2-Fluoro-4-hydroxybenzoic acid (CAS number 65145-13-3), a para-hydroxybenzoic acid, carries a fluoride group at ortho-position. The para-positioning of carboxylic acid and hydroxy in 2-fluoro-4-hydroxybenzoic acid is preferred for synthesizing mesogens used in liquid crystal. The long alkyl tail readily attaches to the molecule with alkyl bromide under basic condition. The ortho-positioned fluoride group introduces an additional intercalated smectic phase.
In cancer immunotherapy, an immunoadjuvant is synthesized with 2-fluoro-4-hydroxybenzoic acid and polyphosphorzene. The reaction initiates with a ring-opening polymerization of hexachlorocyclotriphosphazene, followed by a nucleophilic substitution of the deprotonated phenoxide from 2-fluoro-4-hydroxybenzoic acid.