Base-catalyzed reaction in which 1,2-diketone reacts with a hydroxyl ion to give a hydroxyl carboxylate ion, which on acidification yields a hydroxycarboxylic acid. This rearrangement is called benzil-benzilic acid rearrangement. This shows intramolecular disproportionation because the carbon center is oxidized while the other is reduced.

Ketone having no adjacent enolizable proton gives this rearrangement; otherwise, aldol condensation takes place.

Reaction:

Mechanism:

This reaction occurs in four ways, as follows:

Step 1: Nucleophilic addition: 

In this step, base (OH) attacks on one of the carbonyl groups of ketone and nucleophilic addition takes place as follows;

Step(2)

In this step 1,2-phenyl shift takes place.

Step(3):

In this step intramolecular proton shift takes place and stable ion is obtained.

Step(4):

In this step, the carrying oxygen atom abstracts the proton to form α-hydroxyl carboxylic acid derivatives

Application of benzil-benzilic acid rearrangement:

Application of benzil to benzilic acid rearrangement as follows:

• Preparation of feurilic acid from feuril
• synthesis of  α-hydroxy pentane carboxylic acid

Preparation of ferulic acid:

Ferulic acid preparation is the same as the benzilic acid preparation mechanism.

Reaction:

Mechanism:

Synthesis of α-hydroxy pentane carboxylic acid:

Cyclic alkane 1,2-diketone is involved in the ring contraction, e.g. when cyclohexane 1,2-diketone is treated with base give α-hydroxy pentane carboxylic acid as follows:

Reaction:

Mechanism: