1.5.4 Oxidation of Thioethers
The thioethers could be oxidized to the corresponding sulfoxides and sulfones using peracids (Scheme 10).
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Scheme 10 |
1.5.5 Oxidation of Ketones (Baeyer-Villiger Oxidation)
Ketones undergo reaction with peracids to give esters by insertion of oxygen (Scheme 11). The reaction is known as Baeyer-Villiger oxidation.
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Scheme 11 |
Mechanism
The first step involves protonation of carbonyl oxygen (Scheme 12). The addition of peracid to the protonated carbonyl group gives a tetrahedral intermediate. Elimination of the carboxylate anion and migration of R to the electron deficient oxygen atom occur simultaneously. The resulting protonated form of the ester loses a proton to yield ester. It is believed that the loss of carboxylate anion and migration of R are concerted. The labeling study with O18 suggests that the carbonyl oxygen of the ketones becomes the carbonyl oxygen of the ester.
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Scheme 12 |
Migratory Aptitude
Aryl groups migrate in preference to methyl and primary alkyl groups. The order of preference for the migration of alkyl groups is 3◦ > 2◦ > 1◦ > methyl. The order of preference for the migration of aryl groups is p-OMeC6H4 > C6H5 > p-NO2C6H4 (Scheme 13).
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Scheme 13 |