Glycol

A glycol is an aliphatic organic compound in which two hydroxyl (OH) groups are present. The most important glycols are those in which the hydroxyl groups are attached to adjacent carbon atoms, and the term glycol is often interpreted as applying only to such compounds. The latter are also called vicinal diols, or 1,2-diols. Compounds in which two hydroxyl groups are attached to the same carbon atom (geminal diols) normally cannot be isolated.

The most useful glycol is ethylene glycol (IUPAC name: 1,2-ethanediol). Other industrially important glycols include propylene glycol (IUPAC name: 1,2-propanediol), diethylene glycol (IUPAC name: 3-oxa-1,5-pentanediol) and tetramethylene glycol (IUPAC name: 1,4-butanediol)(Figure 1).

The most convenient and inexpensive method of preparing a glycol in the laboratory is to react an alkene with cold dilute potassium permanganate, KMnO₄ (Figure 2).

Yields from this reaction are often poor and better yields are obtained using osmium tetroxide, OsO₄. However, this reagent has the disadvantages of being expensive and toxic.

Figure 4. Synthesis of poly(ethylene terephthalate). Illustration by Hans & Cassidy. Courtesy of Gale Group.