4hydroxybenzoic

4-hydroxybenzoic acid, also known as p-hydroxybenzoic acid (PHBA), is an organic compound that consists of a benzene ring bearing a para-hydroxyl group and a carboxylic acid group. It is one of several hydroxybenzoic acids and has the molecular formula C7H6O3. It is a white crystalline solid with a high melting point and limited water solubility at room temperature, though the solubility increases in hot water and in many organic solvents.

PHBA occurs in nature in trace amounts in various plants and is also produced synthetically on an industrial scale. Industrial production commonly involves oxidation of suitable precursors or derivatization routes that introduce the hydroxy and carboxyl substituents in the para position. As a versatile chemical building block, it serves as an intermediate for the synthesis of larger molecules.

In commerce, PHBA is best known as the precursor to a family of preservatives known as parabens. Esters of p-hydroxybenzoic acid with alkyl groups (such as methyl, ethyl, propyl, and butyl) are widely used as preservatives in cosmetics, pharmaceuticals, and some foods due to their antimicrobial properties. The acid itself also finds use in the synthesis of dyes, fragrances, and certain polymer products, including specialty polyesters and alkyd resins.

Safety and handling information align with its classification as a chemical irritant. PHBA can irritate the skin, eyes, and respiratory tract upon exposure. It should be handled with appropriate personal protective equipment and standard laboratory or industrial hygiene practices, including avoidance of inhalation and prolonged skin contact.