C6H5CO2H

C6H5CO2H, known as benzoic acid, is the simplest aromatic carboxylic acid. It consists of a carboxyl group attached to a phenyl group (benzenecarboxylic acid). The formula is C7H6O2; often written as C6H5CO2H. It is a colorless crystalline solid that is sparingly soluble in water (approximately 0.29 g/100 mL at 25°C) but dissolves in organic solvents. It melts at 122.4°C and decomposes before boiling. Its pKa (acid dissociation in water) is about 4.2, indicating moderate acidity. It forms water-soluble salts with bases such as NaOH (sodium benzoate).

Industrial production of benzoic acid is mainly by catalytic air oxidation of toluene: C6H5CH3 + 2 O2 → C6H5CO2H + H2O. It can also be produced by oxidation of benzaldehyde or oxidation of cumene derivatives; nonetheless toluene oxidation is dominant. Benzoic acid is a versatile chemical precursor; it can be converted to benzoyl chloride, benzoyl peroxide, and benzoate esters, which serve in perfumes, dyes, pharmaceuticals, and polymerization initiators.

In the food industry, benzoic acid and its salt sodium benzoate are used as preservatives, particularly in acidic foods and beverages (often in very low concentrations). It also occurs in trace amounts in some plants and is a metabolic intermediate in living organisms.

Safety: benzoic acid is an irritant and should be handled with gloves and eye protection. It can be harmful if ingested in large amounts. It may cause adverse reactions in sensitive individuals.