Diol
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(Redirected from Glycols)
A diol is a chemical compound containing two hydroxyl groups (-OH groups).
- Vicinal diols have hydroxyl groups bonded to atoms next to each other, i. e. bonded to each other. Examples of vicinal diol compounds are ethylene glycol and propylene glycol.
- Geminal diols have hydroxyl groups bonded to the same atom.
When the atom is a carbon atom in an organic compound, the diol section of the molecule is unstable and has a tendency to dehydrate forming a carbonyl group. For example, carbonic acid (HO-CO-OH) is unstable and has a tendency to convert to carbon dioxide (CO2) and water (H2O). Only when formaldehyde (H-CO-H) is dissolved in water is the chemical equilibrium in favor of the geminal diol version of the compound [H-C(OH)2-H].
Other examples of diols are 1,4-Butanediol and Bisphenol A.
[edit] Synthesis of diols
- 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 diols.
- A chemical reaction called Sharpless bishydroxylation can be used to yield chiral diols from alkenes using an osmate reagent and a chiral catalyst.
- Another method is the Woodward cis-hydroxylation.
- In the Prins reaction 1,3-diols can be formed in a reaction between an alkene and formaldehyde.
[edit] Reactions
- A diol reacts like an alcohol for instance in esterfications en ether formation.
- Diols such as ethylene glycol are used as co-monomers in some polymerization reactions forming polymers such as certain polyesters and polyurethanes.
- In glycol cleavage the C-C bond in a vicinal diol is cleaved with formation of two aldehyde groups.
