Benzoic acid is the 1 aromatic acid organic compounds, is also the most simple aromatic acid, chemical formula for C7H6O2. Originally made from benzoin gum, so called benzoic acid, with a slight smell of benzaldehyde or benzoin. The pKa value is 4.2 at room temperature of about 25°C, which is a weak monobasic acid but is more acidic than fatty acid, has a stable chemical structure, and is not easy to be oxidized. Melting point 122.13 ℃, boiling point 249.2 ℃, relative density (15/4 ℃)1.2659. Appearance is white needle-like or scale-like crystal. Sublimation occurs above 100 ℃. Slightly soluble in cold water, hexane, soluble in hot water, ethanol, ether, chloroform, benzene, carbon disulfide and turpentine.