/bɛnˈzoʊ.ɪk/, 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 time its only known
occurs naturally in many plants and serves as
an intermediate in the biosynthesis of many secondary metabolites.
Salts of benzoic acid are used as food preservatives and 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
2.1 Industrial preparations
2.2 Laboratory synthesis
2.2.1 By hydrolysis
2.2.2 From benzaldehyde
2.2.3 From bromobenzene
2.2.4 From benzyl alcohol
2.2.5 From benzyl chloride
2.2.6 Historical preparation
3.1 Precursor to plasticizers
3.2 Precursor to sodium benzoate and related preservatives
3.5 Niche and laboratory uses
4 Biology and health effects
5.1 Aromatic ring
5.2 Carboxyl group
7 External links
Benzoic acid was discovered in the sixteenth century. The dry
distillation of gum benzoin was first described by
and then by
Alexius Pedemontanus (1560) and Blaise de Vigenère
Pioneer work in 1830 through a variety of experiences based on
amygdalin, obtained from bitter almonds (the fruit of Prunus dulcis)
Pierre Robiquet and Antoine Boutron-Charlard, two French
chemists, had produced benzaldehyde  but they failed in working
out a proper interpretation of the structure of amygdalin that would
account for it, and thus missed the identification of the benzoyl
radical C7H5O. This last step was achieved some few months later
Justus von Liebig
Justus von Liebig and Friedrich Wöhler, who determined the
composition of benzoic acid. These latter also investigated how
hippuric acid is related to benzoic acid.
In 1875 Salkowski discovered the antifungal abilities of benzoic acid,
which was used for a long time in the preservation of
benzoate-containing cloudberry fruits.
It is also one of the chemical compounds found in castoreum. This
compound is gathered from the castor sacs of the North American
Benzoic acid is produced commercially by partial oxidation of toluene
with oxygen. The process is catalyzed by cobalt or manganese
naphthenates. The process uses abundant materials, and proceeds in
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%  The solubility of benzoic acid in over 40 solvents
with references to original sources can be found as part of the Open
Notebook Science Challenge.
Like other nitriles and amides, benzonitrile and benzamide can be
hydrolyzed to benzoic acid or its conjugate base in acid or basic
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 "carboxylation" 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
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:
C6H5CH2Cl + 2 KOH + 2 [O] → C6H5COOH + KCl + H2O
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
Benzoic acid is mainly consumed in the production of phenol by
oxidative decarboxylation at 300−400 °C:
C6H5CO2H + 1/2 O2 → C6H5OH + CO2
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
Precursor to plasticizers
Benzoate plasticizers, such as the glycol-, diethyleneglycol-, and
triethyleneglycol esters, are obtained by transesterification of
methyl benzoate with the corresponding diol. Alternatively these
species arise by treatment of benzoylchloride with the diol. These
plasticizers are used similarly to those derived from terephthalic
Precursor to sodium benzoate and related preservatives
Benzoic acid and its salts are used as a food preservatives,
represented by the
E-numbers E210, E211, E212, and E213. 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 mechanism starts with the absorption of benzoic
acid into the cell. If the intracellular pH changes to 5 or lower, the
anaerobic fermentation of glucose through phosphofructokinase is
decreased by 95%. The efficacy of benzoic acid and benzoate is thus
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.
Typical levels of use for benzoic acid as a preservative in food are
between 0.05–0.1%. Foods in which benzoic acid may be used and
maximum levels for its application are controlled by international
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 benzene.
Benzene in soft drinks
Benzoic acid is a constituent of
Whitfield's ointment which is used
for the treatment of fungal skin diseases such as tinea, ringworm, and
athlete's foot. As the principal component of gum benzoin,
benzoic acid is also a major ingredient in both tincture of benzoin
and Friar's balsam. Such products have a long history of use as
topical antiseptics and inhalant decongestants.
Benzoic acid was used as an expectorant, analgesic, and antiseptic in
the early 20th century.
Benzoic acid is a precursor to benzoyl chloride, C6H5C(O)Cl by
treatment with thionyl chloride, phosgene or one of the chlorides of
Benzoyl chloride is an important starting material for
several benzoic acid derivates like benzyl benzoate, which is used in
artificial flavours and insect repellents.
Niche and laboratory uses
In teaching laboratories, benzoic acid is a common standard for
calibrating a bomb calorimeter.
Biology and health effects
Benzoic acid is relatively nontoxic. It is excreted as hippuric
Benzoic acid is metabolized by butyrate-CoA ligase into an
intermediate product, benzoyl-CoA, which is then metabolized by
glycine N-acyltransferase into hippuric acid.
Benzoic acid occurs naturally as do its esters in many plant and
animal species. Appreciable amounts have been 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
Gum benzoin contains up to 20% of benzoic acid and 40% benzoic acid
Cryptanaerobacter phenolicus is a bacterium species that produces
benzoate from phenol via 4-hydroxybenzoate
Benzoic acid is present as part of hippuric acid (N-benzoylglycine) in
urine of mammals, especially herbivores (Gr. hippos = horse; ouron =
urine). Humans produce about 0.44 g/L hippuric acid in their urine,
and if the person is exposed to toluene or benzoic acid, it can rise
above that level.
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. 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.
The oral LD50 for rats is 3040 mg/kg, for mice it is
In Taipei, Taiwan, a city health survey in 2010 found that 30% of
dried and pickled food products had benzoic acid.
Reactions of benzoic acid can occur at either the aromatic ring or at
the carboxyl group:
Electrophilic aromatic substitution
Electrophilic aromatic substitution reaction will take place mainly in
3-position due to the electron-withdrawing carboxylic group; i.e.
benzoic acid is meta directing.
The second substitution reaction (on the right) is slower because the
first nitro group is deactivating. Conversely, if an activating
group (electron-donating) was introduced (e.g., alkyl), a second
substitution reaction would occur more readily than the first and the
disubstituted product might accumulate to a significant extent.
All the reactions mentioned for carboxylic acids are also possible for
Benzoic acid esters are the product of the acid catalysed reaction
Benzoic acid amides are more easily available by using activated acid
derivatives (such as benzoyl chloride) or by coupling reagents used in
peptide synthesis like DCC and DMAP.
The more active benzoic anhydride is formed by dehydration using
acetic anhydride or phosphorus pentoxide.
Highly reactive acid derivatives such as acid halides are easily
obtained by mixing with halogenation agents like phosphorus chlorides
or thionyl chloride.
Orthoesters can be obtained by the reaction of alcohols under acidic
water free conditions with benzonitrile.
Reduction to benzaldehyde and benzyl alcohol is possible using
DIBAL-H, LiAlH4 or sodium borohydride.
The copper catalysed decarboxylation of benzoate to benzene may be
effected by heating in quinoline. Also, Hunsdiecker decarboxylation
can be achieved by forming the silver salt and heating. Benzoic acid
can also be decarboxylated by heating with an alkali hydroxide or
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Wikimedia Commons has media related to Benzoic acid.
International Chemical Safety Card 0103
SIDS Initial Assessment Report for Benzoic Acid from the Organisation
for Economic Co-operation and Development (OECD)
Local anesthetics (primarily sodium channel blockers) (N01B)
Esters by acid
ArCO2- (not para-amino or Ph)
Bupivacaine# / Levobupivacaine / Ropivacaine
Lidocaine / prilocaine
Anesthetic / vasoconstrictor
‡Withdrawn from market
§Never to phase III
Ectoparasiticides / arthropod (P03A)
‡Withdrawn from market
§Never to phase III
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