4-Hydroxybenzoic acid

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4-Hydroxybenzoic acid
4-Hydroxybenzoic acid
Chemical name 4-Hydroxybenzoic acid
Other names p-Hydroxybenzoic acid
para-Hydroxybenzoic acid
Chemical formula C7H6O3
Molecular mass 138.12 g/mol
CAS number [99-96-7]
Density 1.46 g/cm³
Melting point 214-217 °C
Disclaimer and references

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 soluble to extremely soluble in alcohols, ether, 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.


4-Hydroxybenzoic acid is produced commercially from potassium phenoxide and carbon dioxide in the Kolbe-Schmitt reaction. It can also be produced in the laboratory by heating potassium salicylate with potassium carbonate to 240 °C, followed by treating with acid.[1]

See also

The closely related 2-hydroxybenzoic acid is known as salicylic acid, a precursor to aspirin.


  1. Organic Syntheses, p-hydroxybenzoic acid, Coll. Vol. 2, p. 341 (1943).

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