12propanediol

12propanediol, commonly referred to as propylene glycol, is a colorless, viscous liquid with the chemical formula C3H8O2. It is a diol (1,2-propanediol) and has several synonyms, including propylene glycol and E1520 in food regulatory contexts. It is miscible with water and many organic solvents, hygroscopic, and has a boiling point of 188.2 °C and a melting point of −59 °C; its density is about 1.04 g/mL at 20 °C.

Industrial production is dominated by the catalytic hydration of propylene oxide, typically using acidic or basic catalysts to yield predominantly 1,2-propanediol, with smaller amounts of byproducts. Alternative routes from glycerol-derived streams and other feedstocks have been explored, but the hydration of propylene oxide remains the principal method.

Propylene glycol serves a wide range of roles. It is used as a humectant, solvent, and plasticizer in foods, cosmetics, and pharmaceuticals. In the food industry it is employed as a carrier and moisture-retaining agent and is designated as a regulatory food additive (E1520) in many jurisdictions. In cosmetics and topical formulations it functions as a moisturizing vehicle and solvent. It is also used in some pharmaceutical formulations and as an antifreeze or heat-transfer fluid in industrial systems.

Safety and regulation: propylene glycol is regarded as having relatively low acute toxicity and is approved for use in foods, cosmetics, and medicines within specified limits by major regulatory agencies. Exposure in concentrated forms can irritate the eyes and skin, and very high doses may cause metabolic disturbances or central nervous system effects in sensitive individuals. It is considered readily biodegradable and has moderate aquatic toxicity at high concentrations, but overall environmental impact is limited at typical use levels.