Sodium Stearate

Octadecanoic acid,sodium salt.
Sodium stearate [822-16-2].
»Sodium Stearate is a mixture of sodium stearate (C18H35NaO2)and sodium palmitate (C16H31NaO2),which together constitute not less than 90.0percent of the total content.The content of C18H35NaO2is not less than 40.0percent of the total.Sodium stearate contains small amounts of the sodium salts of other fatty acids.
Packaging and storage— Preserve in well-closed,light-resistant containers.
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 nonluminous flame intensely yellow.
B: Dissolve 25g in 300mLof hot water,add 60mLof 2Nsulfuric 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 105for 20minutes:the solidification temperature of the fatty acids is not less than 54.
Acid value of fatty acids á401ñ: between 196and 211,determined on 1g of the fatty acids obtained in Identificationtest B.
Iodine value of fatty acids á401ñ: not more than 4.0,determined on the fatty acids obtained in Identificationtest B.
Acidity— Heat 50mLof alcohol to the same temperature,±5,as that attained when the pink endpoint is reached in the titration of the test specimen.Add 3drops of phenolphthalein TSand sufficient 0.020Nsodium hydroxide to produce a faint pink color.Add 2.00g of Sodium Stearate,and dissolve with the aid of a small amount of heat:no pink color is produced.Titrate the solution with 0.020Nsodium hydroxide until a pink color is produced:between 1.00mLand 4.25mLof 0.020Nsodium hydroxide is required (between 0.28%and 1.2%as stearic acid).
Loss on drying á731ñ Tare a beaker containing about 1g of washed sand,previously dried at 105,add about 500mg of Sodium Stearate,and again weigh.Add 10mLof alcohol,evaporate the mixture at about 80to dryness,and dry at 105for 4hours:it loses not more than 5.0%of its weight.
Alcohol-insoluble substances— Reflux 1.0g with 25mLof alcohol:it dissolves completely,and the resulting solution is clear or not more than slightly opalescent.
Assay— Proceed with Sodium Stearate as directed in the Assayunder Stearic Acid,using about 100mg of Sodium Stearate,accurately weighed.Determine the percentage of C18H35NaO2in the portion of Sodium Stearate taken by the formula:
in which Ais the area due to the methyl stearate peak,and Bis the sum of the areas of all fatty acid ester peaks in the chromatogram.Similarly,determine the percentage of C16H31NaO2.
Auxiliary Information— Staff Liaison:Ravi Ravichandran,Ph.D.,Senior Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 3080
Phone Number:1-301-816-8330