The mechanism of chain growth in oxidative polycondensation of phenols

Ionescu, Mariana S.; Mihis, Ana Bianca

doi:10.1002/masy.19971220139

Cited by 5 publications

(2 citation statements)

References 11 publications

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“…As such a pathway, the rearrangement of the quinone ketal has been proposed, , as drawn schematically in Figure . This rearrangement is a concerted process, in fact a Claisen rearrangement, which is a special case of sigmatropic transposition, as elaborated upon by Ionescu et al This rearrangement results in the quinone group being shifted over the backbone of the oligomeric species, until eventually the end is reached and a phenol is formed by tautomerisation of the hemiketal. It is clear that this process cannot take place within the coordination sphere of copper, since the reaction involves the carbonyl head of the quinone ketal.…”

Section: Resultsmentioning

confidence: 99%

The Course of the Copper-Catalyzed Oxidative Polymerization of 2,6-Dimethylphenol. Analysis of Oligomeric Phenols during the Coupling Reaction

et al. 1998

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The course of the copper-catalyzed oxidative coupling of 2,6-dimethylphenol (DMP) has been studied by HPLC-analysis of reaction mixtures which had started with either DMP itself, or with its C−O coupled dimer, 4-(2‘,6‘-dimethylphenoxy)-2,6-dimethylphenol, under both aerobic and anaerobic conditions. These measurements have provided information on how the actual phenol coupling step takes place and how the polymerization reaction proceeds. In reactions started with the monomer, no or at most very small amounts of oligomers of DMP are detected, apart from a precipitate of polymeric material in the aerobic experiments. Reactions started with the dimer only result in swift formation of significant amounts of monomer in addition to oligomers. This difference in behavior can be ascribed to the higher reactivity of oligomeric phenols compared to the monomer. The fact that monomer phenol is formed from dimer phenol is strong evidence for a reaction pathway in which a quinone ketal is formed by C−O coupling of two phenolic moieties. It is believed that as long as this quinone remains coordinated to the copper, it can decompose by (probably heterolytic) fission of one of the ether bonds to generate two (new) species, de facto resulting in redistribution of the oligomers. Once the quinone dissociates from the copper catalyst, a rearrangement may occur to afford the C−O coupled phenol. Methylated phenols (anisoles) do not take part in either redistribution or rearrangement reactions, since a quinone ketal can only be formed from species that can be deprotonated, i.e., from phenols.

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Section: Resultsmentioning

confidence: 99%

The Course of the Copper-Catalyzed Oxidative Polymerization of 2,6-Dimethylphenol. Analysis of Oligomeric Phenols during the Coupling Reaction

et al. 1998

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“…This mechanism can be divided into rearrangement and redistribution steps. The rearrangement is a concerted Claisen‐type rearrangement, which is a special case of a sigmatropic rearrangement proposed by Ionescu et al16 This rearrangement results in the quinone group being shifted over the backbone of the oligomeric species, until eventually the end is reached. According to this mechanism, two dimeric phenols could give a tetramer as the primary product.…”

Section: Introductionmentioning

confidence: 95%

Depolymerization of Poly(2,6‐dimethyl‐1,4‐phenylene oxide) under Oxidative Conditions

Saito

Masuyama

Oyaizu

et al. 2003

Chemistry A European J

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Depolymerization of an engineering plastic, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), was accomplished by using 2,6-dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (M(n)=1.0x10(4), M(w)/M(n)=1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to M(n)=4.9x10(2) (M(w)/M(n)=1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.

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Voltammetric investigation of β-estradiol

Salcı

Biryol

2002

Journal of Pharmaceutical and Biomedical Analysis

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The mechanism of chain growth in oxidative polycondensation of phenols

Cited by 5 publications

References 11 publications

The Course of the Copper-Catalyzed Oxidative Polymerization of 2,6-Dimethylphenol. Analysis of Oligomeric Phenols during the Coupling Reaction

The Course of the Copper-Catalyzed Oxidative Polymerization of 2,6-Dimethylphenol. Analysis of Oligomeric Phenols during the Coupling Reaction

Depolymerization of Poly(2,6‐dimethyl‐1,4‐phenylene oxide) under Oxidative Conditions

Voltammetric investigation of β-estradiol

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