Propylene glycol
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Names | |||
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Preferred IUPAC name
Propane-1,2-diol | |||
Other names
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Identifiers | |||
3D model (
JSmol ) |
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ChEBI | |||
ChEMBL | |||
ChemSpider | |||
ECHA InfoCard
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100.000.307 | ||
EC Number |
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E number | E1520 (additional chemicals) | ||
KEGG | |||
PubChem CID
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RTECS number
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UNII |
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CompTox Dashboard (EPA)
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Properties | |||
C3H8O2 | |||
Molar mass | 76.095 g·mol−1 | ||
Appearance | colourless liquid | ||
Odor | odorless | ||
Density | 1.036 g/cm3 | ||
Melting point | −59 °C (−74 °F; 214 K) | ||
Boiling point | 188.2 °C (370.8 °F; 461.3 K) | ||
Miscible
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Solubility in ethanol | Miscible | ||
Solubility in diethyl ether | Miscible | ||
Solubility in acetone | Miscible | ||
Solubility in chloroform | Miscible | ||
log P | -1.34[2] | ||
Thermal conductivity
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0.34 W/m-K (50% H2O @ 90 °C (194 °F)) | ||
Viscosity | 0.042 Pa·s | ||
Pharmacology | |||
QA16QA01 (WHO) | |||
Hazards | |||
NFPA 704 (fire diamond) | |||
Related compounds | |||
Related
glycols |
1,3-propanediol
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Propylene glycol (
It is produced on a large scale primarily for the production of
Structure
The compound is sometimes called (alpha) α-propylene glycol to distinguish it from the
Production
Industrial
Industrially, propylene glycol is mainly produced from propylene oxide (for food-grade use). According to a 2018 source, 2.16 M tonnes are produced annually.[6] 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.[7]
Final products contain 20% propylene glycol, 1.5% of dipropylene glycol, and small amounts of other polypropylene glycols.[8] Further purification produces finished industrial grade or USP/JP/EP/BP grade propylene glycol that is typically 99.5% or greater. Use of USP (US Pharmacopoeia) propylene glycol can reduce the risk of Abbreviated New Drug Application (ANDA) rejection.[9]
Propylene glycol can also be obtained from glycerol, a byproduct from the production of biodiesel.[6] This starting material is usually reserved for industrial use because of the noticeable odor and taste that accompanies the final product.
Laboratory
(S)-Propanediol is synthesized via fermentation methods.
A small-scale, nonbiological route from D-mannitol is illustrated in the following scheme:[10]
Applications
Polymers
Forty-five percent of propylene glycol produced is used as a chemical feedstock for the production of unsaturated
Food and drug
Propylene glycol is also used in various edible items such as coffee-based drinks,
Antifreeze
The
Electronic cigarettes liquid
Propylene glycol, vegetable
Miscellaneous applications
- As a solvent for many substances, both natural and synthetic.[23]
- As a humectant (E1520).
- As a freezing point depressant for slurry ice.
- In veterinary medicine as an oral treatment for
- In the cosmetics industry, where propylene glycol is very commonly used as a carrier or base for various types of makeup.[25]
- For trapping and preserving insects (including as a DNA preservative).[26]
- For the creation of theatrical smoke and fog in special effects for film and live entertainment. So-called 'smoke machines' or 'hazers' vaporize a mixture of propylene glycol and water to create the illusion of smoke. While many of these machines use a propylene glycol-based fluid, some use oil. Those which use propylene glycol do so in a process that is identical to how electronic cigarettes work; utilizing a heating element to produce a dense vapor. The vapor produced by these machines has the aesthetic look and appeal of smoke, but without exposing performers and stage crew to the harms and odors associated with actual smoke.[27][28]
- As an additive in GC rich sequences.[citation needed]
- As a surfactant, it is used to prevent water from beading up on objects. It is used in photography for this purpose to reduce the risk of water spots, or deposits of minerals from water used to process film or paper.
Safety in humans
When used in average quantities, propylene glycol has no measurable effect on development and/or reproduction on animals and probably does not adversely affect human development or reproduction without active use.
Oral administration
The acute oral toxicity of propylene glycol is very low, and large quantities are required to cause perceptible health effects in humans; in fact, the toxicity of propylene glycol is one third of ethanol's.[34] Propylene glycol is metabolized in the human body into pyruvic acid (a normal part of the glucose-metabolism process, readily converted to energy), acetic acid (handled by ethanol-metabolism), lactic acid (a normal acid generally abundant during digestion),[35] and propionaldehyde (a potentially hazardous substance).[36][37][38] According to the Dow Chemical Company, the LD50 (dose that kills 50% of the test population) for rats is 20 g/kg (oral/rat).[39][40]
Toxicity generally occurs at plasma concentrations over 4 g/L, which requires extremely high intake over a relatively short period of time, or when used as a vehicle for drugs or vitamins given intravenously or orally in large
The potential for long-term oral toxicity is also low. In a National Toxicology Program continuous breeding study, no effects on fertility were observed in male or female mice that received propylene glycol in drinking water at doses up to 10100 mg/kg bw/day. No effects on fertility were seen in either the first or second generation of treated mice.[29] In a 2-year study, 12 rats were provided with feed containing as much as 5% propylene glycol, and showed no apparent ill effects.[44] Because of its low chronic oral toxicity, propylene glycol was classified by the U. S. Food and Drug Administration as "generally recognized as safe" (GRAS) for use as a direct food additive, including frozen foods such as ice cream and frozen desserts.[42][45] The GRAS designation is specific to its use in food, and does not apply to other uses.[46]
Skin and eye contact
Propylene glycol may be non-irritating to the skin, see section Allergic reaction below for details on allergic reactions.[47] Undiluted propylene glycol is minimally irritating to the eye, producing slight transient conjunctivitis; the eye recovers after the exposure is removed.
A 2018 human volunteer study found that 10 male and female subjects undergoing 4 hours exposures to concentrations of up to 442 mg/m3 and 30 minutes exposures to concentrations of up to 871 mg/m3 in combination with moderate exercise did not show pulmonary function deficits, or signs of ocular irritation, with only slight symptoms of respiratory irritation reported.[48]
Propylene glycol has not caused sensitization or carcinogenicity in laboratory animal studies, nor has it demonstrated genotoxic potential.[49][50]
Inhalation
Inhalation of propylene glycol vapors appears to present no significant hazard in ordinary applications.
According to a 2010 study, the concentrations of PGEs (counted as the sum of propylene glycol and
Intravenous administration
Studies with intravenously administered propylene glycol have resulted in LD50 values in rats and rabbits of 7 mL/kg BW. However, no confirmed lethality from propylene glycol was reported.
Animals
Propylene glycol is an approved food additive for dog and sugar glider food under the category of animal feed and is generally recognized as safe for dogs,[62] with an LD50 of 9 mL/kg. The LD50 is higher for most laboratory animals (20 mL/kg).[63] However, it is prohibited for use in food for cats due to links to Heinz body formation and a reduced lifespan of red blood cells.[64] Heinz body formation from MPG has not been observed in dogs, cattle, or humans.
PG has been used in the
Allergic reaction
Estimates on the prevalence of propylene glycol allergy range from 0.8% (10% propylene glycol in aqueous solution) to 3.5% (30% propylene glycol in aqueous solution).[66][67][68] The North American Contact Dermatitis Group (NACDG) data from 1996 to 2006 showed that the most common site for propylene glycol contact dermatitis was the face (25.9%), followed by a generalized or scattered pattern (23.7%).[66] Investigators believe that the incidence of allergic contact dermatitis to propylene glycol may be greater than 2% in patients with eczema or fungal infections, which are very common in countries with lesser sun exposure and lower-than-normal vitamin D balances. Therefore, propylene glycol allergy is more common in those countries.[69]
Because of its potential for allergic reactions and frequent use across a variety of topical and systemic products, propylene glycol was named the American Contact Dermatitis Society's Allergen of the Year for 2018.[70][71] Recent publication from The Mayo Clinic reported 0.85% incidence of positive patch tests to propylene glycol (100/11,738 patients) with an overall irritant rate of 0.35% (41/11,738 patients) during a 20-year period of 1997–2016.[72] 87% of the reactions were classified as weak and 9% as strong. The positive reaction rates were 0%, 0.26%, and 1.86% for 5%, 10%, and 20% propylene glycol respectively, increasing with each concentration increase. The irritant reaction rates were 0.95%, 0.24%, and 0.5% for 5%, 10%, and 20% propylene glycol, respectively. Propylene glycol skin sensitization occurred in patients sensitive to a number of other concomitant positive allergens, most common of which were: Myroxylon pereirae resin, benzalkonium chloride, carba mix, potassium dichromate, neomycin sulfate; for positive propylene glycol reactions, the overall median of 5 and mean of 5.6 concomitant positive allergens was reported.
Environmental impacts
Propylene glycol occurs naturally, probably as the result of anaerobic catabolism of sugars in the human gut. It is degraded by vitamin B12-dependent enzymes, which convert it to propionaldehyde.[73]
Propylene glycol is expected to degrade rapidly in water from biological processes, but is not expected to be significantly influenced by hydrolysis, oxidation,
Propylene glycol is readily biodegradable under aerobic conditions in freshwater, in seawater and in soil. Therefore, propylene glycol is considered as not persistent in the environment.Propylene glycol exhibits a low degree of toxicity toward aquatic organisms. Several guideline studies available for freshwater fish with the lowest observed lethal concentration of 96-h
Although propylene glycol has low toxicity, it exerts high levels of
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External links
- Agency for Toxic Substances and Disease Registry
- Alton E. Martin - Frank H. Murphy, DOW CHEMICAL COMPANY
- Propylene glycol website
- WebBook page for C3H8O2
- ATSDR - Case Studies in Environmental Medicine: Ethylene Glycol and Propylene Glycol Toxicity U.S. Department of Health and Human Services(public domain)
- Propylene Glycol - chemical product info: properties, production, applications.
- ChemSub Online: Propylene glycol
- Propylene Glycol Toxicity in Pets