Propylene Glycol Monostearate
Octadecanoic acid,monoester with 1,2-propanediol.
1,2-Propanediol monostearate [1323-39-3].
»Propylene Glycol Monostearate is a mixture of the propylene glycol mono-and di-esters of stearic and palmitic acids.It contains not less than 90.0percent of monoesters of saturated fatty acids,chiefly propylene glycol monostearate (C21H42O3)and propylene glycol monopalmitate (C19H38O3).
Packaging and storage—
Preserve in well-closed containers.
Congealing temperature á651ñ:
not lower than 45
.
.
Residue on ignition á281ñ:
not more than 0.5%.
Acid value á401ñ:
not more than 4.
Saponification value á401ñ:
between 155and 165.
Hydroxyl value á401ñ:
between 160and 175.
Iodine value á401ñ:
not more than 3.
Free glycerin and propylene glycol—
Periodic acid solution—
Dissolve 5.4g of periodic acid in 100mLof water,and add 1900mLof glacial acetic acid.Store in a glass-stoppered bottle,protected from light.
Chloroform—
Use chloroform that meets the following additional requirement.To each of three glass-stoppered,500-mLconical flasks add 50.0mLof Periodic acid solution,then add 50mLof chloroform and 10mLof water to two of the flasks and 50mLof water to the third flask.To each flask add 20mLof potassium iodide TS,mix gently,and proceed as directed for Procedure,beginning with “allow to stand for 1to 5minutes.”The difference between the volumes of 0.1Nsodium thiosulfate required in the titrations with and without the chloroform does not exceed 100µL.
Procedure—
Melt the Propylene Glycol Monostearate at a temperature not above 55,and mix.Transfer a 3-g portion,accurately weighed,to a 100-mLbeaker,and dissolve in 25mLof Chloroform.Transfer this solution,with the aid of another 25-mLportion of Chloroform,to a separator,wash the beaker with 25mLof water,and add the washing to the separator.Insert the stopper,shake vigorously for 30to 60seconds,and allow the layers to separate,adding 1mLto 2mLof glacial acetic acid,if necessary,to break any emulsion.Transfer the aqueous layer to a glass-stoppered,500-mLconical flask,wash the chloroform layer with two 25-mLportions of water,combining the washings with the aqueous layer,and discard the chloroform layer.Add,with swirling,50.0mLof Periodic acid solutionto the solution and to another glass-stoppered,500-mLconical flask containing 75mLof water to provide the blank.Allow to stand for 30to 90minutes.To each flask add 20mLof potassium iodide TS,mix gently,and allow to stand for 1to 5minutes before titrating.Add 100mLof water,and titrate with 0.1Nsodium thiosulfate VSuntil the brown iodine color fades to pale yellow,add 3mLof starch TS,and continue the titration to the disappearance of the blue color.Propylene Glycol Monostearate contains not more than 1.0%of free glycerin and propylene glycol,calculated as propylene glycol taken by the formula:
,and mix.Transfer a 3-g portion,accurately weighed,to a 100-mLbeaker,and dissolve in 25mLof Chloroform.Transfer this solution,with the aid of another 25-mLportion of Chloroform,to a separator,wash the beaker with 25mLof water,and add the washing to the separator.Insert the stopper,shake vigorously for 30to 60seconds,and allow the layers to separate,adding 1mLto 2mLof glacial acetic acid,if necessary,to break any emulsion.Transfer the aqueous layer to a glass-stoppered,500-mLconical flask,wash the chloroform layer with two 25-mLportions of water,combining the washings with the aqueous layer,and discard the chloroform layer.Add,with swirling,50.0mLof Periodic acid solutionto the solution and to another glass-stoppered,500-mLconical flask containing 75mLof water to provide the blank.Allow to stand for 30to 90minutes.To each flask add 20mLof potassium iodide TS,mix gently,and allow to stand for 1to 5minutes before titrating.Add 100mLof water,and titrate with 0.1Nsodium thiosulfate VSuntil the brown iodine color fades to pale yellow,add 3mLof starch TS,and continue the titration to the disappearance of the blue color.Propylene Glycol Monostearate contains not more than 1.0%of free glycerin and propylene glycol,calculated as propylene glycol taken by the formula:
[3.805N(B-T)]/W,
in which 3.805is the molecular weight of propylene glycol divided by 20;Nis the exact normality of the sodium thiosulfate solution;Band Tare the volumes,in mL,of sodium thiosulfate consumed in the titrations of the blank solution and test solution,respectively;and Wis the weight,in g,of Propylene Glycol Monostearate taken.
Propylene glycol monoesters—
Transfer about 25g to a 500-mL,round-bottom flask,add 250mLof alcohol and 7.5g of potassium hydroxide,and mix.Connect a suitable condenser to the flask,reflux the mixture for 2hours,cool,and transfer to an 800-mLbeaker,rinsing the flask with about 100mLof water and combining the rinsing with the mixture in the beaker.Heat on a steam bath to evaporate the alcohol,adding water occasionally to replace the alcohol,and continue the evaporation until the odor of alcohol can no longer be detected.Adjust the volume,with hot water,to about 250mL,neutralize with a mixture of equal volumes of sulfuric acid and water,noting the volume used,and add a 10%excess of the dilute acid.Heat with stirring until the fatty acid layer separates,and transfer the fatty acids to a 500-mLseparator.Wash the fatty acids with four 200-mLportions of hot water,and discard the washings.Dry the fatty acids at 105for 1hour,cool,and determine the Acid value,A,on a 1-g portion,accurately weighed,as directed for Acid (Free Fatty Acids)under Fats and Fixed Oils á401ñ.Calculate the percentage of propylene glycol monoesters taken by the formula:
for 1hour,cool,and determine the Acid value,A,on a 1-g portion,accurately weighed,as directed for Acid (Free Fatty Acids)under Fats and Fixed Oils á401ñ.Calculate the percentage of propylene glycol monoesters taken by the formula:
[M(H-F)]/561.1;
calculate M,the average molecular weight of the monoesters,taken by the formula:
(56,110/A)+76.10-18.02;
and calculate Ftaken by the formula:
561.1G/38.05,
in which His the Hydroxyl valueof Propylene Glycol Monostearate,Gis the content,in percentage,of glycerin and propylene glycol in Propylene Glycol Monostearate,561.1and 56,110are 10and 1000times the molecular weight of potassium hydroxide,respectively,38.05is one-half of the molecular weight of propylene glycol (76.10),and 18.02is the molecular weight of water.
Organic volatile impurities,Method IVá467ñ:
meets the requirements.
Auxiliary Information—
Staff Liaison:Justin Lane,B.S.,Scientific Associate
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 3069
Pharmacopeial Forum:Volume No.29(2)Page 479
Phone Number:1-301-816-8323