4-Hydroxybenzoic acid

  • PHBS, 4HBA, p- OHB
  • P-hydroxybenzoic
  • Para- hydroxybenzoic acid
  • P- salicylic acid
  • P- oxy-benzoic acid
  • P-hydroxybenzoic

Colorless and odorless, combustible solid


1.46 g · cm -3

213-215 ° C


  • PKS1 = 4.61
  • PKa2 = 9.3
  • Poorly in water (5 g · l-1 at 20 ° C)
  • Insoluble in ethanol, ether and acetone
  • Poorly soluble in chloroform


  • > 5000 mg · kg -1 ( LD50, rat, oral)
  • 2200 mg · kg -1 ( LD50, mouse, oral)

Template: Infobox chemical / molecular formula search available

4-hydroxybenzoic acid is a chemical compound selected from the group consisting of hydroxybenzoic acids. It is a degradation product, and an intermediate in the metabolism of the quinones in eukaryotes.


4-hydroxybenzoic acid is commercially produced from potassium phenolate and carbon dioxide in a Kolbe-Schmitt reaction.

In the laboratory, the preparation of potassium salicylate by heating with potassium carbonate to 240 ° C, followed by treatment with acid ( hydrochloric acid).


4-hydroxybenzoic acid formed from several materials: in plants from its adduct with coenzyme A, itself a result of 4- coumaroyl -CoA; in bacteria in the oxidation of benzoic acid ( EC ), or in the degradation of chorismic acid ( EC ), 4- methoxybenzoic acid ( EC ), 4- hydroxybenzaldehyde ( EC ) or 4 -chlorobenzoic acid ( EC ). Furthermore, it may be oxidized decarboxylated to phenol or 3,4- dihydroxybenzoic acid. In the biosynthesis of ubiquinone, it is linked to a Polyprenylrest.


The aqueous solution of 4- hydroxybenzoic acid reaction ( pH 3.3 at a measurement temperature of 20 ° C and a concentration of 1 g / l).


4- hydroxybenzoic acid is technically mainly used for the production of its esters, the parabens.

Health hazards

The effects of 4- hydroxybenzoic acid on human health and the environment are tested under REACH in 2014 under substance evaluation of the Czech Republic.