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Revision as of 09:15, 29 November 2010
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Names | |||
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IUPAC name
4-Hydroxybenzoic acid
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Other names
p-Hydroxybenzoic acid
para-Hydroxybenzoic acid | |||
Identifiers | |||
3D model (JSmol)
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ChemSpider | |||
ECHA InfoCard | 100.002.550 | ||
PubChem CID
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CompTox Dashboard (EPA)
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Properties | |||
C7H6O3 | |||
Molar mass | 138.12074 g/mol | ||
Density | 1.46 g/cm³ | ||
Melting point | 214-217 °C | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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4-Hydroxybenzoic acid, or p-hydroxybenzoic acid, is a phenolic derivative of benzoic acid. It is a white crystalline solid that is slightly soluble in water and chloroform but more soluble polar organic solvents such as alcohols and acetone. 4-Hydroxybenzoic acid is primarily known as the basis for the preparation of its esters, known as parabens, which are used as preservatives in cosmetics. It is isomeric with 2-hydroxybenzoic acid, known as salicylic acid, a precursor to aspirin.
Production
4-Hydroxybenzoic acid is produced commercially from potassium phenoxide and carbon dioxide in the Kolbe-Schmitt reaction.[1]
4-Hydroxybenzoic acid can also be produced in the laboratory by heating potassium salicylate with potassium carbonate to 240 °C, followed by treating with acid.[2]
Reactions
It is about 10x less acidic than benzoic acid, Ka = 3.3 x 10−5 M at 19 °C:
- HOC6H4CO2H HOC6H4CO2- + H+
Safety
4-Hydroxybenzoic acid is popular antioxidant in part because of its low toxicity. The LD50 is 2200 mg/kg in mice (oral).
References
- ^ Edwin Ritzer and Rudolf Sundermann “Hydroxycarboxylic Acids, Aromatic” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_519
- ^ C. A. Buehler and W. E. Cate (1943). "p-Hydroxybenzoic acid". Organic Syntheses; Collected Volumes, vol. 2, p. 341.