Diol

A diol or '''glycol''' is a Chemical Compound containing two Hydroxyl Group s (-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) is favored.

Examples of diols in which the hydroxyl functional groups are more widely separated include 1,4-butanediol and Bisphenol A .

SYNTHESIS OF DIOLS

Because diols are a common functional group arrangement, numerous methods of preparation have been developed.

Vicinal diols can be produced from the Oxidation of Alkene s, 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.

A chemical reaction called Sharpless Bishydroxylation can be used to produce 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 .

REACTIONS

A diol reacts like an Alcohol , such as Esterification and Ether formation.

Diols such as Ethylene Glycol are used as co- Monomer s in Polymerization reactions forming Polymer s including some Polyester s and Polyurethane s. 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 two aldehyde groups.

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Diol