thiolate salt: sodium 2-pyridinethiolate 1-oxide 15922-78-8 thione salt: sodium 2-thioxo-1(2H)-pyridinolate
3D model (Jmol)	thione: Interactive image thiol: Interactive image thiolate salt: Interactive image thione salt: Interactive image
ChEBI	CHEBI:36578 N
ChemSpider	1514 thione 10446934 thiol 1513 thiolate salt 18517 thione salt
PubChem CID	1570 pyrithione 23685289 sodium pyrithione salt
InChI thione: InChI=1S/C5H5NOS/c7-6-4-2-1-3-5(6)8/h1-4,7H Key: YBBJKCMMCRQZMA-UHFFFAOYSA-N thiol: InChI=1S/C5H5NOS/c7-6-4-2-1-3-5(6)8/h1-4,8H Key: FGVVTMRZYROCTH-UHFFFAOYSA-N thiolate salt: InChI=1S/C5H5NOS.Na/c7-6-4-2-1-3-5(6)8;/h1-4,8H;/q;+1/p-1 Key: WNGMMIYXPIAYOB-UHFFFAOYSA-M thione salt: InChI=1S/C5H4NOS.Na/c7-6-4-2-1-3-5(6)8;/h1-4H;/q-1;+1 Key: XNRNJIIJLOFJEK-UHFFFAOYSA-N
SMILES thione: c1ccn(c(=S)c1)O thiol: C1=CC=[N+](C(=C1)S)[O-] thiolate salt: c1cc[n+](c(c1)[S-])[O-].[Na+] thione salt: c1ccn(c(=S)c1)[O-].[Na+]
Properties
Chemical formula	C5H5NOS
Molar mass	127.16 g·mol−1
Appearance	beige crystalline powder
Melting point	70 to 73 °C (158 to 163 °F; 343 to 346 K)
Solubility in water	2.5 g L−1 at 20 °C
Solubility	Soluble: benzene, chloroform, dichloromethane, dimethylformamide, dimethylsulfoxide, ethyl acetate Slightly soluble: diethyl ether, ethanol, methyl tert-butyl ether, tetrahydrofuran
Acidity (pKa)	−1.95, 4.6
Hazards
R-phrases	R20/21/22, R36/37/38, R63
S-phrases	S22, S24/25, S26, S36/37
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Pyrithione is the common name of an organosulfur compound with molecular formula C
5H
5NOS, chosen as an abbreviation of pyridinethione, and found in the Persian shallot. It exists as a pair of tautomers, the major form being the thione 1-hydroxy-2(1H)-pyridinethione and the minor form being the thiol 2-mercaptopyridine N-oxide; it crystallises in the thione form. It is usually prepared from either 2-bromopyridine,2-chloropyridine, or 2-chloropyridine N-oxide, and is commercially available as both the neutral compound and its sodium salt. It is used to prepare zinc pyrithione, which is used primarily to treat dandruff and seborrhoeic dermatitis in medicated shampoos, though is also an anti-fouling agent in paints.

The preparation of pyrithione was first reported in 1950 by Shaw and was prepared by reaction of 2-chloropyridine N-oxide with sodium hydrogensulfide followed by acidification, or more recently with sodium sulfide. 2-chloropyridine N-oxide itself can be prepared from 2-chloropyridine using peracetic acid. Another approach involves treating the same starting N-oxide with thiourea to afford pyridyl-2-isothiouronium chloride N-oxide which undergoes base hydrolysis to pyrithione.2-Bromopyridine can be oxidised to its N-oxide using a suitable peracid (like 2-chloropyridine), both approaches being analogous to that reported in Organic Syntheses for the oxidation of pyridine to its N-oxide. A substitution reaction using either sodium dithionite (Na
2S
2O
4) or sodium sulfide with sodium hydroxide will allow the replacement of the bromo substituent with a thiol functional group.