Alkylphenols reaction mechanism

Assuming that ks = k9 = 3x 108Lmol 1s 1 (the key value), the diversity of the rate constants of the reactions of phenols and phenoxyl radicals (7, —7, 10, 11, and 12) can be reduced to only two parameters, k7 and T. This allows one to get the universal formulae for the oxidation rate v, into which these parameters enter as functions of k2, k7, T, and ambient conditions (Table 14.7). When considering this table, it should be taken into account that mechanism VII is possible only for 2,4,6-tris-alkylphenols, while mechanism IX holds only for o- and p-alkoxyphenols. 

Further to its ability to perform allylic and benzylic oxidations,149 /-butylpcroxy-iodane (6) effects radical oxidation of 4-alkylphenols to give 2,5-cyclohexadien-l-ones under mild conditions in good yields.150 o,o-Coupling dimers as side products and inhibition of the reaction by added galvinoxyl radical scavenger support a radical oxidation mechanism. 

The rearrangement reaction of a variety of alkyl phenyl ethers over a dealumi-nated HY zeolite has been shown to involve both intramolecular and intermolecular processes to afford phenol, (alkoxyalkyl)benzenes and alkylphenols as the main products. o-Benzylphenol has been obtained as the exclusive product in the rearrangement of benzyl phenyl ether in the presence of montmorillonite. The mechanism for a novel zeolite /3-catalysed rearrangement of alkoxybenzyl allyl ethers to aldehydes and ketones has been investigated by the use of cross-over reactions and deuterium labelling. The reaction was found to be mainly intramolecular and has been described as a nucleophilic attack of the double bond on the electrophilic benzylic carbon of the ether-Lewis acid complex, followed by a... 

Alkylphenols can be converted to p-BQ using dioxygen and HPA- ( =2-6) [121]. Oxidation of TMP in AcOH-HjO (95/5) produced TMBQ with a selectivity of 86% at complete TMP conversion [121a]. The main reaction by-product was 2,2, 3,3, 5,5 -hexamethyl-4,4 -biphenol. Based on kinetic and spectroscopic studies, a stepwise mechanism that involves dissociation of HPA-w in the acidic medium generating the active species VOj, oxidation of TMP by VOj to produce phenoxyl radical and VCP+ followed by reoxidation of V(fV) to V( V) with in the coordination... 

The simplest p-alkylphenol is p-cresol (35), which has a methyl substituent. One of the first detailed studies of the HRP-catalyzed oxidation of p-cresol was reported in 1976 [51]. Recently, a detailed in situ NMR analysis revealed details of the coupling mechanism of the p-cresol polymerization. NMR and H- H gCOSY 2D NMR analysis suggested that ortho-ortho coupling (43) is the dominant coupling mechanism at the initial stage of the polymerization. The consumption of dimer accelerated only after the complete conversion of the monomer in the reaction mixture. After a reaction time of about 75 min, the formation of Pummerer s ketone (44) was observed. These ketonic species are formed from ortho-para-coupled dimers by intramolecular Michael addition. They are probably not able to participate in the further polymerization process and remain as side products (Scheme 9) [76]. Experiments with 4-propylphenol have revealed that the formation of Pummerer s ketone may be suppressed at lower temperatures [112]. 

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