Propylene Glycol

propylene glycol, also called propane-1,2-diol or 1,2-propanediol, synthetic organic compound with the chemical formula C₃H₈O₂. Propylene glycol is a colourless liquid that is relatively viscous, has no odour, and tastes slightly sweet. It is hygroscopic, meaning that it readily absorbs water from the surrounding environment. Annual production of propylene glycol in the United States alone exceeds 450 tons. Worldwide demand for propylene glycol is estimated to be approximately 2 million tons annually; demand is expected to grow to nearly 4 million tons by 2035.

Propylene glycol has a molecular weight of 76.09 grams per mole, a boiling point of 187.6 °C (370.8 °F), a melting point of –60 °C (–76 °F), and a density of 1.0361 grams per cubic centimetre at 20 °C (68 °F). It is considered safe for human consumption; however, large doses over short periods of time can be toxic. In a well-sealed container propylene glycol is stable at cooler temperatures. At higher temperatures and in an open container, it oxidizes and produces various chemicals, including lactic acid, pyruvic acid, and acetic acid.

Propylene glycol reacts with strong oxidizing agents, which can result in a fire hazard. As an example, it reacts with hydrofluoric acid (a strong oxidizing agent), nitric acid, and silver nitrate to form silver fulminate, an extremely explosive compound.