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IUPAC name	[show] propane-1,2-diol
Other names	propylene glycol, 1,2-propanediol, 1,2-Dihydroxypropane, methyl ethyl glycol (MEG), methylethylene glycol, PG, Sirlene, Dowfrost

Other names: 1,2-Propanediol; α-Propylene glycol; Methyl glycol; Methylethyl glycol; Methylethylene glycol; Monopropylene glycol; PG 12; Sirlene; 1,2-Dihydroxypropane; 1,2-Propylene Glycol; 2-Hydroxypropanol; 2,3-Propanediol; Propane-1,2-diol; Dowfrost; Propylene glycol usp; 1,2-Propylenglykol; Solar winter ban; Sentry Propylene Glycol; Isopropylene glycol; Ucar 35; Solargard P; Aliphatic alcohol; Chilisa FE; Ilexan P; Inhibited 1,2-propylene glycol; Prolugen; Propanediol; Trimethyl glycol; 1,2-Propandiol; 1,2-propanediol (propylene glycol); propylene glycol (1,2-propanediol); propylenglycol

CAS Registry Number: 57-55-6

Chirality

Propylene glycol contains an asymmetrical carbon atom, so it exists in two stereoisomers. The commercial product is a racemic mixture. Pure optical isomers can be obtained by hydration of optically pure propylene oxide.^[2]

Production

Industrially propylene glycol is produced by propylene oxide hydration.^[3] Different manufacturers use either non-catalytic high-temperature process at 200 °C (392 °F) to 220 °C (428 °F), or a catalytic method, which proceeds at 150 °C (302 °F) to 180 °C (356 °F) in the presence of ion exchange resin or a small amount of sulfuric acid or alkali.

Final products contain 20% 1,2-propanediol, 1.5% of dipropylene glycol and small amounts of other polypropylene glycols.^[4] Propylene glycol can also be converted from glycerol, a biodiesel byproduct.

Propylene glycol has properties similar to those of ethylene glycol (monoethylene glycol, or MEG). (Note: Infrequently propylene glycol may also use the acronym MEG, but as an abbreviation of methyl ethyl glycol- the industry standard acronym for propylene glycol is PG or MPG (monopropylene glycol). The industrial norm is to replace ethylene glycol with propylene glycol when safer properties are desired.

Applications

Propylene glycol is used:

As a solvent in many pharmaceuticals, including oral, injectable and topical formulations. Notably, diazepam, which is insoluble in water, uses propylene glycol as its solvent in its clinical, injectable form.^[5]
As a moisturizer in medicines, cosmetics, food, toothpaste, mouth wash, and tobacco products
In electronic cigarettes to deliver vaporized nicotine
As an emulsification agent in Angostura and orange bitters
As a solvent for food colors and flavorings
As an ingredient, along with wax and gelatin, in the production of paintballs
As a humectant food additive, labeled as E number E1520
As a cooling agent for beer and wine glycol jacketed fermentation tanks
As a carrier in fragrance oils
As an ingredient in massage oils
As a less-toxic antifreeze
As a solvent used in mixing photographic chemicals, such as film developers
In smoke machines to make artificial smoke for use in firefighters' training and theatrical productions
In hand sanitizers, antibacterial lotions, and saline solutions
In cryonics
As a working fluid in hydraulic presses
As a coolant in liquid cooling systems
To regulate humidity in a cigar humidor
As the killing and preserving agent in pitfall traps, usually used to capture ground beetles
As an additive to pipe tobacco to prevent dehydration.
To treat livestock ketosis
As the main ingredient in deodorant sticks.
To de-ice aircraft.^[6]
UV Blacklite Tattoo Ink

Safety

Potential health effects

Eye: Causes mild eye irritation. Contact may cause irritation, tearing, and burning pain.
Skin: Causes moderate skin irritation. Contact with the skin may cause erythema, dryness, and defatting.
Ingestion: May cause gastrointestinal irritation with nausea, vomiting and diarrhea. Low hazard for usual industrial handling. May cause hemoglobinuric nephrosis. May cause changes in surface EEG.
Inhalation: Low hazard for usual industrial handling. May cause respiratory tract irritation.
Chronic: May cause reproductive and fetal effects. Laboratory experiments have resulted in mutagenic effects. Exposure to large doses may cause central nervous system depression. Chronic ingestion may cause lactic acidosis and possible seizures.

The oral toxicity of propylene glycol is very low, and large quantities are required to incur the dangerous effects described above. The potential for long-term toxicity is also low. In one study, rats were provided with feed containing as much as 5% PG over a period of 104 weeks and they showed no apparent ill effects.^[7] Because of its low chronic oral toxicity, propylene glycol is generally recognized as safe (GRAS) for use as a direct food additive. Cases of propylene glycol poisoning are related to either inappropriate intravenous use or accidental ingestion of large quantities by children.^[8]

Serious toxicity will occur only at plasma concentrations over 4g/L, which requires extremely high intake over a relatively short period of time.^[9] It would be nearly impossible to reach toxic levels by consuming foods or supplements, which contain at most 1g/kg of PG. Propylene glycol is metabolized into pyruvic acid, which is a normal part of the glucose metabolism process and is readily converted to energy.

Veterinary data indicates that propylene glycol is toxic to 50% of dogs at doses of 9mL/kg, although the figure is higher for most laboratory animals (LD₅₀ at levels of 20mL/kg).^[10] However, it may be toxic to cats in ways not seen in other animals. 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. If propylene glycol is used in or on cat food, the food is considered adulterated and in violation of the Federal Food, Drug, and Cosmetic Act.^[11]

Prolonged contact with propylene glycol is essentially non-irritating to the skin. Undiluted propylene glycol is minimally irritating to the eye, and can produce slight transient conjunctivitis (the eye recovers after the exposure is removed). Exposure to mists may cause eye irritation, as well as upper respiratory tract irritation. Inhalation of the propylene glycol vapors appears to present no significant hazard in ordinary applications. However, limited human experience indicates that inhalation of propylene glycol mists could be irritating to some individuals. Therefore inhalation exposure to mists of these materials should be avoided. Some research has suggested that propylene glycol not be used in applications where inhalation exposure or human eye contact with the spray mists of these materials is likely, such as fogs for theatrical productions or antifreeze solutions for emergency eye wash stations.^[12]

Propylene glycol does not cause sensitization and it shows no evidence of being a carcinogen or of being genotoxic.^[13]^[14]

There is limited evidence that intravenous injection of PG can cause adverse responses in a small number of people. A Clinical Journal of Medicine article describes two cases of adult men experiencing psychosis from use of injected phenytoin that contained PG as a solvent. Their symptoms resolved when they were switched to a phenytoin formulation without PG.^{[citation
needed]}

Allergic reaction

Research has suggested that individuals who cannot tolerate propylene glycol probably experience a special form of irritation, but that they only rarely develop allergic contact dermatitis. Other investigators believe that the incidence of allergic contact dermatitis to propylene glycol may be greater than 2% in patients with eczema.^[15]

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.^[16]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.

Possible air germicide

Studies conducted in 1942 by Dr. Oswald Hope Robertson of University of Chicago's Billings Hospital showed vaporized propylene glycol inhalation in laboratory mice may prevent pneumonia, influenza, and other respiratory diseases. Additional studies in monkeys and other animals were undertaken to determine longterm effects, especially the potential for accumulation in the lungs.^[17]

References

^ Merck Index, 11th Edition, 7868.
^ "1,2-Propanediol". ChemIndustry.ru. http://chemindustry.ru/1,2-Propanediol.php. Retrieved 2007-12-28.
^ Chauvel, Alain; Lefebvre, Gilles. Petrochemical Processes (Volume 1: Synthesis-Gas Derivatives and Major Hydrocarbons). Editions Technip. pp. 26. ISBN 978-2-7108-0562-5.
^ 1,2-propanediol: chemical product info at CHEMINDUSTRY.RU
^ "Janusz Szajewski, MD , Warsaw Poison Control Centre (August, 1991). "Propylene glycol (PIM 443)". IPCS INChem. http://www.inchem.org/documents/pims/chemical/pim443.htm. Retrieved July 2, 2009.
^ http://pubs.acs.org/cen/whatstuff/stuff/7901scit5.html
^ Gaunt, IF, Carpanini, FMB, Grasso, P and Lansdown, ABG, Long-term toxicity of propylene glycol in rats, Food and Cosmetics Toxicology, Apr. 1972, 10(2), pages 151 - 162.
^ National Library of Medicine;.Propylene glycol is used in antifreezes Human Toxicity Excerpts: CAS Registry Number: 57-55-6 (1,2-Propylene Glycol). Selected toxicity information from HSDB. 2005.
^ Flanagan RJ;Braithwaite RA;Brown SS;Widdop B;de Wolff FA;. The International Programme on Chemical Safety: Basic Analytical Toxicology. WHO, 1995.
^ Peterson, Michael; Talcott, Patricia A. (2006). Small animal toxicology. St. Louis: Saunders Elsevier. pp. 997. ISBN 0-7216-0639-3.
^ See 21 CFR 589.1001
^ A Guide to Glycols (http://www.dow.com/PublishedLiterature/dh_0047/0901b803800479d9.pdf#page=36), page 36.
^ 1,2-Dihydroxypropane SIDS Initial Assessment Profile (http://www.chem.unep.ch/irptc/sids/OECDSIDS/57-55-6.pdf), UNEP Publications, SIAM 11, U.S.A, January 23-26, 2001, page 21.
^ Title 21, U.S. Code of Federal Regulations. 1999.
^ American Medical Association, Council on Drugs (1994). AMA Drug Evaluations Annual 1994 (Chicago, Illinois: American Medical Association): 1224.
^ Elizabeth Vliet MD, Screaming To Be Heard: Hormonal Connections That Women Suspect and Doctors Ignore". M. Evans and Company, Inc. New York 1995
^ "Air Germicide". TIME. Time, Inc.. 1942-11-16. http://www.time.com/time/magazine/article/0,9171,932876,00.html. Retrieved 2009-05-23.

links

http://en.wikipedia.org/wiki/Propylene_glycol#cite_note-0

Chirality