Propylene glycol

Description

Propylene Glycol is a propanediol that exists as a clear, colorless and hygroscopic liquid. Propylene glycol is used as an organic solvent and diluent in pharmaceuticals and many other industrial applications. It is used as antifreeze in breweries and diaries, in the manufacture of resins, as a solvent, and as an emulsifier in food.

Chemical properties

A colourless, viscous, hygroscopic, low-melting (-59℃) and high-boiling (188℃) liquid with low toxicity, it is used as a solvent, emulsifying agent, and antifreeze.

Occurrence

Reported found in several varieties of mushrooms, roasted sesame seed, oat groats, parmesan cheese, cocoa, pecans and truffle.

Definition

Propane-1,2-diol is the simplest member of the class of propane-1,2-diols, consisting of propane in which a hydrogen at position 1 and a hydrogen at position 2 are substituted by hydroxy groups. A colourless, viscous, hygroscopic, low-melting (-59℃) and high-boiling (188℃) liquid with low toxicity, it is used as a solvent, emulsifying agent, and antifreeze. It has a role as a protic solvent, an allergen, a human xenobiotic metabolite and a mouse metabolite. It is a member of propane-1,2-diols and a glycol.

Preparation

Manufactured by treating propylene with chlorinated water to form the chlorohydrin, which is converted to the glycol by treatment with sodium carbonate solution. It is also prepared by heating glycerol with sodium hydroxide.

Indications

Propylene glycol solution (40% to 60%, v/vCH2CH[OH]CH2OH, propylene glycol) applied to the skin under plastic occlusion hydrates the skin and causes desquamation of scales. Propylene glycol, isotonic in 2% concentration, is a widely used vehicle in dermatologic preparations. Hydroalcoholic gels containing propylene glycol or other substances augment the keratolytic action of salicylic acid. Keralyt gel consists of 6% salicylic acid, 19.4% alcohol, hydroxypropylcellulose, propylene glycol, and water and is an extremely effective keratolytic agent. Overnight occlusion is used nightly until improvement is evident, at which time the frequency of therapy can be decreased to every third night or once weekly. This therapy is well tolerated, is usually nonirritating, and has been most successful in patients with X-linked ichthyosis vulgaris. Burning and stinging may occur when applied to damaged skin. Patients with other abnormalities of keratinization with hyperkeratosis, scaling, and dryness may also benefit.

What are the applications of Application

Propylene glycol is widely used in chemical, pharmaceutical, cosmetic and food fields, and can be used as:
(1) Food additives, in order to help food processing and improve its texture, flavour, appearance and shelf life. It is usually used as anti-caking agent, antioxidant, dough strengthening agent, moisture-proof agent, stabiliser and thickener.
(2) Solvent for injecting drugs.
(3) Used in industry as de-icer, coolant, heat transfer and hydraulic oil, manufacture of smoke, etc.
(4) In cosmetics as low concentration moisturiser, skin conditioner and solvent carrier.

Aroma threshold values

Detection: 340 ppm

Air & Water Reactions

Water soluble.

Reactivity Profile

1,2-Propanediol is hygroscopic. 1,2-Propanediol is sensitive to excessive heat (tends to oxidize at high temperatures). 1,2-Propanediol can react with oxidizing materials. 1,2-Propanediol is incompatible with acid chlorides, acid anhydrides, chloroformates, and reducing agents. 1,2-Propanediol dissolves many essential oils. A mixture of 1,2-Propanediol with hydrofluoric acid and silver nitrate was put in a glass bottle which burst 30 minutes later.

Health Hazard

Liquid may irritate eyes.

Fire Hazard

1,2-Propanediol is combustible.

Toxicity

Slightly toxic by ingestion, skin contact, intraperitoneal, intravenous, subcutaneous, and intramuscular routes. Human systemic effects by ingestion: general anesthesia, convulsions, changes in surface EEG. Experimental teratogenic and reproductive effects. An eye and human skin irritant. Mutation data reported. Combustible liquid when exposed to heat or flame; can react with oxidizing materials. Explosive in the form of vapor when exposed to heat or flame. May react with hydrofluoric acid + nitric acid + silver nitrate to form the explosive silver fulminate. To fight fire, use alcohol foam. When heated to decomposition it emits acrid smoke and irritating fumes.

Potential Exposure

Propylene glycol is used as a solvent; emulsifying agent; food and feed additive; flavor, in manu- facture of plastics; as a plasticizer, surface-active agent; antifreeze, solvent, disinfectant, hydroscopic agent; coolant in refrigeration systems; pharmaceutical, brake fluid; and many others.

Carcinogenicity

Dewhurst et al. and Baldwin et al. in studies on the carcinogenicity of other chemicals used propylene glycol as the solvent. As a result they tested propylene glycol alone for carcinogenic activity in rats and mice. Dewhurst et al. used a single injection of 0.2 mL, whereas Baldwin et al. gave rats and mice three to five subcutaneous injections, amount not specified. In neither case were tumors observed during a period of about a year or 2 years .
Wallenious and Lecholm applied propylene glycol to the skin of rats three times a week for 14 months but found no tumor formation. Stenback and Shubik confirmed these findings when they applied propylene glycol at undiluted strength and as a 50 and 10% solution in acetone to the skin of mice during their lifetimes.
No tumors have been reported in the lifetime dietary feeding studies . In fact, Gaunt et al. specifically state that no tumors were found in the rats.

Safety Profile

Propylene glycol is a common solvent for intravenous drugs, but may be toxic to humans when administered in large doses over a short period of time. Medical overdose of propylene glycol can result in hypertonic and anion gap metabolic acidosis, often associated with acute kidney injury and potential multi-system organ failure, refractory hypotension, cardiac arrhythmias, haemolysis, renal insufficiency, seizures and coma. Paediatric patients may also experience central nervous system depression and seizures.

Environmental Fate

Propylene glycol can be released into the environment via industrial releases or by disposal of consumer products. Propylene glycol is readily soluble in water and has a low sorption partition coefficient (KOC), so has the ability to move through soil and to leach into ground water. Because of low vapor pressure (0.1 mmHg at 25°C) and high water solubility, there is minimal volatilization to the atmosphere from surface water releases as well as substantial removal of its vapors by wet deposition. Its low octanol/water partition coefficient (KOW) indicates that bioconcentration and biomagnification should not happen. Propylene glycol is readily degraded in surface water and soil, by chemical oxidation and microbial digestion, with a short half-life (1–5 days) in aerobic or anaerobic conditions. It is also rapidly degraded in the atmosphere by photochemical oxidation, with a half-life about 1 day. Although environmental releases can and do occur (airports must monitor storm water runoff of deicing solutions), human health effects are likely to be minor, at least in comparison to effects from potential exposures in clinical scenarios.

Toxicity evaluation

Propylene glycol has a low degree of toxicity in animals as well as humans, such that very high doses are needed to elicit effects in acute toxicity studies. The toxic effects of propylene glycol appear to be similar in animals and in humans. Central nervous system (CNS) depression, hematologic toxicity, hyperosmolarity, metabolic acidosis, cardiovascular effects, and renal toxicity encompass the main acute and subacute syndromes for propylene glycol. Most of the effects of propylene glycol can be ascribed to high concentrations of the parent molecule or to the accumulation of D,L-lactate in the blood. Due to its alcohol moiety, propylene glycol at very high concentrations is the most likely reason for the CNS depression. Also, because high concentrations of propylene glycol will increase the osmolarity of the blood, the hyperosmotic effects are likely due to the parent molecule. The cardiovascular and renal effects may be a result of the hyperosmolarity in combination with the metabolic acidosis. The acidosis itself results from the accumulation of lactate (both D- and L-forms), which has been well documented in both animals and humans.

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explo- sions. Keep away from alkaline materials, strong acids (especially nitric acid), strong bases, permanganates, dichromates; may cause a violent reaction.

Waste Disposal

Dissolve or mix the material with a combustible solvent and burn in a chemical incinerator equipped with an afterburner and scrubber.All federal, state, and local environmental regulations must be observed.