Pinacol is a compound which has two hydroxyl groups, each attached to a vicinal carbon atom. It is a solid organic compound which is white in colour. The IUPAC name of Pinacolone is 3,3-dimethyl-2-butanone. Pinacolone is a very important ketone.
Pinacol and Pinacolone
Pinacol is a compound which has two hydroxyl groups, each attached to a vicinal carbon atom. It is a solid organic compound which is white in colour.
The IUPAC name of Pinacolone is 3,3-dimethyl-2-butanone. Pinacolone is a very important ketone. It has a peppermint like or camphor like odour and appears to be a colorless liquid.
Pinacol Pinacolone Reaction
The pinacol pinacolone rearrangement proceeds through the formation of an intermediate which is positively charged. The methyl group in this intermediate proceeds to migrate from one carbon to another. This reaction can be given by:
Pinacol Pinacolone Rearrangement Mechanism
The Pinacol Pinacolone rearrangement mechanism proceeds via four steps. Each of these steps are explained below.
Step 1: Since the reaction is carried out in an acidic medium, the hydroxide group of the pinacol is protonated by the acid.
Step 2: Water is now removed from the compound, leaving behind a carbocation. This carbocation is tertiary and therefore stable.
Step 3: The methyl group shifts to the positively charged carbon in a rearrangement of the compound.
Step 4: The oxygen atom which is doubly bonded to the carbon is now deprotonated, giving rise to the required pinacolone.
This reaction mechanism can be illustrated as:
Thus, the required Pinacolone product is generated. It is important to note that this rearrangement is regioselective in nature. The rearrangement of the more stable carbocation yields the major product.
Pinacol-Pinacolone Rearrangement
Pinacol-Pinacolone Rearrangement
A 1,2-methyl shift generates an even more stable carbocation in which the charge is delocalized by heteroatom resonance. Indeed, this new cation is simply the conjugate acid of the ketone pinacolone, which is the product of repeated rearrangements catalyzed by proton transfer.
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