Propylene glycol

Prepared at the 49th JECFA (1997)
superseding specifications prepared at the 46th JECFA (1996),
published in FNP 52 Addendum 4 (1996)

SYNONYMS

Propanediol, Methyl glycol, INS No. 1520

DEFINITION

Chemical names

Propane-1,2-diol, 1,2-dihydroxypropane

C.A.S. number

57-55-6

Chemical formula

C₃H₈O₂

Structural formula

Molecular weight

76.10

Assay

Not less than 99.5% on the anhydrous basis

DESCRIPTION

Clear, colourless, hygroscopic, viscous liquid

FUNCTIONAL USES

Solvent, glazing agent, humectant

CHARACTERISTICS

IDENTIFICATION

Solubility

Soluble in water, ethanol and acetone

Infrared absorption

The infrared spectrum of a potassium bromide dispersion of the sample corresponds with the infrared spectrum in the Appendix

PURITY

Distillation range

99% v/v distils between 185-189°

Specific gravity

: 1.035 - 1.040

Water

Not more than 1.0% (Karl Fischer)

Sulfated ash

Not more than 0.07%
Proceed as directed under the test for Ash (Sulfated ash, Method II), using 5 g of the sample

Heavy metals

Not more than 10 mg/kg
A solution of 2 g of the sample in 25 ml of water meets the requirements of the Limit Test (Method I)

Free acid

Passes test
Add 3-6 drops of phenol red TS to 50 ml water, then add 0.1N sodium hydroxide until solution remains red for 30 sec. To this solution add about 50 g of the sample accurately weighed. Titrate with 0.0 IN sodium hydroxide until the original red colour returns and remains for 15 sec. Not more than 1.67 ml of 0.0 IN sodium hydroxide are consumed by a sample of 50.0g.

METHOD OF ASSAY

Inject a 10-m l portion of the sample into a suitable gas chromatograph equipped with a thermal conductivity detector and a stainless steel column, 1-m x 1/4-in, packed with 4% Carbowax 20 M on 40/60-mesh Chromosorb T, or equivalent materials. The carrier gas is helium flowing at 75 ml/min. The injection port temperature is 240°, the column temperature 120 to 200°, programmed at a rate of 5° per min, and the block temperature 250°. Under the conditions described, the approximate retention time for propylene glycol is 5.7 min, and 8.2, 9.0, and 10.2 min for the three isomers of dipropylene glycol, respectively. Measure the area under all peaks by any convenient means, calculate the normalized area percentage of propylene glycol, and report as weight percentage.

APPENDIX

Infrared spectrum: Propylene glycol

Infrared spectrum from Merck FT-IR Atlas through courtesy of Dr. K.G.R. Pachler, Mr. F. Matlok and Dr. H-U. Gremlich, c/o Merck, Darmstadt, and VCII Verlagsgesellschaft GmbH, Weinheim, Germany.

SYNONYMS	Propanediol, Methyl glycol, INS No. 1520
DEFINITION
Chemical names	Propane-1,2-diol, 1,2-dihydroxypropane
C.A.S. number	57-55-6
Chemical formula	C₃H₈O₂
Structural formula
Molecular weight	76.10
Assay	Not less than 99.5% on the anhydrous basis
DESCRIPTION	Clear, colourless, hygroscopic, viscous liquid
FUNCTIONAL USES	Solvent, glazing agent, humectant
CHARACTERISTICS
IDENTIFICATION
Solubility	Soluble in water, ethanol and acetone
Infrared absorption	The infrared spectrum of a potassium bromide dispersion of the sample corresponds with the infrared spectrum in the Appendix
PURITY
Distillation range	99% v/v distils between 185-189°
Specific gravity	: 1.035 - 1.040
Water	Not more than 1.0% (Karl Fischer)
Sulfated ash	Not more than 0.07% Proceed as directed under the test for Ash (Sulfated ash, Method II), using 5 g of the sample
Heavy metals	Not more than 10 mg/kg A solution of 2 g of the sample in 25 ml of water meets the requirements of the Limit Test (Method I)
Free acid	Passes test Add 3-6 drops of phenol red TS to 50 ml water, then add 0.1N sodium hydroxide until solution remains red for 30 sec. To this solution add about 50 g of the sample accurately weighed. Titrate with 0.0 IN sodium hydroxide until the original red colour returns and remains for 15 sec. Not more than 1.67 ml of 0.0 IN sodium hydroxide are consumed by a sample of 50.0g.
METHOD OF ASSAY	Inject a 10-m l portion of the sample into a suitable gas chromatograph equipped with a thermal conductivity detector and a stainless steel column, 1-m x 1/4-in, packed with 4% Carbowax 20 M on 40/60-mesh Chromosorb T, or equivalent materials. The carrier gas is helium flowing at 75 ml/min. The injection port temperature is 240°, the column temperature 120 to 200°, programmed at a rate of 5° per min, and the block temperature 250°. Under the conditions described, the approximate retention time for propylene glycol is 5.7 min, and 8.2, 9.0, and 10.2 min for the three isomers of dipropylene glycol, respectively. Measure the area under all peaks by any convenient means, calculate the normalized area percentage of propylene glycol, and report as weight percentage.