Wednesday, 15 July 2009

Monographs: Pharmaceutical substances: Acidum salicylicum - Salicylic acid

Molecular formula. C7H6O3

Relative molecular mass. 138.1

Graphic formula.

Chemical name. 2-Hydroxybenzoic acid; CAS Reg. No. 69-72-7.

Description. Colourless crystals, usually needle-like, or a white, crystalline powder; odourless.

Solubility. Slightly soluble in water; soluble in 4 parts of ethanol (~750 g/l) TS and in 3 parts of ether R.

Category. Keratolytic.

Storage. Salicylic acid should be kept in a well-closed container.


Definition. Salicylic acid contains not less than 99.0% and not more than 101.0% of C7H6O3, calculated with reference to the dried substance.

Identity test

Dissolve 0.14 g in 1 ml of sodium hydroxide (1 mol/l) VS and add 5 ml of water; this solution yields the reaction described under 2.1 General identification tests as characteristic of salicylates.

Melting range. 158-161°C.

Heavy metals. Use 2.0 g and 15 ml of 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 20 μg/g.

Chlorides. Dissolve 1.7 g in 40 ml of boiling water, cool and filter. Add 2 ml of nitric acid (~130 g/l) TS to the filtrate and proceed as described under 2.2.1 Limit test for chlorides; the chloride content is not more than 0.15 mg/g.

Sulfates. Dissolve 2.5 g in 40 ml of boiling water, cool, filter, and proceed with the filtrate as described under 2.2.2 Limit test for sulfates; the sulfate content is not more than 0.2 mg/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 over silica gel, desiccant, R at ambient temperature; it loses not more than 5.0 mg/g.

Assay. Dissolve about 0.3 g, accurately weighed, in 15 ml of neutralized ethanol TS and add 20 ml of water. Titrate with carbonate-free sodium hydroxide (0.1 mol/l) VS, using phenolphthalein/ethanol TS as indicator. Repeat the operation without the substance being examined and make any necessary corrections. Each ml of carbonate-free sodium hydroxide (0.1 mol/l) VS is equivalent to 13.81 mg of C7H6O3.

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