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 90.0 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 651: not lower than 45.
Residue on ignition 281: not more than 0.5%.
Acid value 401: not more than 4.
Saponification value 401: between 155 and 165.
Hydroxyl value 401: between 160 and 175.
Iodine value 401: not more than 3.
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, and mix. Transfer a 3-g portion, accurately weighed, to a 100-mL beaker, and dissolve in 25 mL of Chloroform. Transfer this solution, with the aid of another 25-mL portion of Chloroform, to a separator, wash the beaker with 25 mL of water, and add the washing to the separator. Insert the stopper, shake vigorously for 30 to 60 seconds, and allow the layers to separate, adding 1 mL to 2 mL of glacial acetic acid, if necessary, to break any emulsion. Transfer the aqueous layer to a glass-stoppered, 500-mL conical flask, wash the chloroform layer with two 25-mL portions of water, combining the washings with the aqueous layer, and discard the chloroform layer. Add, with swirling, 50.0 mL of Periodic acid solution to the solution and to another glass-stoppered, 500-mL conical flask containing 75 mL of water to provide the blank. Allow to stand for 30 to 90 minutes. To each flask add 20 mL of potassium iodide TS, mix gently, and allow to stand for 1 to 5 minutes before titrating. Add 100 mL of water, and titrate with 0.1 N sodium thiosulfate VS until the brown iodine color fades to pale yellow, add 3 mL of 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 3.805 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.
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 for 1 hour, 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 401. 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 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— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, B.A.
(EM105) Excipient Monographs 1
USP32–NF27 Page 1329
Pharmacopeial Forum: Volume No. 29(2) Page 479
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.