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Oxidation of Methylene Groups to Carbonyl Groups

Oxidation of Methylene Groups to Carbonyl Groups: Mechanism

A radical mechanism is assumed to be responsible for the oxidation of a methylene group to a carbonyl group. In a chain reaction, the carbon atom adjacent to the phenyl group reacts with biradical oxygen to form a hydroperoxide.

Fig.1

Under homogenous reaction conditions, ions of heavy metal catalysts soluble in the starting material generate radicals from the hydroperoxide, thereby initiating the chain reaction.

Fig.2
Fig.3

Acetophenone and 1-phenylethanol are formed from these readicals.

Fig.4
Fig.5

Subsequently, the alcohol is oxidized to acetophenone in two steps.

Fig.6
Fig.7

The resulting hydrogen peroxide decomposes into water and oxygen which again is available for the reaction.

Fig.8

If the oxidation of ethylbenzene is not stopped at the acetophenone level, further oxidation with cleavage to benzaldehyde and formic acid takes place.

Fig.9
Fig.10

The resulting benzaldehyde subsequently is oxidized to benzoic acid, the endpoint of the ethylbenzenze oxidation.

Fig.11
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