DAKIN Phenol Oxidation

The conversion of benzaldehydes to phenols using alkaline hydrogen peroxide is generally known as the Dakin s oxidation . However, this reaction is limited... 

Alkaline hydrolysis of benzal acetone structures to the corresponding aldehyde (XIX) and acetone and subsequent oxidation of the aldehyde (XIX) to the corresponding benzoic acid (V) do not seem to represent an actual degradation stage since oxidizing the aldehyde (XIX) under our mild standard conditions yielded only traces of the corresponding benzoic acid (V). The aldehyde (XIX) was rapidly decomposed via Dakin reaction to formic acid and 3-methoxy-S-methyl-o-benzoquinone, which is immediately degraded to phenolic humic compounds. 

The Dakin Reaction allows the preparation of phenols from aryl aldehydes or aryl ketones via oxidation with hydrogen peroxide in the presence of base. The aryl formate or alkanoate formed as an intermediate is subsequently saponified to yield the substituted phenol product. 

Aldehydes which contain electron-releasing substituents in the ortho or para position give phenol products via a formate intermediate. This reaction is known as the Dakin reaction, the oxidation of salicylaldehyde being a classic example (Figure 3.42).215... 

Although alkaline conditions are normally employed, for reasons of safety it is occasionally advantageous to operate under neutral conditions where, for example, oxidation of benzaldehydes to benzoic acids may be desired rather than the Dakin reaction.210 Conversely alkyl benzaldehydes, which under most conditions would be expected to yield the corresponding benzoic acids, have been reported to undergo the Dakin-type reaction yielding alkyl phenols in the presence of strong acids.220... 

Peroxysulfuric acid, PBA and MPPA, common reagents of the past, appear less frequently in the current literature. Basic 30% hydrogen peroxide or r-butylhydroperoxide have special utility for oxidation of cyclobutanones and strained, bridged cycloalkanones to lactones. Basic 3- % hydrogen peroxide is used in the Dakin oxidation of aryl aldehydes to phenols, while peroxymonophosphoric acid oxidizes aryl ketones to phenolic acetates. ... 

Dihydroxybenzene may be prepared from 2-hydroxybenzaldehyde by the Dakin reaction, which involves oxidation in alkaline solution by hydrogen peroxide (Scheme 4.15). The reaction involves a 1,2-shift to an electron-deficient oxygen and is similar to the cumene process used to synthesize phenol (Section 4.2). 

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). 

M.E. Jung and co-workers have developed a synthesis of selectively protected L-Dopa derivatives from L-tyrosine via a Reimer-Tiemann reaction followed by the modified Dakin oxidation. The formyl group introduced by the Reimer-Tlemann reaction had to be converted to the corresponding phenol. After trying many sets of conditions, the Syper process was chosen, which uses arylselenium compounds as activators for the oxidation. Treatment of the aromatic aldehyde with 2.5 equivalents of 30% hydrogen peroxide in the presence of 4% diphenyl diselenide in dichloromethane for 18h gave the aryl formate in excellent yield. This ester was cleaved by treatment with methanolic ammonia for 1h to afford the desired phenol in good yield. 

Dakin oxidation Conversion of aromatic aldehydes and ketones to the corresponding phenols. 118... 

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). 

The oxidation of aromatic aldehydes to phenols via the aryl formates is known as the Dakin reaction and is evidently related to the Baeyer-Villiger oxidation of ketones. The use of MCPBA is well known [45]. The successful use of MMPP and UHP-acetic anhydride in these reactions (Eqs. 34 to 36) can be achieved with aromatic aldehydes that have an electron releasing substituent in an ortho- or para-position. In the absence of a suitable electron releasing substituent, aromatic aldehydes are oxidised to the corresponding carboxylic acid. 

The iodized protein does not exhibit specific binding Often, the incorporated iodine is to blame, but the reagents used for the iodination can also inactivate the protein. For example, chloramine T oxidizes not only 1 but the a-amino group of peptides and amino acids to nitrile. Sensitive phenol derivatives are also destroyed. By the way, these reactions were the basis for the application of chloramine T as a disinfectant during World War I (Dakin et al. 1996). 

This reaction was initially reported by Dakin in 1909. It is the preparation of phenols from aryl aldehydes or aryl ketones involving the oxidation of corresponding aromatic compounds by hydrogen peroxide in the presence of a base and subsequent hydrolysis of the aryl formate or alkylcarboxylate intermediates. Therefore, this reaction is generally known as the Dakin reaction. It has been reported that the para-or ortho- substituents (such as OH, NH2) on aryl aldehydes or aryl ketones will facilitate this reaction, especially for the ortho OH group, which accelerates the reaction via the formation of an intfamolecular hydrogen bonding. ... 

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