Mechanistic Study of Carboxylate Ion Reactivity and Keto-Enol Tautomerization in ?-Keto Acid Formation

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Mechanistic Study of Carboxylate Ion Reactivity and Keto - Enol Tautomerization in α - Keto Acid Formation Solution: At first the carboxylate ion (as reaction condition is acidic) will accept a proton and will change into corresponding carboxylic acid. In the next step the hemiacetal oxygen will attack a proton through its electron lone pair and in the process gets protonated. Now electron pair of water molecule attacks the carbon α to the carboxylic acid group and simultaneously the C - O σ bond will get broken (to maintain the carbon tetravalency) and its bonding electrons moves to the positively charged oxygen atom. In the next step keto - enol tautomerization will take place. During this process the ketone is more stable and thus the equilibrium will shift more towards the ketone product (that is at equilibrium amount of ketone will be more). Now the water molecule will get eliminated (along with the C - O bonding electron pair) from the intermediate obtained in the last step. Simultaneously the electron lone pair of the hydroxyl group will move in (to maintain carbon tetravalency) to form a π - bond . This will result into formation of another carbonyl group with protonated oxygen. Finally the proton is attacked by the electron lone pair of water molecule and simultaneously the σ - bond electron will move on the positively charged oxygen resulting in the formation of diketone molecule.
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