Ch17: Baeyer-Villiger reaction

Chapter 17: Aldehydes and Ketones. Nucleophilic Addition to C=O

The Baeyer-Villiger Reaction

Baeyer-Villager of an ketone

Baeyer-Villager for an aldehyde

Reaction type: Oxidation-reduction via Nucleophilic addition

Summary

Ketones, RCOR', are oxidised by peracids (or hydrogen peroxide) to give esters, RCO₂R'.
Aldehydes, RCHO, are oxidised under the same conditions to give carboxylic acids, RCO₂H.
For ketones, it can be viewed as the insertion of O into one of the C-C bonds adjacent to the carbonyl group.
For non-symmetrical systems, there is a selectivity issue. Experimental evidence shows that it is usually the more highly substituted alkyl group that migrates and becomes attached to the inserted O atom. : i.e. (more likely) H > 3^o R > 2^o R > Ar > 1^o R > -CH₃ (less likely)
This is described as the "migratory aptitude" of the group and it relates to the ability of the group to stablise +ve charge (i.e. the more nucleophilic group tends to migrate).

In this example, the ethyl group (primary C) migrates in preference to the methyl group, so we end up with an ethyl ester.

lactone

unsymmetrical cyclic example

In this example the "O" inserts on the more substituted side.

Study Tip:
It's easy to make an avoidable mistake here, especially with the cyclic systems and loose a C atom.

Count C atoms!

In the example above, the 5-membered ring becomes a 6-membered ring because an O atom has been added to the cyclic system.

Related Reactions

THE BAEYER-VILLIGER REACTION
Step 1: An acid/base reaction. Protonation of the carbonyl activates it while creating a more reactive nucleophile, the percarboxylate.
Step 2: Now the nucleophilic O attacks the carbonyl C with the electrons from the C=O π bond going to the positive O.
Step 3: Electrons from the O come back (this reforms the π bond of the C=O) and we migrate the C-C electrons to form a new C-O bond displacing the carboxylate as a leaving group.
Step 4: Finally an acid/base reaction reveals the C=O and therefore the ester product.