Benzoic acid is also called benzoic acid. Its molecular formula is C6H5COOH. It is the simplest aromatic acid in which the carboxyl group is directly connected to the carbon atom of the benzene ring. It is a compound formed by replacing a hydrogen on the benzene ring with a carboxyl group (-COOH). It is a colorless, odorless flaky crystal. The melting point is 122.13℃, the boiling point is 249℃, and the relative density is 1.2659 (15/4℃). It sublimates rapidly at 100℃. Its vapor is highly irritating and can easily cause coughing after inhalation. It is slightly soluble in water and easily soluble in organic solvents such as ethanol, ether, chloroform, benzene, toluene, carbon disulfide, carbon tetrachloride and pine oil. It is widely present in nature in the form of free acid, ester or its derivatives. For example, it exists in the form of free acid and benzyl ester in benzoin gum; it exists in the free form in the leaves and stems of some plants; it exists in the form of methyl ester or benzyl ester in essential oils; it exists in the form of its derivative hippuric acid in horse urine. Benzoic acid is a weak acid, stronger than fatty acids. They have similar chemical properties and can form salts, esters, acyl halides, amides, anhydrides, etc., and are not easily oxidized. Electrophilic substitution reactions can occur on the benzene ring of benzoic acid, mainly obtaining meta-substituted products.