Benzoic acid (/bɛnˈzoʊ.ɪk/) is a white (or colorless) solidorganic compound with the formulaC6H5COOH, whosestructure consists of abenzene ring (C6H6) with acarboxyl (−C(=O)OH)substituent. Thebenzoyl group is often abbreviated "Bz" (not to be confused with "Bn," which is used forbenzyl), thus benzoic acid is also denoted as BzOH, since the benzoyl group has the formula –C6H5CO. It is the simplestaromatic carboxylic acid. The name is derived fromgum benzoin, which was for a long time its only source.
Benzoic acid occurs naturally in many plants[9] and serves as an intermediate in the biosynthesis of manysecondary metabolites.Salts of benzoic acid are used asfood preservatives. Benzoic acid is an importantprecursor for the industrial synthesis of many other organic substances. The salts andesters of benzoic acid are known asbenzoates (/ˈbɛnzoʊ.eɪt/).
The first industrial process involved the reaction ofbenzotrichloride (trichloromethyl benzene) withcalcium hydroxide in water, usingiron or iron salts ascatalyst. The resultingcalcium benzoate is converted to benzoic acid withhydrochloric acid. The product contains significant amounts ofchlorinated benzoic acid derivatives. For this reason, benzoic acid for human consumption was obtained by dry distillation ofgum benzoin. Food-grade benzoic acid is now produced synthetically.
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 byrecrystallization 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. This process usually gives a yield of around 65%.[14]
The temperature required can be lowered to 200 °C by the addition of catalytic amounts of copper(II) salts. The phenol can be converted tocyclohexanol, which is a starting material fornylon synthesis.
Typicalconcentrations of benzoic acid as a preservative in food are between 0.05 and 0.1%. Foods in which benzoic acid may be used and maximum levels for its application are controlled by local food laws.[25][26]
Concern has been expressed that benzoic acid and its salts may react withascorbic acid (vitamin C) in some soft drinks, forming small quantities of carcinogenicbenzene.[27]
Benzoic acid occurs naturally as do its esters in many plant and animal species. Appreciable amounts are found in most berries (around 0.05%). Ripe fruits of severalVaccinium species (e.g.,cranberry,V. vitis macrocarpon;bilberry,V. myrtillus) contain as much as 0.03–0.13% free benzoic acid. Benzoic acid is also formed inapples after infection with the fungusNectria galligena. Among animals, benzoic acid has been identified primarily in omnivorous or phytophageous species, e.g., in viscera and muscles of therock ptarmigan (Lagopus muta) as well as in gland secretions of malemuskoxen (Ovibos moschatus) or Asian bull elephants (Elephas maximus).[32]Gum benzoin contains up to 20% of benzoic acid and 40% benzoic acid esters.[33]
For humans, theWorld Health Organization'sInternational Programme on Chemical Safety (IPCS) suggests a provisional tolerable intake would be 5 mg/kg body weight per day.[32]Cats have a significantly lower tolerance against benzoic acid and itssalts thanrats andmice. Lethal dose for cats can be as low as 300 mg/kg body weight.[41] The oralLD50 for rats is 3040 mg/kg, for mice it is 1940–2263 mg/kg.[32]
InTaipei, Taiwan, a city health survey in 2010 found that 30% of dried and pickled food products had benzoic acid.[42]
^abcBenzoic acid in Linstrom, Peter J.; Mallard, William G. (eds.);NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD) (retrieved 2014-05-23)
^Harris, Daniel (2010).Quantitative Chemical Analysis (8 ed.). New York: W. H. Freeman and Company. pp. AP12.ISBN9781429254366.
^Olmstead, William N.; Bordwell, Frederick G. (1980). "Ion-pair association constants in dimethyl sulfoxide".The Journal of Organic Chemistry.45 (16):3299–3305.doi:10.1021/jo01304a033.
^Santonastaso, Marco; Freakley, Simon J.; Miedziak, Peter J.; Brett, Gemma L.; Edwards, Jennifer K.; Hutchings, Graham J. (21 November 2014). "Oxidation of Benzyl Alcohol using in Situ Generated Hydrogen Peroxide".Organic Process Research & Development.18 (11):1455–1460.doi:10.1021/op500195e.ISSN1083-6160.
^Bedford PG, Clarke EG (1972). "Experimental benzoic acid poisoning in the cat".Vet Rec.90 (3):53–58.doi:10.1136/vr.90.3.53 (inactive 1 November 2024).PMID4672555.S2CID2553612.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
