Vinyl-phenol formation mechanism

Fig. 8.7. Vinyl-phenol formation mechanism in must clarified using a pectinase preparation with cinnamate esterase...

Both the above mechanisms are proposed in the literature with Mannich bases of nitroalkanes the substitution is clearly favored by the steric hindrance of the amine moiety, thus suggesting path 1, - whereas NMR studies on the reaction of P-amino-ketones with hydroxy coumarins do not reveal the presence of vinyl ketone intermediates. lodomethylated phenolic Mannich bases arc also claimed to react according to path 2, although the formation as by-products of dimers and methylene-bis-derivatives accounts for the participation of methylenequinone intermediates in the process. "... 

Evans et al. (10) have shown that OH radicals produced by the Fenton reagent can initiate the polymerization of vinyl compounds and that the OH radicals, which in the first instance attack the double bond of the monomer, are built into the polymer chain. Stein and Weiss (45) have used the hydroxylation of benzene and of other simple aromatic compounds (e.g., benzoic acid and nitrobenzene) to detect these radicals. In the action of OH radicals on benzene in aqueous systems the formation of phenol and of diphenyl indicated a free radical mechanism of the following type ... 

The effect on the ageing of ethylene-vinyl acetate copolymer has been studied [46]. Mechanisms are suggested for the formation of the various oxidative groups found. Combinations of phenolic antioxidants with phosphates give greatest protection against discolouration, which is consistent with a proposed free radical oxidation process of deacetylation. 

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