Green Soap
»Green Soap is a potassium soap made by the saponification of suitable vegetable oils,excluding coconut oil and palm kernel oil,without the removal of glycerin.
Green Soap may be prepared as follows:
The Vegetable Oil 380g
Oleic Acid 20g
Potassium Hydroxide (total alkali
85percent)		 91.7g
Glycerin 50mL
Purified Water,a sufficient quantity
to make about		 1000g
Mix the oil and the Oleic Acid,and heat the mixture to about 80.Dissolve the Potassium Hydroxide in a mixture of the Glycerin and 100mLof Purified Water,and add the solution,while it is still hot,to the hot oil.Stir the mixture vigorously until emulsified,then heat while continuing the stirring,until the mixture is homogeneous and a test portion will dissolve to give a clear solution in hot water.Add hot purified water to make the product weigh 1000g,continuing the stirring until the Soap is homogeneous.
Packaging and storage— Preserve in well-closed containers.
Water— Place about 5g of Soap,quickly weighed to the nearest centigram,in the distilling flask of the apparatus for Moisture Method by Toluene Distillation á921ñ.(The Soap is most conveniently weighed in a boat of metal foil,of a size that will just pass through the neck of the flask.)Place 250mLof toluene and 10g of anhydrous barium chloride in the flask,connect the flask through a ground-glass joint to the distilling apparatus,fill the receiving tube with toluene,and determine the water as directed,beginning with “Heat the flask gently.”The volume of water found corresponds to not more than 52.0%by weight of the Soap taken.
Alcohol-insoluble substances— Dissolve about 5g of Soap,rapidly and accurately weighed,in 100mLof hot neutralized alcohol,collect the residue,if any,on a tared filter,thoroughly wash it with hot neutralized alcohol,and dry at 105for 1hour:the weight of the residue so obtained is not more than 3.0%of the weight of the Soap taken.Retain the solution for the test for Free alkali hydroxides,and retain the residue for the test for Alkali carbonates.
Free alkali hydroxides— To the combined filtrate and washings obtained in the test for Alcohol-insoluble substancesadd 0.5mLof phenolphthalein TS.If a pink color is produced,titrate the solution with 0.1Nsulfuric acid VSuntil the pink color is just discharged.Each mLof 0.1Nsulfuric acid is equivalent to 5.611mg of KOH.The volume of 0.1Nsulfuric acid VSconsumed corresponds to not more than 0.25%of KOH.
Alkali carbonates— Wash the filter containing the Alcohol-insoluble substanceswith 50mLof boiling water,cool,add methyl orange TS,and titrate the filtrate with 0.1Nsulfuric acid VS.Not more than 0.5mLof 0.10Nsulfuric acid per g of Soap originally taken is required (0.35%as K2CO3).
Unsaponified matter— Asolution of Soap in hot water (1in 20)is nearly clear.
Characteristics of the liberated fatty acids— Dissolve about 30g of Soap in 300mLof hot water in a beaker,add gradually 60mLof 2Nsulfuric acid,and heat on a steam bath until the liberated acids form a transparent layer.Decant the fatty acids into a separator,and wash them with 50-mLportions of hot water until the last washing,when cool,is neutral to methyl orange TS.Transfer the fatty acids to a dry beaker,and allow them to stand in a warm oven until any water that may be present has separated.Then filter the acids through a dry filter in the warm oven.Determine the Acid Value(see Fats and Fixed Oils á401ñ)of about 1g,accurately weighed,of the fatty acids:it is not more than 205.Determine the Iodine Value(see Fats and Fixed oils á401ñ)of 150to 200mg,accurately weighed,of the fatty acids:it is not less than 85.
Auxiliary Information— Staff Liaison:Behnam Davani,Ph.D.,MBA,Senior Scientist
Expert Committee:(PA7)Pharmaceutical Analysis 7
USP28–NF23Page 919
Phone Number:1-301-816-8394