Propylene glycol

Propylene glycol, known also by the systematic name propane-1,2-diol, is an organic compound (a diol alcohol), usually a tasteless, odorless, and colorless clear oily liquid that is hygroscopic and miscible with water, acetone, and chloroform.

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Chirality

Propylene glycol contains an asymmetrical carbon atom, so it exists in two isomers. The commercial product is a racemic mixture. Pure optical isomers can be obtained by hydration of optically pure propylene oxide.^[1]

Production

Industrially propylene glycol is produced by propylene oxide hydration. Different manufacturers use non-catalytic high-temperature process or catalytic route with acid or alkali as a catalyst. Propylene glycol can also be converted from glycerol, a biodiesel byproduct.

Applications

Propylene glycol is used:

• As a moisturizer in medicines, cosmetics, food, toothpaste, mouth wash, and tobacco products
• As a medical and sexual lubricant (A.K.A. "personal lubricant")
• As an emulsification agent in Angostura and Orange bitters
• As a solvent for food colors and flavourings
• As a humectant food additive, labeled as E number E1520
• As a carrier in fragrance oils
• As a less-toxic antifreeze
• In smoke machines to make artificial smoke for use in firefighters' training and theatrical productions
• In electronic cigarettes to make the produced vapor better resemble cigarette smoke
• In hand sanitizers, antibacterial lotions, and saline solutions
• In cryonics
• As a working fluid in hydraulic presses
• To regulate humidity in a cigar humidor
• As the killing and preserving agent in pitfall traps, usually used to capture ground beetles
• To treat livestock ketosis
• Mountain Dew

Propylene glycol has similar properties as ethylene glycol (MEG). The industrial norm is to replace ethylene glycol by propylene glycol.

Safety

The U.S. Food and Drug Administration has determined that propylene glycol in or on cat food has not been shown by adequate scientific data to be safe for use. Use of propylene glycol in or on cat food causes the feed to be adulterated and in violation of the Federal Food, Drug, and Cosmetic Act. 21CFR589.1001

The U.S. Food and Drug Administration (FDA) has determined propylene glycol to be "generally recognized as safe" for use in food, cosmetics, and medicines. Like ethylene glycol, propylene glycol affects the body's chemistry by increasing the amount of acid. Propylene glycol is metabolized into lactic acid, which occurs naturally as muscles are exercised, while ethylene glycol is metabolized into oxalic acid, which is toxic.

Post menopausal women who require the use of an estrogen cream may notice that brand name creams made with propylene glycol often create extreme, uncomfortable burning along the vulva and perianal area. In these cases, patients can request that a local compounding pharmacy make a "propylene glycol free" cream which is much more tolerable.

Patients with vulvodynia and interstitial cystitis may be especially sensitive to propylene glycol. Women struggling with yeast infections may also notice that some OTC creams can cause intense burning.^[2]

References

1. ^ 1,2-Propanediol. ChemIndustry.ru. Retrieved on 2007-12-28.
2. ^ Elizabeth Vliet MD, Screaming To Be Heard: Hormonal Connections That Women Suspect and Doctors Ignore". M. Evans and Company, Inc. New York 1995

• Merck Index, 11th Edition, 7868

See also

• Ethylene glycol