Propylene glycol is a clear, colorless and hygroscopic liquid. Propylene glycol contains an asymmetrical carbon atom, so it exists in two stereoisomers. The freezing point of water is depressed when mixed with propylene glycol due to increased opportunity for hydrogen bonding.
Applications
Propylene glycol is a solvent in many pharmaceuticals, including oral, injectable and topical formulations, such as for diazepam and lorazepam that are insoluble in water, use propylene glycol as a solvent in their clinical, injectable forms. It is also used as automotive antifreeze.