4-Hydroxybenzoic acid, also known as
p-hydroxybenzoic acid (
PHBA), is a
monohydroxybenzoic acid, a phenolic derivative of benzoic acid. It is a white crystalline solid that is slightly soluble in water and
chloroform but more soluble in 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 and some ophthalmic solutions. It is
isomeric with 2-hydroxybenzoic acid, known as
salicylic acid, a precursor to
aspirin.