DIOL

A diol is an organic compound containing two hydroxyl groups (-OH). Diols are a subset of polyols and are commonly categorized by the relative positions of the hydroxyl groups: geminal diols have both OH on the same carbon; vicinal diols have OH on adjacent carbons; and other diols are described by the carbon skeleton, such as 1,3- and 1,4-diols.

Geminal diols, such as methanediol, are generally unstable and exist mainly as hydrates of carbonyl compounds rather than isolable substances; vicinal diols are more common and can be prepared by dihydroxylation of alkenes or from acetal chemistry.

Industrial diols are used as solvents, antifreeze agents, or monomers for polyurethanes and polyesters. Ethylene glycol and propylene glycol are notable examples; 1,4-butanediol is a major diol used in polyurethane production and as a precursor to gamma-butyrolactone and other products; 1,3-propanediol is used to make polytrimethylene terephthalate.

Diols tend to form hydrogen bonds, giving higher boiling points than similarly sized hydrocarbons and often higher water solubility. Short-chain diols are typically miscible with water; longer-chain diols may be less soluble but still polar.

Safety considerations vary by compound. Some diols, notably ethylene glycol, are highly toxic if ingested; contact and inhalation hazards require proper handling to avoid irritation or other hazards.