Kinetics and mechanism of the alkali catalysed condensation of <i>o</i>‐ and <i>p</i>‐methylol phenols by themselves and with phenol

Francis, D. Joseph; Yeddanapalli, L. M.

doi:10.1002/macp.1962.020550106

Cited by 47 publications

(6 citation statements)

References 11 publications

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“…b, in which the carbocation is a powerful electrophile. The reaction is considered to occur between a neutral monomer and an anionic monomer . One possible mechanism involves the attack of the electron‐rich, hydroxymethyl substituted ring carbon by a QM carbocation with subsequent emission of a formaldehyde molecule as illustrated in Fig.…”

Section: Discussionsupporting

confidence: 83%

“…For the phenolate salts of 2‐HMP and 4‐HMP, the 13 C chemical shifts for the substituted ring carbons are found in the range of 129.62 to 130.12 ppm for 2‐HMP and 126.85 to 128.68 ppm for 4‐HMP. The higher electron density of the 4‐HMP ring carbon is in accord with the established self‐condensation reactivity order of 4‐4′ > 4‐2′ > 2‐2′ …”

Section: Discussionsupporting

confidence: 83%

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Chemical shifts of phenolic monomers in solution and implications for addition and self‐condensation

Haupt

Renneckar

2012

Magnetic Reson in Chemistry

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Alkali metal counter-cations alter the electron density of phenolates in solution by electrostatic interactions. This change in electron density affects their reactivity toward formaldehyde, hydroxymethylphenols, and isocyanates during polymerization. The electronic perturbation of phenolic model compounds in the presence of alkali metal hydroxides was investigated with (13)C and (1)H nuclear magnetic resonance in polar solvents relative to non-ionic controls, altering the chemical shifts of the model compounds, thus indicating changes in electron density using the chemical shift as a proxy. These shifts were attributed to Coulombic electrostatic interactions of the counter-cation with the phenolate anion that correlated to hydrated ionic radius and solvent dielectric constants. The predicted relative reaction rates for formaldehyde addition based on electron density ranking from (13)C nuclear magnetic resonance of the phenolic models was compared with the literature values. Predictions for condensation reactions of 2- and 4-hydroxymethylphenol from chemical shifts were consistent with published results. The results permit predictions for the reaction of phenolic compounds for the formation of thermosetting polymeric materials.

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Section: Discussionsupporting

confidence: 83%

Section: Discussionsupporting

confidence: 83%

Chemical shifts of phenolic monomers in solution and implications for addition and self‐condensation

Haupt

Renneckar

2012

Magnetic Reson in Chemistry

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“…The S N 2 mechanism shown in Figure 2 as reaction (2) was also suggested by some early reports [9,10,11,12,13]. However, in the study of Higuchi et al on the self-condensation of 2-HMP ( o -HMP) [15], the authors concluded that the reaction is of genuine first-order and any bimolecular mechanism should be ruled out.…”

Section: Resultsmentioning

confidence: 62%

“…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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“…From eqs. (5) and (8) it has been found that kl = nk. Thus, k l was calculated with the help of the overall rate constant k .…”

Section: Calculation Of Stepwise Rate Constants P-cresol Reacts With mentioning

confidence: 98%

Kinetics and mechanism of the alkali‐catalyzed p‐cresol–formaldehyde reaction

Malhotra

Kumar

1979

J of Applied Polymer Sci

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SynopsisThe kinetics of the reaction of p-cresol with formaldehyde in relation to the functionality of p-cresol using NaOH as catalyst has been studied at temperatures of (65 f O.O5)OC, (70 f O.O5)OC, (75 f O.O5)OC, and (80 f 0.05)OC. The pH maintained was 7.0,S.O. 9.0,9.4, and 10.0. The reaction follows a second-order rate law. The rate was found to increase with increase in pH. The stepwise rate constants ( k 1 and k z ) for the formation of monomethylol-p-cresol and dimethylol-p-cresol, respectively, were calculated from the overall rate constant k. The values of Arrhenius parameters and the entropy of activation for the overall as well as the stepwise reactions were calculated. The experimental and calculated values of k at pH 10.0 and temperatures 65,70,75, and 80°C were found to agree well within experimental errors. A mechanism conforming to the energies and entropies of activation of the reaction is suggested.

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Kinetics and mechanism of the alkali catalysed condensation of o‐ and p‐methylol phenols by themselves and with phenol

Cited by 47 publications

References 11 publications

Chemical shifts of phenolic monomers in solution and implications for addition and self‐condensation

Chemical shifts of phenolic monomers in solution and implications for addition and self‐condensation

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

Kinetics and mechanism of the alkali‐catalyzed p‐cresol–formaldehyde reaction

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