Thursday, 16 July 2009

Monographs: Pharmaceutical substances: Benzocainum - Benzocaine

Molecular formula. C9H11NO2

Relative molecular mass. 165.2

Graphic formula.

Chemical name. Ethyl p-aminobenzoate; ethyl 4-aminobenzoate; CAS Reg. No. 94-09.7.

Other name. Ethyl aminobenzoate.

Description. Colourless crystals or a white, crystalline powder; odourless.

Solubility. Very slightly soluble in water; soluble in 6 parts of ethanol (~750 g/l) TS and 5.5 parts of ether R.

Category. Local anaesthetic.

Storage. Benzocaine should be kept in a well-closed container, protected from light.

Additional information. Benzocaine causes local numbness after being placed on the tongue.


Definition. Benzocaine contains not less than 98.0% and not more than 101.0% of C9H11NO2, calculated with reference to the dried substance.

Identity tests

A. Dissolve 0.10 g in 5 ml of water, add 3 drops of hydrochloric acid (~70 g/l) TS and 5 drops of iodine TS; a brown precipitate is produced.

B. Heat 0.05 g with 2 drops of acetic acid (~300 g/l) TS and 4 drops of sulfuric acid (~1760 g/l) TS; ethyl acetate, perceptible by its odour (proceed with caution), is produced.

C. About 0.05 g yields the reaction described for the identification of primary aromatic amines under 2.1 General identification tests, producing an orange-red precipitate.

Melting range. 88-92°C.

Heavy metals. Use 1.0 g and ethanol (~750 g/l) TS for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 2; determine the heavy metals content according to Method A; not more than 10 μg/g.

Solution in ethanol. A solution of 1.0 g in 10 ml of ethanol (~750 g/l) TS is clear and colourless.

Sulfated ash. Not more than 1.0 mg/g.

Loss on drying. Dry to constant weight at ambient temperature under reduced pressure (not exceeding 0.6 kPa or about 5 mm of mercury) over silica gel, desiccant, R or phosphorus pentoxide R; it loses not more than 10 mg/g.

Acidity or alkalinity. To a solution of 0.5 g in 10 ml of neutralized ethanol TS add 10 ml of carbon-dioxide-free water R and 2 drops of phenolphthalein/ethanol TS; no pink colour is produced. Add 0.5 ml of carbonate-free sodium hydroxide (0.01 mol/l) VS; a pink colour is produced.

Assay. Carry out the assay as described under 2.7 Nitrite titration, using about 0.3 g, accurately weighed, dissolved in 50 ml of hydrochloric acid (~70 g/l) TS and titrate with sodium nitrite (0.1 mol/l) VS. Each ml of sodium nitrite (0.1 mol/l) VS is equivalent to 16.52 mg of C9H11NO2.

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