Dakin rearrangement

This list has to be continued by the Dakin rearrangement, which is the oxidation of aromatic ortho- or para-hydroxyaldehydes with H2O2 in the presence of alkali to afford polyhydric phenols (equation 133). 

Dakin oxidation 419, 420 Dakin rearrangement 799, 800 Dehalogenation 1098-1100 Dehydrodiconiferyl alcohol, mass spectrum of... 

The Dakin reaction proceeds by a mechanism analogous to that of the Baeyer-Villiger reaction. An aromatic aldehyde or ketone that is activated by a hydroxy group in the ortho or para position, e.g. salicylic aldehyde 12 (2-hydroxybenzaldehyde), reacts with hydroperoxides or alkaline hydrogen peroxide. Upon hydrolysis of the rearrangement product 13 a dihydroxybenzene, e.g. catechol 14, is obtained ... 

There are a number of less frequently used methods for the preparation of phenols that are worthy of mention. The rearrangement of 2-hydroxy-benzaldehydes brought about by reaction with alkaline hydrogen peroxide and leading to dihydroxybenzenes (the Dakin reaction ) is discussed in Section 4.8. The acid-catalysed rearrangement of phenylhydroxy-lamines, known as the Bamberger rearrangement, is useful for the synthesis of 4-aminophenols (Scheme 4.3). 

The oxidative rearrangement of various acylbenzenes with alkaline hydrogen peroxide (the Dakin reaction) can provide a mild method for the synthesis of phenols (Scheme 4.15). 

The mechanism is the same as that of the Dakin reaction of aromatic aldehydes (equation 359). The reaction is acid-catalyzed. The peroxy acid transfers oxygen onto the carbon of the carbonyl group and generates an unstable intermediate. A rearrangement of the groups bonded to the original carbonyl carbon results in the formation of esters or, with cyclic ketones, lactones [262, 303] (equation 379). 

Wesselv-Moser Rearrangement West (see Dakin-West Reaction)... 

The oxidation of aromatic aldehydes could be complicated. In addition to direct oxidation to the dicarboxylic acid (phthalic acid), an aromatic aldehyde carbonyl could also be oxidized and then rearranged and hydrated to form a phenol via aryl formates (Dakin reaction)." Thus, when treating p-hydroxy-benzaldehyde, 25, with basic hydrogen peroxide, the following mechanism is actually involved (Fig. 10). 

Dakin-West reaction 172 Darzens reaction 21 Dilthey synthesis (pyrylium ion) 302 Dimroth rearrangement 261 Doebner-Miller synthesis (isoquinoline) 400... 

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