March 2007: Propylene Glycol
Propylene glycol (PG) is a colorless, odorless,
viscous (slow-flowing) liquid. It is
hygroscopic (it absorbs moisture from air). It is manufactured from
propylene (C3H6), which is obtained by the thermal cracking of
propane (C3H8).
An alcohol is any organic compound that contains the hydroxyl ( OH) functional group. Glycols are called diols because they contain two hydroxyl groups; and they are described as vicinal because their hydroxyl groups reside on adjacent carbon atoms.
The antifreeze solution used in automobile radiators is often a mixture of PG and water. Any solute that is dissolved in water will lower water’s freezing point. PG is a good choice of solute because it is highly soluble, it does not boil off when the radiator is hot, and it does not promote corrosion. PG also is much less toxic than ethylene glycol, which used to be the most common antifreeze ingredient.
Hydroxyl groups enable glycol molecules to cling to their neighbors by forming hydrogen bonds. These attractions explain why PG is so viscous and also why it has an unusually high boiling point (188°C).
Academics
Site Map