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# Benzilic Acid Rearrangement

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 Sub Topics $\alpha$-diketones on treatment with ethanolic potassium hydroxide undergo rearrangement involving 1,2 phenyl shift to give $\alpha$-hydroxy acids. The reaction usually referred to as benzilic acid rearrangement involves the nucleophilic attack of the hydroxide ion at the carbonyl carbon. The intermediate oxyanion then undergoes 1,2-nucleophilic shift of phenyl group to the adjacent carbonyl carbon. The transformation of $\alpha$-diketones to the salts of $\alpha$-hydroxy carboxylic acid, in the presence of bases is known as benzilic acid rearrangement. The best known example is the conversion of benzil into benzilic acid anion.

## Mechanism

The mechanism of benzilic acid rearrangement is an example of 1,2-shift intra molecular rearrangement.

This arrangement involves three steps.
2. Migration of a phenyl group
3. Migration of a proton

The benzilic acid rearrangement is an irreversible process. The first step of the mechanism is the addition of the nucleophile across the C=O bond to give a tetrahedral intermediate.

## Applications

The reaction may be used for the preparation of $\alpha$-hydroxy acids from the easily accessible starting materials.