Oxidants 4-methoxyphenol

The previous examples have invariably involved the 4-position but where this is substituted as in the case of 4-methoxyphenol, oxidative coupling can take place at the 2-position probably via an intermediate phenoxide ion without... 

Eugenol, 4 allyl-2-methoxy phenol, is capable of forming cements with ZnO, CuO, MgO, CaO, CdO, PbO and HgO (Brauer, White Moshonas, 1958 Nielsen, 1963). Other 2-methoxy phenols are also capable of forming cements with metal oxides, provided the allyl group is not in a 3- or 6-position where it sterically hinders the reaction (Brauer, Argentar Durany, 1964). These include guaiacol, 2-methoxyphenol, and the allyl and propylene 2-methoxy phenols. 

In polar solvents, this reaction is fast. For instance, at 333 K/ -methoxyphenol is oxidized by cumyl hydroperoxide in chlorobenzene and a mixture of chlorobenzene tert-butanol = 4 1 with kn = 3.5 x 10-6 and 2.5 x 10-4 Lmol-1 s 1, respectively [124]. The acceleration of this... 

In aqueous solutions, ROOH can react with p-methoxyphenol at pH > 8 however, at pH >10 the reaction slows down due to ROOH dissociation and a weak oxidative ability of the ROz anion. 

The combined addition of two phenols, one of which is sterically hindered, for example, 2,6-bis(l,l-dimethylethyl)phenol, and another is sterically nonhindered also leads to a synergistic effect [35-38]. As found by Mahoney [35], 2,4,6-tris(l,l-dimethylethyl)phenol with a concentration of 10 4 L mol 1 does not virtually inhibit the initiated oxidation of 9,10-dihydroan-thracene (333 K), but /)-methoxyphenol, taken in the same concentration, does inhibit oxidation. The induction period doubles if two phenols are added together in equal concentrations, which indicates that both phenols are involved in chain termination. The mechanism of synergistic action can be explained by the following kinetic scheme [35] ... 

These compounds contain a furan ring fused to a benzene moiety in the 2,3-position. This synthesis was also described by Flynn et al. [73] and is shown in Scheme 25 involved the coupling of 2-iodo-5-methoxyphenol 104, 4-methoxyphenylethyne 105 to form the intermediate o-alkynylphenolate 106. Aryl iodide 107 was added to the phenolate in DMSO with heat. Oxidative addition, palladium(II)-induced cyclization and reductive elimination resulted in the product 108 with an 88% yield. 

Oxidation of parti-methoxyphenols.2 The last step in a synthesis of cyano-cycline A (1) requires oxidation of the para-methoxyphenol (2) to a quinone. This reaction is effected in highest yield (55%) with manganese(III) acetate (0.3%H2SO4-CH3CN). 

Although permanganate ions are not generally used to effect oxidative coupling of phenols, it has been shown that, in the presence of a catalyst in an organic solvent, 2-methoxyphenols are coupled oxidatively under very mild conditions to produce the dimeric products (>50%) [48], Unsaturated substituents are not oxidized under the mild conditions. 

The photolysis of 4-nitroanisole in degassed acetonitrile or benzene yields 4-nitro-soanisole and 2-nitro-4-methoxyphenol is). Triphenylene (Et = 67 kcal mole i 4-nitroanisole t=59.5 kcal mole i has been used to sensitize the reaction, which is suppressed completely by nitric oxide. A rationale for the formation of the products observed is given below. 

The voltammetric response of curcumin and carthamin must, in principle, be dominated by the oxidation of the phenol and/or methoxyphenol groups (see Scheme 2.2). The electrochemistry of methoxyphenols has claimed considerable attention because of their applications in organic synthesis [159-163]. As studied by Quideau et al., in aprotic media, 2-methoxyphenols are oxidized in two successive steps into cyclohexadienone derivatives [163], whereas a-(2)- and a-(4-methoxyphenoxy) alkanoic acids undergo electrochemically induced spirolac-tonization to develop synthetically useful orthoquinone bis- and monoketals. In the presence of methanol, the electrochemical pathway involves an initial one-electron loss, followed by proton loss, to form a monoketal radical. This undergoes a subsequent electron and proton loss coupled with the addition of alcohol to form an orthoquinone monoketal. The formal electrode potential for the second electron transfer... 

Sopchak D, Miller B, Avygal Y, Kalish R (2002) Rotating ring-disk electrode studies of the oxidation of p-methoxyphenol and hydroquinone at boron-doped diamond electrodes. J. Electroanal Chem 538 39-45. 

Borras, C, Rodriguez P, Laredo T, Mostany J, Scharifker BR (2004) Electrooxidation of aqueous p-methoxyphenol on lead oxide electrodes. J Appl Electrochem 34 583-589. 

As normally supplied, acrylic esters are inhibited to enhance the shelf life. Aside from dissolved oxygen, inhibitors that are deliberately added include phenolic compounds such as hydroquinone (HQ) and p-methoxyphenol (MEHQ, i.e., methyl ether of hydroquinone ). These inhibitors are usually present in concentrations of 50 to 100 parts per million (ppm) by weight. Oxidation products of the phenolic inhibitors may also be present. 

Potent antileukemic agent, asatone (11), which was isolated from Asarum taitonense Hayata, was synthesized via dimerization of cyclohexa-2,4-dienone (138) generated by PIDA oxidation of o-methoxyphenol (137) [94] (Scheme 11). 

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