diol n : any of a class of alcohols having 2 hydroxyl groups in each molecule [syn: glycol, dihydric alcohol]
A diol or glycol is a chemical compound containing two hydroxyl groups (-OH groups) Vicinal diols have hydroxyl groups attached to adjacent atoms. Examples of vicinal diol compounds are ethylene glycol and propylene glycol. Geminal diols have hydroxyl groups bonded to the same atom. In general, organic geminal diols readily dehydrate to form a carbonyl group. For example, carbonic acid ((HO)2C=O) is unstable and has a tendency to convert to carbon dioxide (CO2) and water (H2O). Nevertheless, in rare situations the chemical equilibrium is in favor of the geminal diol. For example, when formaldehyde (H2C=O) is dissolved in water the geminal diol (H2C(OH)2), methanediol, is favored.
Examples of diols in which the hydroxyl functional groups are more widely separated include 1,4-butanediol and bisphenol A.
Synthesis of diolsBecause diols are a common functional group arrangement, numerous methods of preparation have been developed.
- Vicinal diols can be produced from the oxidation of alkenes, usually with dilute acidic potassium permanganate, also known as potassium manganate(VII). Using alkaline potassium manganate(VII) produces a colour change from clear deep purple to clear green; acidic potassium manganate(VII) turns clear colourless.
- Osmium tetroxide can similarly be used to oxidize alkenes to vicinal diols.
- hydrogen peroxide reacts with an alkene to the epoxide and then by saponification to the diol for example in the synthesis of trans-cyclohexanediol batch or by microreactor :
- A diol reacts like an alcohol, such as esterification and ether formation.
- Diols such as ethylene glycol are used as co-monomers in polymerization reactions forming polymers including some polyesters and polyurethanes. A different monomer with two identical functional groups, such as a dioyl dichloride or dioic acid is required to continue the process of polymerization through repeated esterification processes.
- In glycol cleavage, the C-C bond in a vicinal diol is cleaved with formation of ketone or aldehyde functional groups.
diol in German: Diole
diol in Spanish: Diol
diol in Italian: Dioli
diol in Dutch: Diol
diol in Japanese: グリコール
diol in Polish: Diole
diol in Portuguese: Diol
diol in Russian: Гликоли
diol in Finnish: Dioli
diol in Swedish: Diol
diol in Chinese: 二元醇