Sodium Stearate

Sodium Stearate

Sodium Stearate BP

Action and use
Excipient

DEFINITION
Mixture of sodium salts of different fatty acids consisting mainly of stearic (octadecanoic) acid [C17H35COONa] and palmitic (hexadecanoic) acid [C15H31COONa].
Content:
sodium: 7.4 per cent to 8.5 per cent (dried substance);
stearic acid in the fatty acid fraction: minimum 40 per cent;
sum of stearic acid and palmitic acid in the fatty acid fraction: minimum 90 per cent.

CHARACTERS
Appearance: White or yellowish, fine powder, greasy to the touch.
Solubility: Slightly soluble in water and in ethanol (96 per cent).

IDENTIFICATION
First identification C, D.
Second identification A, B, D.
A. Freezing point Minimum 53°C for the residue obtained in the preparation of solution S (see Tests).
B. Acid value 195 to 210, determined on 0.200 g of the residue obtained in the preparation of solution S dissolved in 25 ml of the prescribed mixture of solvents.
C. Examine the chromatograms obtained in the assay of stearic acid and palmitic acid.
Results The 2 principal peaks in the chromatogram obtained with the test solution are similar in retention time and size to the 2 principal peaks in the chromatogram obtained with the reference solution.
D. Solution S gives reaction of sodium.

TESTS
Solution S
To 10.0 g Sodium Stearate add 100 ml of peroxide-free ether and 80 ml of acetic acid. Boil under a reflux condenser until dissolution is complete. Allow to cool. In a separating funnel, separate the aqueous layer and shake the ether layer with 2 quantities, each of 8 ml, of acetic acid. Combine the aqueous layers, wash with 30 ml of peroxide-free ether and dilute to 100 ml with distilled water (solution S). Evaporate the ether layers to dryness on a water-bath and dry the residue at 100-105C.
Acidity or alkalinity
Suspend 2.0 g in 50 ml of previously neutralized ethanol (96 per cent). Heat under reflux to dissolve and add 3 drops of phenolphthalein solution; the solution is colourless. Not less than 0.60 ml and not more than 0.85 ml of 0.1 M sodium hydroxide is required to change the colour of the indicator.
Chlorides
Maximum 0.2 per cent.
Sulphate
Maximum 0.3 per cent.
Nickel
Maximum 5.0 ppm.
Atomic absorption spectrometry.
To pass the test.
Loss on drying
Maximum 5.0 per cent.
Microbial contamination
Total viable aerobic count not more than 103 micro-organisms per gram, determined by plate count. It complies with the test for Escherichia coli.

Sodium Stearate USP NF

Sodium Stearate
Octadecanoic acid, sodium salt.
Sodium stearate [CAS 822-16-2]

Sodium Stearate is a mixture of sodium stearate (C18H35NaO2) and sodium palmitate (C16H31NaO2), which together constitute not less than 90.0 percent of the total content. The content of C18H35NaO2 is not less than 40.0 percent of the total. Sodium stearate contains small amounts of the sodium salts of other fatty acids.

USP Reference standards—
USP Palmitic Acid RS
USP Stearic Acid RS

Identification—
A: When heated, it fuses. At a high temperature it decomposes, emitting flammable vapors and the odor of burning fat, finally leaving a residue that, when moistened with water, is alkaline to litmus paper, effervesces with acids, and colors a non-luminous flame intensely yellow.
B: Dissolve 25 g in 300 mL of hot water, add 60 mL of 2 N sulfuric acid, and heat the solution, with frequent stirring, until the separated fatty acid layer is clear. Wash the fatty acids with boiling water until they are free from sulfate, collect in a small beaker, and warm on a steam bath until the water has settled and the fatty acids are clear. Allow the acids to cool, pour off the water layer, then melt the acids, filter into a dry beaker while hot, and dry at 105 for 20 minutes: the solidification temperature of the fatty acids is not less than 54.
Acid value of fatty acids: between 196 and 211, determined on 1 g of the fatty acids obtained in Identification test B.
Iodine value of fatty acids: not more than 4.0, determined on the fatty acids obtained in Identification test B.
Acidity— Heat 50 mL of alcohol to the same temperature, ±5 , as that attained when the pink endpoint is reached in the titration of the test specimen. Add 3 drops of phenolphthalein TS and sufficient 0.020 N sodium hydroxide to produce a faint pink color. Add 2.00 g of Sodium Stearate, and dissolve with the aid of a small amount of heat: no pink color is produced. Titrate the solution with 0.020 N sodium hydroxide until a pink color is produced: between 1.00 mL and 4.25 mL of 0.020 N sodium hydroxide is required (between 0.28% and 1.2% as stearic acid).
Loss on drying— Tare a beaker containing about 1 g of washed sand, previously dried at 105 , add about 500 mg of Sodium Stearate, and again weigh. Add 10 mL of alcohol, evaporate the mixture at about 80 to dryness, and dry at 105 for 4 hours: it loses not more than 5.0% of its weight.
Alcohol-insoluble substances— Reflux 1.0 g with 25 mL of alcohol: it dissolves completely, and the resulting solution is clear or not more than slightly opalescent.

Certifications :
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