Propylene Glycol Monostearate
Octadecanoic acid, monoester with 1,2-propanediol. 1,2-Propanediol monostearate ![]() ![]() ![]() » Propylene Glycol Monostearate is a mixture of the propylene glycol mono- and di-esters of stearic and palmitic acids. It contains not less than 90.0 percent 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
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Residue on ignition
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Acid value
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Saponification value
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Hydroxyl value
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Iodine value
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Free glycerin and propylene glycol
Periodic acid solution
Dissolve 5.4 g of periodic acid in 100 mL of water, and add 1900 mL of 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-mL conical flasks add 50.0 mL of Periodic acid solution, then add 50 mL of chloroform and 10 mL of water to two of the flasks and 50 mL of water to the third flask. To each flask add 20 mL of potassium iodide TS, mix gently, and proceed as directed for Procedure, beginning with allow to stand for 1 to 5 minutes. The difference between the volumes of 0.1 N sodium thiosulfate required in the titrations with and without the chloroform does not exceed 100 µL.
Procedure
Melt the Propylene Glycol Monostearate at a temperature not above 55
![]() [3.805N(B
in which 3.805 is the molecular weight of propylene glycol divided by 20; N is the exact normality of the sodium thiosulfate solution; B and T are the volumes, in mL, of sodium thiosulfate consumed in the titrations of the blank solution and test solution, respectively; and W is the weight, in g, of Propylene Glycol Monostearate taken.
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Propylene glycol monoesters
Transfer about 25 g to a 500-mL, round-bottom flask, add 250 mL of alcohol and 7.5 g of potassium hydroxide, and mix. Connect a suitable condenser to the flask, reflux the mixture for 2 hours, cool, and transfer to an 800-mL beaker, rinsing the flask with about 100 mL of 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 250 mL, 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-mL separator. Wash the fatty acids with four 200-mL portions of hot water, and discard the washings. Dry the fatty acids at 105
![]() ![]() ![]() [M(H
calculate M, the average molecular weight of the monoesters, taken by the formula:
![]() (56,110 / A) + 76.10
and calculate F taken by the formula:
![]() 561.1G / 38.05
in which H is the Hydroxyl value of Propylene Glycol Monostearate, G is the content, in percentage, of glycerin and propylene glycol in Propylene Glycol Monostearate, 561.1 and 56,110 are 10 and 1000 times the molecular weight of potassium hydroxide, respectively, 38.05 is one-half of the molecular weight of propylene glycol (76.10), and 18.02 is the molecular weight of water.
Auxiliary Information
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Chromatographic Column
USP32NF27 Page 1329
Pharmacopeial Forum: Volume No. 29(2) Page 479
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.
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