Benzoic acid, C7H6O2 (or C6H5COOH), is a colorless crystalline solid and a simple aromatic carboxylic acid. The name is derived from gum benzoin, which was for a long period of time the only source for benzoic acid. Its salts are used as food preservatives and benzoic acid is an important precursor for the synthesis of many other organic substances.
Benzoic acid is produced commercially by partial oxidation of toluene with oxygen. The process is catalyzed by cobalt or manganese naphthenates. The process uses cheap raw materials, and proceeds in high yield. It can be synthesized through various methods: in laboratory, by hydrolysis, from benzaldehyde, from bromobenzene, from benzyl chloride, and from benzyl alcohol.
Benzoic acid is cheap and readily available, so the laboratory synthesis of benzoic acid is mainly practiced for its pedagogical value. It is a common undergraduate preparation. Benzoic acid can be purified by recrystallization from water because of its high solubility in hot water and poor solubility in cold water. The avoidance of organic solvents for the recrystallization makes this experiment particularly safe.
Like other nitriles and amides, benzonitrile and benzamide can be hydrolyzed to benzoic acid or its conjugate base in acid or basic conditions.
The base-induced disproportionation of benzaldehyde, the Cannizzaro reaction, affords equal amounts of benzoate and benzyl alcohol; the latter can be removed by distillation.
Bromobenzene can be converted to benzoic acid by "carbonation" of the intermediate phenylmagnesium bromide. This synthesis offers a convenient exercise for students to carry out a Grignard reaction, an important class of carbon–carbon bond forming reaction in organic chemistry.
From benzyl alcohol
Benzyl alcohol is refluxed with potassium permanganate or other oxidizing reagents in water. The mixture is hot filtered to remove manganese dioxide and then allowed to cool to afford benzoic acid.
From benzyl chloride
Benzoic acid can be prepared by oxidation of benzyl chloride in the presence of alkaline KMnO4
Benzoic acid and its salts are used as food preservatives. Benzoic acid inhibits the growth of mold, yeast and some bacteria. It is either added directly or created from reactions with its sodium, potassium, or calcium salt. The efficacy of benzoic acid and benzoate is dependent on the pH of the food. Acidic food and beverage like fruit juice (citric acid), sparkling drinks (carbon dioxide), soft drinks (phosphoric acid), pickles (vinegar) or other acidified food are preserved with benzoic acid and benzoates.
Benzoic acid is used as an anti-microbial and anti-fungal agent to preserve drugs, as an intermediate reactive agent to prepare drugs and is also combined with alcohol and water to be used as a cleaning agent in pharmacies.