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{{chembox
verifiedrevid = 265988423
Reference =
Name = Propylene glycol
ImageFile = Propylene glycol chemical structure.png
ImageSize = 200px
ImageName = Propylene glycol
ImageFileR1 = PropyleneGlycol-spaceFill.png
ImageSizeR1 = 100px
ImageNameR1 = Space-filling model
ImageFileL1 = PropyleneGlycol-stickAndBall.png
ImageSizeL1 = 100px
ImageNameL1 = ball-and-stick model
IUPACName = propane-1,2-diol
OtherNames = propylene glycol, α-propylene glycol, 1,2-propanediol, 1,2-Dihydroxypropane, methyl ethyl glycol (MEG), methylethylene glycol, PG, Sirlene, Dowfrost
Section1 =
Section2 = {{Chembox Properties
Formula = C3H8O2
MolarMass = 76.09 g/mol
Density = 1.036 g/cm³
MeltingPt = -59 °C
Solubility = fully miscible
Solubility1 = fully miscible
Solvent1 = ethanol
Solubility2 = fully miscible
Solvent2 = diethyl ether
Solubility3 = fully miscible
Solvent3 = acetone
Solubility4 = fully miscible
Solvent4 = chloroform
BoilingPt = 188.2 °C
ThermalConductivity = W/m-K (50% H2O @ 90°C)
 }}
Section7 =
Section8 =}}

Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound (a diol or double alcohol) with formula C3H8O2 or HO-CH2-CHOH-CH3. It is a colorless, nearly odorless, clear, viscous liquid with a faintly sweet taste, and is a that is hygroscopic and miscible with water, acetone, and chloroform.

The compound is sometimes called α-propylene glycol to distinguish it from the isomer propane-1,3-diol HO-(CH2)3-OH, also called β-propylene gycol.

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.

Production

Industrially propylene glycol is produced by propylene oxide . Different manufacturers use either non-catalytic high-temperature process at to , or a catalytic method, which proceeds at to 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. Propylene glycol can also be converted from glycerol, a biodiesel byproduct.

Applications

Propylene glycol is used:

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.

Properties

Propylene glycol is a component in newer automotive antifreezes and de-icers used at airports. Like ethylene glycol, the freezing point of propylene glycol is depressed when mixed with water due to disruption of hydrogen bonding. Unlike ethylene glycol, propylene glycol is much lower in toxicity. Both are readily biodegradable.



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, especially in combination with alcohol or MDMA 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. 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.

Serious toxicity will occur only at plasma concentrations over 4g/L, which requires extremely high intake over a relatively short period of time. 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 (LD50at levels of 20mL/kg). 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.

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.

Propylene glycol does not cause sensitization and it shows no evidence of being a carcinogen or of being genotoxic.

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 phenytointhat contained PG as a solvent. Their symptoms resolved when they were switched to a phenytoin formulation without PG.

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.

Patients with vulvodyniaand interstitial cystitismay be especially sensitive to propylene glycol. Women struggling with yeast infections may also notice that some OTC creams can cause intense burning. 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 pharmacymake a "propylene glycol free" cream.

Possible air germicide

Studies conducted in 1942 by Dr. Oswald Hope Robertson of University of Chicagomarker'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. After a few months of treatment, no ill effects were discovered.

See also



References

  1. Merck Index, 11th Edition, 7868.
  2. 1,2-propanediol: chemical product info at CHEMINDUSTRY.RU
  3. "
  4. http://pubs.acs.org/cen/whatstuff/stuff/7901scit5.html
  5. 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.
  6. 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.
  7. Flanagan RJ;Braithwaite RA;Brown SS;Widdop B;de Wolff FA;. The International Programme on Chemical Safety: Basic Analytical Toxicology. WHO, 1995.
  8. See 21 CFR 589.1001
  9. A Guide to Glycols (http://www.dow.com/PublishedLiterature/dh_0047/0901b803800479d9.pdf#page=36), page 36.
  10. 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.
  11. Title 21, U.S. Code of Federal Regulations. 1999.
  12. Elizabeth Vliet MD, Screaming To Be Heard: Hormonal Connections That Women Suspect and Doctors Ignore". M. Evans and Company, Inc. New York 1995


External links



Freezing Points of Propylene Glycol - Water Mixtures
Percent Propylene Glycol (wt. %)
Freezing Point (°F)
Freezing Point (°C)
0
32
0
10
26
-3
20
20
-7
30
10
-12
36
0
-18
40
-5
-20
43
-10
-23
48
-20
-29
52
-30
-34
55
-40
-40
58
-50
-46
60
-60
-51

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