Title: Pyrocatechol
CAS Registry Number: 120-80-9
CAS Name: 1,2-Benzenediol
Additional Names: pyrocatechin; catechol; 1,2-dihydroxybenzene
Molecular Formula: C6H6O2
Molecular Weight: 110.11
Percent Composition: C 65.45%, H 5.49%, O 29.06%
Literature References: Prepd by treating salicylaldehyde with hydrogen peroxide, or from its monomethyl ether (guaiacol) by treatment with hydrobromic acid: Dakin, Org. Synth. coll. vol. I, 149 (2nd ed., 1941). Toxicity data: A. J. Lehman et al., Adv. Food Res. 3, 197 (1951). Carcinogenicity study: M. Hirose et al., Carcinogenesis 14, 525 (1993). Review: J. Varagnat, "Hydroquinone, Resorcinol, and Catechol", in Kirk-Othmer Encyclopedia of Chemical Technology vol. 13 (Wiley-Interscience, New York, 3rd ed., 1981) pp 39-69.
Properties: Monoclinic tablets, prisms from toluene. Discolors in air and light. d 1.344; mp 105°; bp760 245.5°; bp400 221.5°; bp200 197.7°; bp100 176°; bp60 161.7°; bp40 150.6°; bp20 134°; bp10 118.3°; bp5 104°. Sublimes. Volatile with steam. pK (18°) 9.48. Sol in 2.3 parts water, in alcohol, benzene, chloroform, ether; very sol in pyridine, aq alkalies. Its aq solns soon turn brown. LD50 in mice (mg/kg): 260 orally; 190 i.p. (Lehman).
Melting point: mp 105°
Boiling point: bp760 245.5°; bp400 221.5°; bp200 197.7°; bp100 176°; bp60 161.7°; bp40 150.6°; bp20 134°; bp10 118.3°; bp5 104°
pKa: pK (18°) 9.48
Density: d 1.344
Toxicity data: LD50 in mice (mg/kg): 260 orally; 190 i.p. (Lehman)
NOTE: Catechol also refers to catechin, q.v.
CAUTION: Potential symptoms of overexposure are irritation of eyes, skin, respiratory system; lacrimation, eye burns; convulsions, increased blood pressure. Direct contact may cause skin sensitization and dermatitis. Systemic effects similar to phenol, q.v. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 56; Patty's Industrial Hygiene and Toxicology vol. 2B, G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, New York, 4th ed., 1994) pp 1584-1586.
Use: In photography; dyeing fur; as reagent.
Therap-Cat: Antiseptic.
Pyrogallol Pyrolan Pyroligneous Acid Pyromellitic Acid Pyronaridine

Pyrocatechol Ball-and-stick model
CAS number 120-80-9 YesY
PubChem 289
ChemSpider 283 YesY
EC number 204-427-5
KEGG C00090 YesY
RTECS number UX1050000
Jmol-3D images Image 1
Molecular formula C6H6O2
Molar mass 110.1 g/mol
Appearance white to brown feathery crystals
Odor faint, phenolic odor
Density 1.344 g/cm³, solid
Melting point 105 °C; 221 °F; 378 K
Boiling point 245.5 °C; 473.9 °F; 518.6 K (sublimes)
Solubility in water 43 g/100 mL
Solubility very soluble in pyridine
soluble in chloroform, benzene, CCl4, ether, acetate
log P 0.88
Vapor pressure 20 Pa (20 °C)
Acidity (pKa) 9.48
Refractive index (nD) 1.604
Crystal structure monoclinic
MSDS Sigma-Aldrich
EU classification Harmful (Xn)
R-phrases R21/22, R36/38
S-phrases (S2), S22, S26, S37
NFPA 704
NFPA 704.svg
Flash point 127 °C; 261 °F; 400 K
Autoignition temperature 510 °C; 950 °F; 783 K
Related compounds
Related benzenediols Resorcinol
Related compounds 1,2-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

Catechol, also known as pyrocatechol or 1,2-dihydroxybenzene, is an organic compound with the molecular formula C6H4(OH)2. It is the ortho isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amounts. It was first discovered by destructive distillation of the plant extract catechin. About 20 million kg are now synthetically produced annually as a basic organic chemical, mainly as a precursor to pesticides, flavors, and fragrances.

Catechol occurs as feathery white crystals that are very rapidly soluble in water.

(The name "catechol" has also been used as a chemical class name, where it refers generally to the catechins.)