The Dakin oxidation (or Dakin reaction) is an organic redox reaction in which an ortho- or para-hydroxylated phenyl aldehyde (2-hydroxybenzaldehyde or 4-hydroxybenzaldehyde) or ketone reacts with hydrogen peroxide in base to form a benzenediol and a carboxylate. Overall, the carbonyl group is oxidised, whereas the H2O2 is reduced. The Dakin oxidation, which is closely related to the Baeyer–Villiger oxidation, is not to be confused with the Dakin–West reaction, though both are named after Henry Drysdale Dakin. Reaction mechanism The Dakin oxidation starts with nucleophilic addition of a hydroperoxide anion to the carbonyl carbon, forming a tetrahedral intermediate (2). The intermediate collapses, causing [1,2]-aryl migration, hydroxide elimination, and formation of a phenyl ester (3). The phenyl ester is subsequently hydrolyzed: nucleophilic addition of hydroxide from solution to the ester carbonyl carbon forms a second tetrahedral intermediate (4), which collapses, eliminating a phenoxide (5) and forming a carboxylic acid. Finally, the phenoxide extracts the acidic hydrogen from the carboxylic acid, yielding the collected products (6). Factors affecting reaction kinetics The Dakin oxidation has two rate-limiting steps: nucleophilic addition of hydroperoxide to the carbonyl carbon and [1,2]-aryl migration. Therefore, the overall rate of oxidation is dependent on the nucleophilicity of hydroperoxide, the electrophilicity of the carbonyl carbon, and the speed of [1,2]-aryl migration. The alkyl substituents on the carbonyl carbon, the relative positions of the hydroxyl and carbonyl groups on the aryl ring, the presence of other functional groups on the ring, and the reaction mixture pH are four factors that affect these rate-limiting steps. Alkyl substituents In general, phenyl aldehydes are more reactive than phenyl ketones because the ketone carbonyl carbon is less electrophilic than the aldehyde carbonyl carbon. The difference can be mitigated by increasing the temperature of the reaction mixture. Relative positions of hydroxyl and carbonyl groups O-hydroxy phenyl aldehydes and ketones oxidize faster than p-hydroxy phenyl aldehydes and ketones in weakly basic conditions. In o-hydroxy compounds, when the hydroxyl group is protonated, an intramolecular hydrogen bond can form between the hydroxyl hydrogen and the carbonyl oxygen, stabilizing a resonance structure with positive charge on the carbonyl carbon, thus increasing the carbonyl carbon’s electrophilicity (7). Lacking this stabilization, the carbonyl carbon of p-hydroxy compounds is less electrophilic. Therefore, o-hydroxy compounds are oxidized faster than p-hydroxy compounds when the hydroxyl group is protonated. M-hydroxy compounds do not oxidize to m-benzenediols and carboxylates. Rather, they form phenyl carboxylic acids. Variations in the