Hydroquinone

Hydroquinone
Names
	Preferred IUPAC name Benzene-1,4-diol
	Other names Hydroquinone; Idrochinone; Quinol; 4-Hydroxyphenol; 1,4-Dihydroxybenzene; p-Dihydroxybenzene; p-Benzenediol
Identifiers
CAS Number	123-31-9 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	605970
ChEBI	CHEBI:17594 ;
ChEMBL	ChEMBL537 ;
ChemSpider	764 ;
DrugBank	DB09526;
ECHA InfoCard	100.004.199
EC Number	204-617-8;
Gmelin Reference	2742
KEGG	D00073 ;
PubChem CID	785;
RTECS number	MX3500000;
UNII	XV74C1N1AE ;
UN number	3077, 2662
CompTox Dashboard (EPA)	DTXSID7020716 ;
	InChI InChI=1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H Key: QIGBRXMKCJKVMJ-UHFFFAOYSA-N ; InChI=1/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H Key: QIGBRXMKCJKVMJ-UHFFFAOYAX;
	SMILES c1cc(ccc1O)O;
Properties
Chemical formula	C6H6O2
Molar mass	110.112 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)
Vapor pressure	10−5 mmHg (20 °C)
Acidity (pKa)	9.9
Magnetic susceptibility (χ)	−64.63×10−6 cm3/mol
Structure
Dipole moment	1.4±0.1 D
Pharmacology
ATC code	D11AX11 (WHO)
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H317, H318, H341, H351, H400
Precautionary statements	P201, P202, P261, P264, P270, P272, P273, P280, P281, P301+P312, P302+P352, P305+P351+P338, P308+P313, P310, P321, P330, P333+P313, P363, P391, P405, P501
NFPA 704 (fire diamond)	2 1
Flash point	165 °C (329 °F; 438 K)
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	490 mg/kg (mammal, oral); 245 mg/kg (mouse, oral); 200 mg/kg (rabbit, oral); 320 mg/kg (rat, oral); 550 mg/kg (guinea pig, oral); 200 mg/kg (dog, oral); 70 mg/kg (cat, oral)
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 2 mg/m3
REL (Recommended)	C 2 mg/m3 [15-minute]
IDLH (Immediate danger)	50 mg/m3
Related compounds
Related benzenediols	Pyrocatechol; Resorcinol
Related compounds	1,4-benzoquinone
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C₆H₄(OH)₂. It has 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. The name "hydroquinone" was coined by Friedrich Wöhler in 1843.^[7]

In 2023, it was the 274th most commonly prescribed medication in the United States, with more than 800,000 prescriptions.^[8]^[9]

^ ^a ^b "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 691. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
^ ^a ^b ^c ^d NIOSH Pocket Guide to Chemical Hazards. "#0338". National Institute for Occupational Safety and Health (NIOSH).
^ "Hydroquinone" (PDF). OECD SIDS. UNEP Publications. Archived from the original (PDF) on 20 October 2016. Retrieved 17 September 2018.
^ Lander JJ, Svirbely John J. Lander, W. J. (1945). "The Dipole Moments of Catechol, Resorcinol and Hydroquinone". Journal of the American Chemical Society. 67 (2): 322–324. Bibcode:1945JAChS..67..322L. doi:10.1021/ja01218a051.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ "Hydroquinone". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ "Archived copy" (PDF). Archived (PDF) from the original on 2 February 2014. Retrieved 25 January 2014.{{cite web}}: CS1 maint: archived copy as title (link)
^ F. Wöhler (1844) "Untersuchungen über das Chinon" (Investigations of quinone), Annalen der Chemie und Pharmacie, 51 : 145-163. From page 146: "Das so erhaltene Destillat … enthält … einen neuen, krystallisierenden Körper, den ich unter dem Namen farbloses Hydrochinon weiter unten näher beschreiben werde." (The distillate so obtained … contains … a new, crystallizable substance, that I will describe, under the name of colorless hydroquinone, further below in more detail.) [Note: Wöhler's empirical formula for hydroquinone (p. 152) is incorrect because (1) he attributed 25 (instead of 24) carbon atoms to the molecule, and (2) as many chemists at the time did, he used the wrong atomic masses for carbon (6 instead of 12) and oxygen (8 instead of 16). With these corrections, his empirical formula becomes: C₁₂H₁₂O₄. Dividing the subscripts by 2, the result is: C₆H₆O₂, which is correct.]
^ "The Top 300 of 2023". ClinCalc. Archived from the original on 17 August 2025. Retrieved 17 August 2025.
^ "Hydroquinone Drug Usage Statistics, United States, 2014 - 2023". ClinCalc. Retrieved 17 August 2025.

[iupac2013-1] "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 691. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.

[PGCH-2] NIOSH Pocket Guide to Chemical Hazards. "#0338". National Institute for Occupational Safety and Health (NIOSH).

[3] "Hydroquinone" (PDF). OECD SIDS. UNEP Publications. Archived from the original (PDF) on 20 October 2016. Retrieved 17 September 2018.

[4] Lander JJ, Svirbely John J. Lander, W. J. (1945). "The Dipole Moments of Catechol, Resorcinol and Hydroquinone". Journal of the American Chemical Society. 67 (2): 322–324. Bibcode:1945JAChS..67..322L. doi:10.1021/ja01218a051.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[5] "Hydroquinone". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).

[6] "Archived copy" (PDF). Archived (PDF) from the original on 2 February 2014. Retrieved 25 January 2014.{{cite web}}: CS1 maint: archived copy as title (link)

[7] F. Wöhler (1844) "Untersuchungen über das Chinon" (Investigations of quinone), Annalen der Chemie und Pharmacie, 51 : 145-163. From page 146: "Das so erhaltene Destillat … enthält … einen neuen, krystallisierenden Körper, den ich unter dem Namen farbloses Hydrochinon weiter unten näher beschreiben werde." (The distillate so obtained … contains … a new, crystallizable substance, that I will describe, under the name of colorless hydroquinone, further below in more detail.) [Note: Wöhler's empirical formula for hydroquinone (p. 152) is incorrect because (1) he attributed 25 (instead of 24) carbon atoms to the molecule, and (2) as many chemists at the time did, he used the wrong atomic masses for carbon (6 instead of 12) and oxygen (8 instead of 16). With these corrections, his empirical formula becomes: C₁₂H₁₂O₄. Dividing the subscripts by 2, the result is: C₆H₆O₂, which is correct.]

[8] "The Top 300 of 2023". ClinCalc. Archived from the original on 17 August 2025. Retrieved 17 August 2025.

[9] "Hydroquinone Drug Usage Statistics, United States, 2014 - 2023". ClinCalc. Retrieved 17 August 2025.

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