found in the pollen of Pinus densiflora. Chemistry The Hammett equation describes a linear free-energy relationship relating reaction rates and equilibrium constants for many reactions involving benzoic acid derivatives with meta- and para-substituents. Chemical production 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. Chemical reactions 4-Hydroxybenzoic acid has about one tenth the acidity of benzoic acid, having an acid dissociation constant Ka = at 19 °C. Its acid dissociation follows this equation: ⇌ + Chemical use Vectran is a manufactured fiber, spun from a liquid crystal polymer. Chemically it is an aromatic polyester produced by the polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid. The fiber has been shown to exhibit strong radiation shielding used by Bigelow Aerospace and produced by StemRad. 4,4′-Dihydroxybenzophenone is generally prepared by the rearrangement of p-hydroxyphenylbenzoate. Alternatively, p-hydroxybenzoic acid can be converted to p-acetoxybenzoyl chloride. This acid chloride reacts with phenol to give, after deacetylation, 4,4′-dihydroxybenzophenone. Examples of drugs made from PHBA include nifuroxazide, orthocaine, ormeloxifene and proxymetacaine. Bioactivity and safety 4-Hydroxybenzoic acid is a popular antioxidant in part because of its low toxicity. The is 2200 mg/kg in mice (oral). 4-Hydroxybenzoic acid has estrogenic activity both in vitro and in vivo, and stimulates the growth of human breast cancer cell lines. It is a common metabolite of paraben esters, such as methylparaben. The compound is a relatively weak estrogen, but can produce uterotrophy with sufficient doses to an equivalent extent relative to estradiol, which is unusual for a weakly estrogenic compound and indicates that it may be a full agonist of the estrogen receptor with relatively low binding affinity for the receptor. It is about 0.2% to 1% as potent as an estrogen as estradiol. See also Phenolic content in tea Phenolic content in wine References External links Xenoestrogens Monomers Monohydroxybenzoic acids Phenolic human metabolites Vinylogous carboxylic acids