Boric Acid

Boric Acid

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Boric Acid

Boric acid occurs as a hygroscopic, white crystalline powder, colorless shiny plates, or white crystals.

Nonproprietary Names

  • BP: Boric Acid
  • JP: Boric Acid
  • PhEur: Boric Acid
  • USP-NF: Boric Acid

Synonyms
Acidum boricum; boracic acid; boraic acid; Borofax; boron trihydroxide; E284; orthoboric acid; trihydroxyborene.

Chemical Name and CAS Registry Number

Orthoboric acid [10043-35-3] Metaboric acid [13460-50-9]



Empirical Formula and Molecular Weight

H3BO3 61.83 (for trihydrate) HBO2 43.82 (for monohydrate)

Functional Category: Antimicrobial preservative; buffering agent.

Applications in Pharmaceutical Formulation or Technology

Boric acid is used as an antimicrobial preservative in eye drops, cosmetic products, ointments, and topical creams. It is also used as an antimicrobial preservative in foods. Boric acid and borate have good buffering capacity and are used to control pH; they have been used for this purpose in external preparations such as eye drops.

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Boric acid has also been used therapeutically in the form of suppositories to treat yeast infections. In dilute concentrations it is used as a mild antiseptic, with weak bacteriostatic and fungistatic properties, although it has generally been superseded by more effective and less toxic disinfectants.

Method of Manufacture

Boric acid occurs naturally as the mineral sassolite. However, the majority of boric acid is produced by reacting inorganic borates with sulfuric acid in an aqueous medium. Sodium borate and partially refined calcium borate (colemanite) are the principal raw materials.

When boric acid is made from colemanite, the fineground ore is vigorously stirred with mother liquor and sulfuric acid at about 908C. The by-product calcium sulfate is removed by filtration, and the boric acid is crystallized by cooling the filtrate.

Related Substances

Sodium borate

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