Base catalyzed reaction in which 1,2-diketone reacts with 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:
