glycol

glycol (glī'kōl), dihydric alcohol in which the two hydroxyl groups are bonded to different carbon atoms; the general formula for a glycol is (CH₂)_n(OH)₂. The most important glycol is the simplest, ethylene glycol, or 1,2-ethanediol, CH₂OHCH₂OH, a slightly sweet-tasting, somewhat viscous liquid that is miscible with water. Because of its low volatility (b.p. 197°C) and low corrosive activity, it is widely used in mixtures of automobile antifreeze. Ethylene glycol can be esterified to form polyesters, e.g., Dacron, and can be nitrated to form an explosive used in mining. It is prepared commercially by oxidation of ethylene at high temperature over a silver oxide catalyst, followed by acid-catalyzed hydrolysis of the ethylene oxide that is formed.

Cellosolves (e.g., methyl cellosolve, CH₃OCH₂CH₂OH) are monoether derivatives of ethylene glycol. They are excellent solvents, having solvent properties of both ethers and alcohols; they have other uses as well. Polyethylene glycol (PEG) is used to thicken shampoo and cosmetics. It can also be attached to other molecules via a process called pegylation. When pegylated to medicinal drugs, it can alter their distribution in the body, metabolism, and excretion. Such alteration can lead to improved dosing intervals and may also have beneficial effects on safety and efficacy. Pegylation can also mask certain drugs, such as interferon, from the immune system, preventing their rejection.