phydroxybenzoic

P-hydroxybenzoic acid, also known as 4-hydroxybenzoic acid (PHBA), is a monohydroxybenzoic acid with the chemical formula C7H6O3. It features a benzene ring bearing a carboxylic acid group and a para-hydroxyl substituent. The compound occurs in small amounts in some plants and serves as a metabolic intermediate in the biosynthesis of ubiquinone (coenzyme Q) in bacteria and plants.

In industry, p-hydroxybenzoic acid is produced and used as a chemical intermediate on a large scale. It is a starting point for the synthesis of parabens, a family of esters such as methylparaben, ethylparaben, and propylparaben, which are widely employed as preservatives in cosmetics, foods, and pharmaceuticals. The acid can also be utilized in the manufacture of certain dyes, polymers, and specialty chemicals.

Physical and chemical properties include its status as a crystalline solid with a melting point around 214–216 °C and a molecular weight of 138.12 g/mol. It behaves as a weak acid due to its carboxyl group, with a pKa typically in the mid-4 range. Its aqueous solubility is relatively limited at ambient temperatures, increasing with heat.

Safety and handling are generally straightforward for laboratory and industrial contexts. PHBA is of low acute toxicity, but standard precautions for handling organic acids apply, including avoiding inhalation of dust and contact with skin or eyes. Some individuals may exhibit sensitization or allergic responses, and appropriate safety data sheets should be consulted for detailed guidance.