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Benzoic Acid

Acidum benzoicum; benzenecarboxylic acid; benzeneformic acid

Benzoic acid occurs as feathery, light, white or colorless crystals or powder. It is essentially tasteless and odorless or with a slight characteristic odor suggestive of benzoin.

Nonproprietary Names

  • BP: Benzoic Acid
  • JP: Benzoic Acid
  • PhEur: Benzoic Acid
  • USP: Benzoic Acid
Acidum benzoicum; benzenecarboxylic acid; benzeneformic acid; carboxybenzene; dracylic acid; E210; phenylcarboxylic acid; phenylformic acid.

Chemical Name and CAS Registry Number
Benzoic acid [65-85-0]

Empirical Formula and Molecular Weight
C7H6O2 122.12

Functional Category
Antimicrobial preservative; therapeutic agent.

Applications in Pharmaceutical Formulation or Technology

Benzoic acid is widely used in cosmetics, foods, and pharmaceuticals, as an antimicrobial preservative. Greatest activity is seen at pH values between 2.5–4.5. Benzoic acid also has a long history of use as an antifungal agent in topical therapeutic preparations such as Whitfield’s ointment (benzoic acid 6% and salicylic acid 3%).

Method of Manufacture

Although benzoic acid occurs naturally, it is produced commercially by several synthetic methods. One process involves the continuous liquid-phase oxidation of toluene in the presence of a cobalt catalyst at 150–2008C and 0.5–5.0 MPa (5.0–50.0 atm) pressure to give a yield of approximately 90% benzoic acid.

Benzoic acid can also be produced commercially from benzotrichloride or phthalic anhydride. Benzotrichloride, produced by chlorination of toluene, is reacted with 1 mole of benzoic acid to yield 2 moles of benzoyl chloride. The benzoyl chloride is then converted to 2 moles of benzoic acid by hydrolysis. Yield is 75–80%.

In another commercial process, phthalic anhydride is converted to benzoic acid, in about an 85% yield, by hydrolysis in the presence of heat and chromium and disodium phthalates. Crude benzoic acid is purified by sublimation or recrystallization.

Related Substances

Potassium benzoate; sodium benzoate.

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