POTASSIUM BENZOATE

Prepared at the 46th JECFA (1996), published in FNP 52 Add 4 (1996) superseding specifications prepared at the 17th JECFA (1974), published in FNP 4 (1978)

SYNONYMS

INS No. 212

DEFINITION

Chemical names

Potassium benzoate, potassium salt of benzenecarboxylic acid, potassium salt of phenylcarboxylic acid

C.A.S. number

582-25-2 (anhydrous)

Chemical formula

C₇H₅KO₂ · 3H₂O

Structural formula

Formula weight

160.22 (anhydrous)

214.27 (trihydrate)

Assay

Not less than 99.0% on the dried basis

DESCRIPTION

White crystalline powder

FUNCTIONAL USES

Antimicrobial preservative

CHARACTERISTICS

IDENTIFICATION

Solubility

Freely soluble in water, soluble in ethanol

Test for benzoate

Passes test

Use a 10% solution of the sample

Test for potassium

Passes test

Use a 10% solution of the sample

PURITY

Loss on drying

Not more than 26.5% (105^o, 4 h)

Acidity or alkalinity

Dissolve 2 g of the sample, weighed to the nearest mg, in 20 ml of freshly boiled water. Not more than 0.5 ml of either 0.1N sodium hydroxide or 0.1N hydrochloric acid should be required for neutralization, using phenolphthalein TS as indicator.

Readily carbonizable substances

Dissolve 0.5 g of the sample, weighed to the nearest mg, in 5 ml of

sulfuric acid TS. The colour produced should not be darker than a light pink ("Matching Fluid Q")

Chlorinated organic compounds

Not more than 0.07% (as chlorine)

Test 0.25 g of the sample using 0.5 ml of 0.01N hydrochloric acid in the control

Readily oxidizable substances

Add 1.5 ml of sulfuric acid to 100 ml of water, heat to boiling and add 0.1N potassium permanganate, dropwise, until the pink colour persists for 30 sec. Dissolve 1 g of the sample, weighed to the nearest mg, in the heated solution, and titrate with 0.1N potassium permanganate to a pink colour that persists for 15 sec. Not more than 0.5 ml should be required.

Heavy metals

Not more than 10 mg/kg

Weigh 4 g of the sample to the nearest mg and dissolve in 40 ml of water. Add dropwise, with vigorous stirring, 10 ml of dilute hydrochloric acid TS and filter. A 25-ml portion of the filtrate meets the requirements of the Limit Test (Method I).

METHOD OF ASSAY

Weigh to the nearest 0.1 mg, 2.5 to 3 g of the dried sample, and transfer to a 250-ml Erlenmeyer flask. Add 50 ml of water to dissolve the sample. Neutralize the solution, if necessary, with 0.1N hydrochloric acid, using phenolphthalein TS as indicator. Add 50 ml of ether and a few drops of bromophenol blue TS and titrate with 0.5N hydrochloric acid, shaking constantly the flask, until the colour of the indicator begins to change. Transfer the lower aqueous layer to another flask. Wash the ethereal layer with 10 ml of water, and add the washing and an additional 20 ml of ether to the separated aqueous layer. Complete the titration with the 0.5N hydrochloric acid, shaking constantly the flask. Each ml of 0.5N hydrochloric acid is equivalent to 80.11 mg of C₇H₅KO₂.