Title: Hydroquinone
CAS Registry Number: 123-31-9
CAS Name: 1,4-Benzenediol
Additional Names: p-dihydroxybenzene; hydroquinol; quinol
Trademarks: Aida (Paraphar); Black and White Bleaching Cream (Plough); Eldoquin (Valeant); Eldopaque (Valeant); Tecquinol
Molecular Formula: C6H6O2
Molecular Weight: 110.11
Percent Composition: C 65.45%, H 5.49%, O 29.06%
Literature References: Prepd by the oxidation of aniline: L. Gattermann, T. Wieland, Die Praxis des Organischen Chemikers (de Gruyter, Berlin, 40th ed., 1961) p 266; by reduction of quinone: Kitchen, US 1322580 (1920); Seyewetz, Miodon, Bull. Soc. Chim. Fr. 33, 449 (1923); by Elbs persulfate oxidation of phenol: Baker, Brown, J. Chem. Soc. 1948, 2303; Forrest, Petrow, ibid. 1950, 2340; from acetylene + CO: Howk, Sauer, US 3055949 (1962 to du Pont). Toxicity data: Woodard et al., Fed. Proc. 8, 348 (1949). Toxicology and carcinogenicity study: F. W. Kari et al., Food Chem. Toxicol. 30, 737 (1992). Review: J. Varagnat in Kirk-Othmer Encyclopedia of Chemical Technology vol. 13 (Wiley-Interscience, New York, 3rd ed., 1981) pp 39-69.
Properties: Crystals, mp 170-171°. d15 1.332. bp 285-287°. Sol in 14 parts water; freely sol in alcohol, ether, slightly in benzene. Its soln becomes brown in the air due to oxidation; the oxidation is very rapid in presence of alkali. Keep well closed and protected from light. Handle with caution. Avoid contact with skin and eyes. LD50 orally in rats: 320 mg/kg (Woodard).
Melting point: mp 170-171°
Boiling point: bp 285-287°
Density: d15 1.332
Toxicity data: LD50 orally in rats: 320 mg/kg (Woodard)
CAUTION: Harmful effects may occur following overexposure to dust and vapors by inhalation or by contact with skin or eyes. Contact with skin may cause dermatitis. Contact with eyes may cause eye irritation, keratitis, discoloration of conjunctiva and corneal changes. Ingestion may cause tinnitus, nausea, dizziness, sense of suffocation, increased respiration rate, vomiting, pallor, muscle twitching, headache, dyspnea, cyanosis, delirium, and collapse. Urine is usually green or brownish green in color and continues to darken on standing. See Patty's Industrial Hygiene and Toxicology vol. 2B, G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, New York, 4th ed., 1994) pp 1590-1592. See also NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 170.
Use: As photographic reducer and developer; as reagent in the determination of small quantities of phosphate; as antioxidant.
Therap-Cat: Depigmentor.
Keywords: Depigmentor.
Hydroxocobalamin Hydroxyamphetamine Hydroxychloroquine Hydroxycodeinone Hydroxydione Sodium

CAS number 123-31-9 YesY
ChemSpider 764 YesY
KEGG D00073 YesY
ChEBI CHEBI:17594 YesY
RTECS number MX3500000
ATC code D11AX11
Jmol-3D images Image 1
Molecular formula C6H6O2
Molar mass 110.11 g mol−1
Appearance white solid
Density 1.3 g cm−3, solid
Melting point 172 °C; 342 °F; 445 K
Boiling point 287 °C; 549 °F; 560 K
Solubility in water 5.9 g/100 mL (15 °C)
Dipole moment 1.4 D
EU classification Harmful (Xn)
Carc. Cat. 3
Muta. Cat. 3
Dangerous for
the environment (N)
R-phrases R22 R40 R41 R43 R50 R68
S-phrases (S2) S26 S36/37/39 S61
NFPA 704
NFPA 704.svg
Flash point 165 °C; 329 °F; 438 K
Related compounds
Related benzenediols Pyrocatechol
Related compounds 1,4-benzoquinone
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, having the chemical formula C6H4(OH)2. Its chemical structure, shown in the table at right, features two hydroxyl groups bonded to a benzene ring in a para position. It is a white granular solid. Substituted derivatives of this parent compound are also referred to as hydroquinones.