Dakin reaction aromatic aldehydes

What product will actually form Will catechol form via the Dakin reaction Aromatic aldehydes in Dakin reactions usually need to have an electron-donating group, like hydroxyl, alkoxyl or amino groups, in the ortho- or para- positions. This is illustrated in a few more examples shown below (Fig. 12). ... 

The most important applications of peroxyacetic acid are the epoxi-dation [250, 251, 252, 254, 257, 258] and anti hydroxylation of double bonds [241, 252, the Dakin reaction of aldehydes [259, the Baeyer-Villiger reaction of ketones [148, 254, 258, 260, 261, 262] the oxidation of primary amines to nitroso [iJi] or nitrocompounds [253], of tertiary amines to amine oxides [i58, 263], of sulfides to sulfoxides and sulfones [264, 265], and of iodo compounds to iodoso or iodoxy compounds [266, 267] the degradation of alkynes [268] and diketones [269, 270, 271] to carboxylic acids and the oxidative opening of aromatic rings to aromatic dicarboxylic acids [256, 272, 271, 272,273, 274]. Occasionally, peroxyacetic acid is used for the dehydrogenation [275] and oxidation of aromatic compounds to quinones [249], of alcohols to ketones [276], of aldehyde acetals to carboxylic acids [277], and of lactams to imides [225,255]. The last two reactions are carried out in the presence of manganese salts. The oxidation of alcohols to ketones is catalyzed by chromium trioxide, and the role of peroxyacetic acid is to reoxidize the trivalent chromium [276]. 

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 ... 

In another kind of reaction, an aromatic aldehyde ArCHO or ketone ArCOR is converted to a phenol ArOH on treatment with alkaline H202, but there must be an OH or NH2 group in the ortho or para position. This is called the Dakin reac-The mechanism may be similar to that of the Baeyer-Villiger reaction (18-19) ... 

Figure 3.42 Dakin reaction of aromatic aldehydes to phenols in the presence of alkaline hydrogen peroxide.

The intermediate 27 has been isolated." The reaction has been performed on aromatic aldehydes with an alkoxy group in the ring, and no OH or NH2. In this case, acidic H2O2 was used." The Dakin reaction has been done in ionic liquids. 

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). 

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. 

This reaction is called the Dakin reaction, and requires a hydroxyl or amino group in the ortho or para position of the aromatic aldehyde. One possible reason why such substituents might help this reaction is the hypothesis that a cyclic intermediate is formed that comprises the former aldehyde carbon, the carbon in the aromatic ring to which it is attached and the oxygen atom that is the migration terminus. A+M group in either the ortho or para position would facilitate the formation of such a ring. 

In the Dakin reaction, an aromatic aldehyde, which has a hydroxyl or amino group in the ortho or para position of the aromatic aldehyde, can be oxidised by hydrogen peroxide to yield the corresponding phenol. 

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. 

In a variation of the Bayer Villiger reaction, known as the Dakin reaction, the oxidation of aromatic aldehydes to phenols is accomplished via aryl formate... 

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. ... 

Aromatic aldehydes having hydroxyl group in ortho or para position to the formyl groups can be oxidised with alkaline (Dakin reaction) in low yields. This reaction has been recently carried out in high yields using sodium percarbonate (SPC Na COj, 1.5 H O ) in H, 0-THF under ultrasonic irradiation. Using this procedure following aldehydes have been oxidised in 85-95% yields o-hydroxybenzaldehyde p-hydroxybenzaldehyde 2-hydroxy-4-methoxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde and 3-methoxy-4-hydroxybenzaldehyde. 

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). 

Figure 10. An example of the Dakin reaction an aromatic aldehyde is converted to a phenol.

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