Diol

A diol is an organic chemical compound with two hydroxy groups.^[1] "Di" is a prefix meaning "two", and "ol" comes from "alcohol". An aliphatic diol (one with no aromatic ring) is called a glycol.

Ethylene glycol (also called ethanediol) is the simplest stable diol, and has the chemical formula (CH₂OH)₂.

Types

Geminal diols

If the two hydroxy groups are attached to the same carbon atom, the diol is called geminal. Geminal diols are normally unstable because they easily give up a water molecule to become an aldehyde or ketone.

Vicinal diols

If the two hydroxy groups are on different carbon atoms, but the carbon atoms are attached to each other, the diol is called vicinal. Many vicinal diols are made from epoxides by adding water (hydrolysis).^[2] They can also be made from carbonyls with the pinacol coupling reaction.^[3]

Uses

Diols are important ingredients in plastics like polyester and polyurethane. Important diols in plastic production are 1,4-butanediol, 1,6-hexanediol, and the bisphenols.

Diols can also change carbonyl groups into cyclic acetals. This is used as a protecting group in organic synthesis.^[4]