Benzoic acid/bɛnˈzoʊ.ɪk/ is a white (or colorless) solid organic compound with the formula C6H5COOH, whose structure consists of a benzene ring (C6H6) with a carboxyl (−C(=O)OH) substituent. The benzoyl group is often abbreviated "Bz" (not to be confused with "Bn" which is used for benzyl), thus benzoic acid is also denoted as BzOH, since the benzoyl group has the formula –C6H5CO. It is the simplest aromatic carboxylic acid. The name is derived from gum 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 many secondary metabolites. Salts of benzoic acid are used as food preservatives. Benzoic acid is an important precursor for the industrial synthesis of many other organic substances. The salts and esters of benzoic acid are known as benzoates/ˈbɛnzoʊ.eɪt/.
In 1875 Salkowski discovered the antifungal properties of benzoic acid, which was used for a long time in the preservation of benzoate-containing cloudberry fruits.[12][disputed – discuss]
The first industrial process involved the reaction of benzotrichloride (trichloromethyl benzene) with calcium hydroxide in water, using iron or iron salts as catalyst. The resulting calcium benzoate is converted to benzoic acid with hydrochloric acid. The product contains significant amounts of chlorinated benzoic acid derivatives. For this reason, benzoic acid for human consumption was obtained by dry distillation of gum 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 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. 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 to cyclohexanol, which is a starting material for nylon synthesis.
Typical concentrations 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 with ascorbic acid (vitamin C) in some soft drinks, forming small quantities of carcinogenic benzene.[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 several Vaccinium 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 in apples after infection with the fungus Nectria galligena. Among animals, benzoic acid has been identified primarily in omnivorous or phytophageous species, e.g., in viscera and muscles of the rock ptarmigan (Lagopus muta) as well as in gland secretions of male muskoxen (Ovibos moschatus) or Asian bull elephants (Elephas maximus).[32]Gum benzoin contains up to 20% of benzoic acid and 40% benzoic acid esters.[33]
In terms of its biosynthesis, benzoate is produced in plants from cinnamic acid.[34] A pathway has been identified from phenol via 4-hydroxybenzoate.[35]
For humans, the World Health Organization's International 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 its salts than rats and mice. Lethal dose for cats can be as low as 300 mg/kg body weight.[41] The oral LD50 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.
^Donald L. Pavia (2004). Introduction to Organic Laboratory Techniques: A Small Scale Approach. Thomson Brooks/Cole. pp. 312–314. ISBN978-0-534-40833-6.
^Shirley, D. A. (1954). "The Synthesis of Ketones from Acid Halides and Organometallic Compounds of Magnesium, Zinc, and Cadmium". Org. React.8: 28–58.
^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.
^Pastrorova I, de Koster CG, Boom JJ (1997). "Analytic Study of Free and Ester Bound Benzoic and Cinnamic Acids of Gum Benzoin Resins by GC-MS HPLC-frit FAB-MS". Phytochem Anal. 8 (2): 63–73. doi:10.1002/(SICI)1099-1565(199703)8:2<63::AID-PCA337>3.0.CO;2-Y.
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