Kinetics and Mechanisms of the Condensation Reactions of Phenolic Resins II. Base-Catalyzed Self-Condensation of 4-Hydroxymethylphenol

Higuchi, Mitsuo; Yoshimatsu, Takehiro; Urakawa, Takashi; Morita, Mitsuhiro

doi:10.1295/polymj.33.799

Cited by 13 publications

(17 citation statements)

References 7 publications

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“…The kinetics and mechanisms of the individual reactions in the PF system are apparently the key issues and also the foundation for understanding the chemistry of PF. However, by surveying the literature from the middle of the last century to recent years, discrepant results for the kinetics and mechanisms of the base-catalyzed condensation reactions between hydroxymethylphenols (HMPs) have been reported [9,10,11,12,13,14,15,16,17,18,19]. In some earlier studies, the condensations of HMPs were reported to be first-order [9,10,11], pseudo-first-order or second-order [12,13].…”

Section: Introductionmentioning

confidence: 99%

Theoretical Confirmation of the Quinone Methide Hypothesis for the Condensation Reactions in Phenol-Formaldehyde Resin Synthesis

Cao

Liang

et al. 2017

Polymers

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Abstract:The mechanisms for the base-catalyzed condensation reactions in phenol-formaldehyde resin synthesis were investigated by using the density functional theory method. The structures of the intermediates and transition states, as well as the potential energy barriers of the involved reactions, were obtained. The hypothesis of quinine methide (QM) formation was theoretically confirmed. Two mechanisms were identified for QM formation, namely E1cb (elimination unimolecular conjugate base) and water-aided intra-molecular water elimination. The latter is energetically more favorable and is proposed for the first time in this work. Based on the QM mechanism, the condensation should be a unimolecular reaction because the following condensation between an ionized species (dissociated phenol or hydroxymethylphenol) with QM is much faster. The previously proposed S N 2 condensation mechanism was found to be not competitive over the QM mechanism due to a much higher energy barrier. The condensation reaction between neutral phenol or hydroxymethylphenol and QM was also found to be possible. The energy barrier of this reaction is close to or higher than that of QM formation. Therefore, the overall condensation reaction may appear to be bimolecular if such a reaction is incorporated. The theoretical calculations in this work rationalized the discrepant results reported in previous kinetics studies well.

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Section: Introductionmentioning

confidence: 99%

Theoretical Confirmation of the Quinone Methide Hypothesis for the Condensation Reactions in Phenol-Formaldehyde Resin Synthesis

Cao

Liang

et al. 2017

Polymers

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“…The former functional groups are evidence of the involvement of some products of glycerol conversion in the polymerisation reaction over iron catalysts. As previously reported, graphical methods based on the integral of the rate equation apply to those cases where reaction products have no influence on the course of the polymerisation [27]. The formation of different structures in the current investigation when comparing to those glycerol polymerisation studies could be explained based on the reaction temperature which favours the formation of acrolein and other products in contrast to previously reported processes where this parameter does not exceed 180 °C [2].…”

Section: Insights On the Mechanism Of Formation Of The Building Blockmentioning

confidence: 47%

Catalytic conversion of glycerol to polymers in the presence of ammonia

Sánchez

Gaikwad

Holdsworth

et al. 2016

Chemical Engineering Journal

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In this contribution, the development of a process for the synthesis of potentially highly valuable polymeric products from the reaction of waste glycerol with ammonia is reported for the first time. The polymers were the result of a single step, continuous gas phase process, catalysed by an alumina-supported iron catalyst, operating under relatively mild reaction conditions. The solid product was characterised using 1D and 2D NMR spectroscopy, FTIR spectroscopy, qualitative chemical tests and elemental analysis. Characterisation revealed building blocks with unsaturated, amido and ester functionalities shaping a mixture of polymers. Nitrogen atoms were present in the main chain of the resultant polymers. NMR analyses of the polymer denotes the formation of structural defects such as unsaturation and branching; while the partial solubility of the polymer in solvents such as CDCl 3 and THF is indicative of the formation of cross-linked structures. Insights into the mechanism of formation of these functional groups were based on the liquid and gas phase product distribution. Polymers with chain structures similar to those synthesised in this work are currently manufactured from fossil fuels and are widely used in biomedical applications not 2 only because of their architecture but also due to their response to changes in pH and temperature.

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“…Pathway (II) demonstrates the mechanism that forms the intermediates D , E and F for the base-catalyzed phenol-formaldehyde reaction. Among them, the quinine methide is the widely accepted intermediate that is involved in the condensations [40,41,42]. Based on these intermediates, the mechanisms for the UF and PF condensation reactions were proposed in Figure 3.…”

Section: Resultsmentioning

confidence: 99%

A 13C-NMR Study on the 1,3-Dimethylolurea-Phenol Co-Condensation Reaction: A Model for Amino-Phenolic Co-Condensed Resin Synthesis

Cao

Liang

et al. 2016

Polymers

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Abstract:The reactions of di-hydroxymethylurea with phenol under alkaline (pH = 10), weak (pH = 6) and strong acidic (pH = 2) conditions were investigated via the 13 C-NMR method. Based on the proposed reaction mechanisms, the variations of the structures of different condensed products were analyzed and the competitive relationship between self-and co-condensation reactions was elucidated. The required experimental conditions for co-condensations were clearly pointed out. The main conclusions include: (1) the self-condensation between urea formaldehyde (UF) or phenol formaldehyde (PF) monomers were dominant while the co-condensations were very limited under alkaline conditions. This is because the intermediates produced from urea, methylolurea and phenol are less reactive in co-condensations with respect to self-condensations; (2) under weak acidic conditions, the self-condensations occurred exclusively among the UF monomers. The co-condensation structures were not observed; and (3) the co-condensations became much more competitive under strong acidic conditions as the relative content of the co-condensed methylenic carbon accounts for 53.3%. This result can be rationalized by the high reactivity of the methylolphenol carbocation intermediate toward urea and methylolurea. The revealed reaction selectivity and mechanisms may also be applied to the synthesis of those more complex co-condensed adhesives based on natural phenolic and amino compounds.

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Kinetics and Mechanisms of the Condensation Reactions of Phenolic Resins II. Base-Catalyzed Self-Condensation of 4-Hydroxymethylphenol

Cited by 13 publications

References 7 publications

Theoretical Confirmation of the Quinone Methide Hypothesis for the Condensation Reactions in Phenol-Formaldehyde Resin Synthesis

Theoretical Confirmation of the Quinone Methide Hypothesis for the Condensation Reactions in Phenol-Formaldehyde Resin Synthesis

Catalytic conversion of glycerol to polymers in the presence of ammonia

A 13C-NMR Study on the 1,3-Dimethylolurea-Phenol Co-Condensation Reaction: A Model for Amino-Phenolic Co-Condensed Resin Synthesis

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