Page 142 - Chemical and process design handbook

Speight_Part II_B 11/7/01 3:11 PM Page 2.83

BENZOIC ACID

Benzoic acid (C H COOH, phenyl formic acid, melting point: 121.7°C,
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boiling point: 249.2°C, density: 1.266) is a white crystalline solid that sub-
limes readily at 100°C and is volatile in steam. Benzoic acid is insoluble in
cold water but is readily soluble in hot water or in alcohol or ether.
Although benzoic acid occurs naturally in some substances, such as
gum benzoin, dragon’s blood resin, balsams, cranberries, and the urine of
the ox and horse, the product is made on a large scale by synthesis from
other materials. Benzoic acid can be manufactured by the liquid-phase
oxidation of toluene by air in a continuous oxidation reactor operated at
moderate pressure and temperature:
2C H CH + 3O → 2C H COOH + 4H O
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Benzoic acid also can be obtained as a by-product of the manufacture of
benzaldehyde from benzal chloride or benzyl chloride.
Benzoic acid is used as a starting or intermediate material in various
industrial organic syntheses, especially in the manufacture of terephthalic
acid. Benzoic acid forms benzoates; e.g., sodium benzoate and calcium
benzoate which, when heated with calcium oxide, yields benzene and cal-
cium. With phosphorus trichloride, benzoic acid forms benzoyl chloride
(C H COCl), an agent for the transfer of the benzoyl group (C H CO-).
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Benzoic acid reacts with chlorine to form m-chlorobenzoic acid and reacts
with nitric acid to form m-nitrobenzoic acid. Benzoic acid forms a number
of useful esters such as methyl benzoate, ethyl benzoate, glycol diben-
zoate, and glyceryl tribenzoate.

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