Calcium Stearate

Octadecanoic acid,calcium salt.
Calcium stearate [1592-23-0].
»Calcium Stearate is a compound of calcium with a mixture of solid organic acids obtained from fats and consists chiefly of variable proportions of calcium stearate and calcium palmitate.It contains the equivalent of not less than 9.0percent and not more than 10.5percent of calcium oxide (CaO).
Packaging and storage— Preserve in well-closed containers.
Identification—
A: Heat 1g with a mixture of 25mLof water and 5mLof hydrochloric acid:fatty acids are liberated and appear as an oily layer floating on the surface of the liquid.The water layer responds to the tests for Calcium á191ñ.
B: Mix 25g with 200mLof hot water,add 60mLof 2Nsulfuric acid,and heat the mixture,with frequent stirring,until the separated fatty acid layer is clear.Wash the fatty acids with boiling water until free from sulfate,collect them in a small beaker,and warm on a steam bath until the water has separated and the fatty acids are clear.Allow the acids to cool,pour off the water layer,melt the acids,filter into a dry beaker,and dry at 105for 20minutes:the fatty acids so obtained congeal at a temperature not below 54(see Congealing Temperature á651ñ).
Loss on drying á731ñ— Dry it at 105to constant weight,using 2-hour increments of heating:it loses not more than 4.0%of its weight.
Heavy metals á231ñ— Place 2.5g in a porcelain dish,place a 500-mg portion in a second dish to provide the control,and to each add 5mLof a 1in 4solution of magnesium nitrate in alcohol.Cover the dishes with 7.5-cm short-stem funnels so that the stems are straight up.Heat on a hot plate at low heat for 30minutes,then heat at medium heat for 30minutes,and cool.Remove the funnels,add 2mLof Standard Lead Solution(20µg of Pb)to the control,and heat each dish over a suitable burner until most of the carbon is burned off.Cool,add 10mLof nitric acid,and transfer the solutions into 250-mLbeakers.Add 5mLof 70%perchloric acid,cautiously evaporate to dryness,add 2mLof hydrochloric acid to the residues,and wash down the insides of the beakers with water.Evaporate carefully to dryness again,swirling near the dry point to avoid spattering.Repeat the hydrochloric acid treatment,then cool,and dissolve the residues in about 10mLof water.To each solution add 1drop of phenolphthalein TSand add sodium hydroxide TSuntil the solutions just turn pink,then add 3Nhydrochloric acid until the solutions become colorless.Add 1mLof 1Nacetic acid and a small amount of charcoal to each solution,and filter through filter paper into 50-mLcolor-comparison tubes.Wash with water,dilute with water to 40mL,add 1.2mLof thioacetamide-glycerin base TSand 2mLof pH3.5Acetate Bufferto each tube,and allow to stand for 5minutes:the color of the test solution does not exceed that of the control.The limit is 10µg per g.
Assay— Boil about 1.2g of Calcium Stearate,accurately weighed,with 50mLof 1Nsulfuric acid for about 3hours using a watch glass cover to avoid splattering,or until the separated fatty acid layer is clear,adding water,if necessary,to maintain the original volume.[NOTE—Stirring may be helpful in obtaining a clear layer and decreasing extraction time.]Cool,filter,and wash the filter and the flask thoroughly with water until the last washing is not acid to litmus.Neutralize the filtrate with 1Nsodium hydroxide to litmus.While stirring,preferably with a magnetic stirrer,titrate with 0.05Medetate disodium VSas follows.Add about 30mLfrom a 50-mLburet,then add 15mLof 1Nsodium hydroxide and 300mg of hydroxy naphthol blue,and continue the titration to a blue endpoint.Each mLof 0.05Medetate disodium is equivalent to 2.804mg of CaO.
Auxiliary Information— Staff Liaison:Catherine Sheehan,B.Sc.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 2970
Phone Number:1-301-816-8262