Benzoic Acid

Benzoic Acid BP
C7H6O2 -- 122.1 -- 65-85-0

DEFINITION
Benzoic acid contains not less than 99.0 per cent and not more than the equivalent of 100.5 per cent of benzene carboxylic acid.

CHARACTERS
A white, crystalline powder or colourless crystals, odourless or with a very slight characteristic odour, slightly soluble in water, soluble in boiling water, freely soluble in alcohol and in fatty oils.

IDENTIFICATION
A. Melting point  121C to 124C.
B. Solution S (see Tests) gives reaction (a) of benzoates.

TESTS
Solution S
Dissolve 5.0 g in alcohol and dilute to 100 ml with the same solvent.
Appearance of solution
Solution S is clear and colourless.
Carbonizable substances
Dissolve 0.5 g with shaking in 5 ml of sulphuric acid. After 5 min, the solution is not more intensely coloured than reference solution.
Oxidizable substances
Dissolve 0.2 g in 10 ml of boiling water. Cool, shake and filter. To the filtrate add 1 ml of dilute sulphuric acid and 0.2 ml of 0.02 M potassium permanganate. After 5 min, the solution is still coloured pink.
Halogenated compounds and halides
All glassware used must be chloride-free and may be prepared by soaking overnight  in a 500 g/l solution of nitric acid, rinsed with water and stored full of water. It is recommended that glassware be reserved for this test.
Solution (a) Dissolve 6.7 g of the substance to be examined in a mixture of 40 ml of  1 M sodium hydroxide and 50 ml of alcohol and dilute to 100.0 ml with water. To 10.0 ml of this solution add 7.5 ml of dilute sodium hydroxide solution and 0.125 g of nickel-aluminium alloy and heat on a water-bath for 10 min. Allow to cool to room temperature, filter into a 25 ml volumetric flask and wash with three quantities, each of 2 ml, of alcohol. Dilute the filtrate and washings to 25.0 ml with water.  This solution is used to prepare solution A.
Solution (b) In the same manner, prepare a similar solution without the substance to be examined. This solution is used to prepare solution B.
In four 25 ml volumetric flasks, place separately 10 ml of solution (a), 10 ml of solution (b), 10 ml of chloride standard solution (8 ppm Cl) (used to prepare solution C) and 10 ml of water. To each flask add 5 ml of ferric ammonium sulphate solution, mix and add drop wise and with swirling 2 ml of nitric acid and 5 ml of mercuric thiocyanate solution. Shake. Dilute the contents of each flask  to 25.0 ml with water and allow the solutions to stand in a water-bath at 20 °C for 15 min. Measure at 460 nm the absorbance of solution A using solution B as the compensation liquid, and the absorbance of solution C using the solution  obtained with 10 ml of water as the compensation liquid. The absorbance of solution A is not greater than that of solution C (300 ppm).
Heavy metals
12 ml of solution S complies with limit test B for heavy metals (10 ppm).
Sulphated ash
Not more than 0.1 per cent, determined on 1.0 g.

Benzoic Acid USP Benzoic Acid
C7H6O2 122.12