Propylene glycol (IUPAC name: propane-1,2-diol ) is a synthetic organic compound with the chemical formula C 3 H 8 O 2 . It is a thick, colorless liquid that is virtually odorless but has a slightly sweet taste. It is chemically classified as a diol and can be mixed with various solvents, including water, acetone, and chloroform.
It is manufactured on a large scale and is mainly used in the production of polymers, but also sees used in food processing, and as a process liquid in low temperature heat exchange applications. In the EU, it has E-number E1520 for food applications. For cosmetics and pharmacology, the number is E490.
This compound is sometimes called (alpha) ? - propylene glycol to distinguish it from the propane-1,3-diol isomer, known as (beta)? -propylene glycol.
Video Propylene glycol
Structure and properties
Propylene glycol is a clear, colorless and hygroscopic liquid. Propylene glycol contains asymmetric carbon atoms, so it exists in two enantiomers. Commercial products are a mixture of racemates. Pure optical isomers can be obtained by pure propylene oxide hydration.
The freezing point of water is suppressed when mixed with propylene glycol, due to the dissolving effect of the solute in the solvent (freezing point of depression). Generally, glycol is not corrosive, has very low volatility and very low toxicity; however, the closely related ethylene glycol (the main ingredient in antifreeze) is toxic to humans and many animals.
Maps Propylene glycol
Production
Industrial
Industrially, propylene glycol is produced from propylene oxide (for the use of food grade), and the global capacity in 1990 is 900,000 tons per year. Different manufacturers use a non-catalytic high temperature process at 200 ° C (392 ° F) to 220 ° C (428 ° F), or catalytic method, which takes place at 150 ° C (302 ° C). F) up to 180 ° C (356 ° F) in the presence of ion exchange resins or small amounts of sulfuric or alkaline acids.
The final product contains 20% propylene glycol, 1.5% of dipropylene glycol and a small amount of other polypropylene glycols. Further purification produces an industrial grade or USP/JP/EP/BP propylene glycol grade which is usually 99.5% or greater. Propylene glycol can also be converted from glycerol, a by-product of biodiesel. These starting materials are usually provided for industrial use because of the striking smells and flavors that accompany the final product.
Laboratory
S - Propanediol can be synthesized from D -mannitol, through the following scheme:
Apps
Forty-five percent of the propylene glycol produced is used as a chemical feedstock for the production of unsaturated polyester resins. In this case, propylene glycol reacts with an unsaturated mixture of maleic anhydride and isophthalic acid to produce copolymers. This partially unsaturated polymer undergoes further crosslinking to produce thermoset plastics. Associated with this application, propylene glycol reacts with propylene oxide to produce oligomers and polymers used to produce polyurethane. Propylene glycol is used as a humectant (E1520), solvent, and preservative in food and for tobacco products. It is also one of the main ingredients (& lt; 1-92%), along with glycerol, from e-liquids and cartridges used in electronic cigarettes where it aerosols in a sprayer. Propylene glycol is also used in various edible foods such as coffee-based beverages, liquid sweeteners, ice cream, shake milk products and soda. Vaporizers used for the delivery of drugs or personal care products often include propylene glycol among ingredients. In an alcohol-based hand sanitizer, it is used as a humectant to prevent dry skin. Propylene glycol is used as a solvent in many drugs, including oral, injectable and topical formulations, such as for diazepam and lorazepam that are insoluble in water. Certain formulations of artificial tears, such as Systane, use proplyen glycol as the ingredient.
Like ethylene glycol, propylene glycol is capable of lowering the freezing point of water, and is therefore used as a de-icing fluid for aircraft. The propylene glycol mixture of pink dyed water to show a relatively non-toxic mixture is sold under the name RV or sea antifreeze. Propylene glycol is often used as a substitute for ethylene glycol in low toxicity, environmentally friendly automotive antifreeze. It is also used to freeze piped systems in empty structures. The eutectic composition/temperature is 60:40 propylene glycol: water/-60 Â ° C. However, the commercial product -50 Â ° F/-45 Â ° C is water-rich; Typical formulation is 40:60.
Propylene glycol is used in the treatment of animals as an oral treatment for hyperkalemi in ruminant animals. Glucose, which can be used in non-ruminants for this purpose, is ineffective because of the consumption by the resident microbes from the rumen. Propylene glycol is partially metabolized in rumen to propionate which can be used as an energy source. The rest is absorbed into the bloodstream and used by the liver for gluconeogenesis.
Safety in humans
Oral administration
Acute oral toxicity of propylene glycol is very low, and large quantities are required to cause significant human health damage; propylene glycol is metabolized in the human body into pyruvic acid (the normal part of the glucose metabolism process, readily converted to energy), acetic acid (handled by ethanol-metabolism), lactic acid (normal acid which is generally abundant during digestion), and propionaldehyde potentially dangerous). According to Dow Chemical Company, LD 50 (Dose Lethal that kills in 50% test,) for mice is 20 g/kg (rat/oral).
Serious toxicity generally occurs in plasma concentrations greater than 4 g/L, which require a very high intake over a relatively short period of time, or when used as a vehicle for drugs or vitamins administered intravenously or orally. It is almost impossible to reach toxicity by consuming foods or supplements, containing at most 1 g/kg of PG, except for US 5% = 50g/kg. The case of propylene glycol poisoning is usually associated with improper intravenous administration or inadvertently swallowing large amounts by children.
The potential for long-term oral toxicity is also low. In one study, in 1972, 12 mice were fed a feed containing as much as 5% PG over a 2 year period, and showed no real pain effects; no data on the offspring offered. Due to low chronic oral toxicity, propylene glycol is classified by the US 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. The GRAS stipulation is specific to its use in food, and does not apply to other uses.
Skin contact, eye and inhalation
Prolonged contact with propylene glycol (E490) essentially does not cause irritation to the skin. Undiluted propylene glycol minimally irritates the eye, resulting in minimal transient conjunctivitis; eyes recover after exposure is removed. Exposure to mist can cause eye irritation, as well as upper respiratory tract irritation. Inhalation of propylene glycol vapors does not appear to pose a significant hazard in regular applications. However, limited human experience suggests that inhalation of propylene glycol fog may disrupt some individuals. It is therefore recommended that propylene glycol is not used in applications where exposure to inhalation or human eye contact with spray mist of these materials is likely, such as simulated fog for theatrical production, or antifreeze solutions for emergency eye wash stations.
According to a 2010 study by Karlstad University, the concentrations of PGEs (calculated as the amount of propylene glycol and glycol ether) in indoor air, particularly bedroom air, have been associated with an increased risk of developing various respiratory and immune disorders in children, including asthma, fever, eczema, and allergies, with an increased risk ranging from 50% to 180%. This concentration has been linked to the use of water-based paints and water-based cleaning systems. However, the study authors wrote that glycol ether and not propylene glycol were the possible causes.
Propylene glycol does not cause sensitization, and does not indicate carcinogen or genotoxicity.
Intravenous Administration
The adverse response to intravenous administration of propylene glycol as excipients has been seen in a number of people, especially with large doses. The response may include "hypotension, bradycardia... QRS and T abnormalities in ECG, arrhythmia, cardiac arrest, serum hyperosmolality, lactic acidosis, and haemolysis". A high percentage (12% to 42%) of the injected propylene glycol is directly eliminated or secreted in urine unchanged depending on the dose, with the remainder appearing in its glucuronide form. The speed of renal filtration decreases with increasing dosage, which may be caused by mild anesthetic propylene glycol/CNS-depressant-properties as alcohol. In one case, intravenous administration of propylene glycol-suspended nitroglycerin to an elderly man may have led to coma and acidosis.
Animal
Propylene glycol is a food additive approved for dog food and glider sugar under the animal feed category and is generally recognized as safe for dogs, with LD 50 of 9 mL/kg. LD 50 is higher for most laboratory animals (20 mL/kg). However, it is forbidden to use in food for cats because of its relation to Heinz body anemia.
Allergic reaction
Individuals who can not tolerate the propylene glycol experience inflamed dry skin in the face area, or small red dots in the body. Researchers believe that the incidence of allergic contact dermatitis to propylene glycol may be greater than 2% in patients with eczema or fungal infections, which is very common in countries with lower sun exposure, and lower than normal vitamin D balance. Therefore, propylene glycol allergies are more common in these countries.
Environment
Propylene glycol is known to exert a high level of biochemical oxygen demand (BOD) during degradation at the water surface. This process can affect aquatic life by consuming the oxygen needed by aquatic organisms to survive. A large amount of dissolved oxygen (DO) in the water column is consumed when the microbial population decomposes propylene glycol.
Sufficient levels of dissolved oxygen on the surface of the water are essential for the survival of fish, macroinvertebrates, and other aquatic organisms. If the concentration of oxygen falls below the minimum level, the organism emigrates, if able and possible, to areas with higher oxygen levels or eventually dies. This effect can drastically reduce the amount of aquatic habitats that can be used. DO level reductions can reduce or eliminate bottom feeder populations, create conditions that support changes in the profile of community species, or alter critical food-web interactions.
References
External links
- The propylene glycol website
- WebBook page for C3H8O2
- ATSDR - Case Study in Environmental Medicine: Ethylene Glycol and Propylene Glycol Toxicity Department of Health and Human Services US (public domain)
- Propylene Glycol - chemical product info: property, production, application.
- ChemSub Online: Propylene glycol
Source of the article : Wikipedia
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