PROPYL p-HYDROXYBENZOATE

Prepared at the 44th JECFA (1995), published in FNP 52 Add 3 (1995) superseding specifications prepared by the 17th JECFA (1974), published in FNP 4 (1978)

SYNONYMS

Propylparaben, propyl p-oxybenzoate; INS No. 216

DEFINITION

Chemical names

Propyl p-hydroxybenzoate, n-propyl ester of p-hydroxybenzoic acid

C.A.S. number

94-13-3

Chemical formula

C₁₀H₁₂O₃

Structural formula

Formula weight

180.21

Assay

Not less than 99.0% on the dried basis

DESCRIPTION

Almost odourless, small, colourless crystals or a white, crystalline powder

FUNCTIONAL USES

Preservative

CHARACTERISTICS

IDENTIFICATION

Solubility

Freely soluble in ethanol, ether, chloroform and propylene glycol

Melting range

95 ^o - 98^o

Test for p-hydroxybenzoate

Melting range of p-hydroxybenzoic acid derived from the sample is 212-217^o

To 0.5 g of the sample add 10 ml of sodium hydroxide TS. Boil for 30 min and concentrate to about 5 ml. Cool, acidify with dilute sulfuric acid TS, collect the precipitate on a filter, and wash thoroughly with water. Dry in a desiccator over sulfuric acid. determine the melting range of p-hydroxybenzoic acid so obtained.

PURITY

Loss on drying

Not more than 0.5% (over silical gel, 5 h)

Sulfated ash

Not more than 0.05%

Test 2 g of the sample (Method I)

Acidity

Heat 750 mg of the sample with 15 ml of water at 80^o for 1 min, cool, and filter. The filtrate should be acid or neutral to litmus. To 10 ml of the filtrate add 0.2 ml of 0.1 N sodium hydroxide and 2 drops of methyl red TS. The solution should be yellow without even a light cast of pink.

p-Hydroxybenzoic acid and salicylic acid

Dissolve 0.5 g of the sample, accurately weighed, in 30 ml of ether, add 20 ml of a 1 in 100 sodium hydrogen carbonate solution, shake, and separate the water layer. Wash the water layer with two 20 ml portions of ether, add 5 ml of dilute sulfuric acid and 30 ml of ether, and shake. Separate the ether layer, and shake with about 10 ml of water. Filter the ether layer, and wash the vessel and the filter with a small amount of ether. Combine the washings and the filtrate, evaporate ether on a water bath, and dry the residue over sulfuric acid to constant weight. The weight of the residue should not exceed 5 mg. Dissolve any residue in 25 ml of water, heat to about 70^o, filter, and add a few drops of dilute ferric chloride TS. No violet to reddish violet colour should be produced.

Arsenic

Not more than 3 mg/kg (Method II)

Heavy metals

Not more than 10 mg/kg

Test 2 g of the sample as directed in the Limit Test (Method II)

METHOD OF ASSAY

Weigh, to the nearest mg, 2 g of the dried sample and transfer into a flask. Add 40 ml of N sodium hydroxide and rinse the sides of the flask with water. Cover with a watch glass, boil gently for 1 h and cool. Add 5 drops of bromothymol blue TS and titrate the excess sodium hydroxide with N sulfuric acid, matching the colour against a buffer solution (pH 6.5) containing the same proportion of indicator. Perform a blank determination with the reagents and make any necessary correction. Each ml of N sodium hydroxide is equivalent to 180.2 mg of C₁₀H₁₂O₃.