Condensation reactions of phenolic resins III: self-condensations of 2,4-dihydroxymethylphenol and 2,4,6-trihydroxymethylphenol (1)

Abstract

This study reexamined the kinetics of the condensation reactions of hydroxymethylphenols with the purpose of elucidating the reaction mechanisms. This report discusses experimental results on the self-condensations of 2,4-dihydroxymethylphenols (2,4-DHMP) and 2,4,6trihydroxymethylphenol (THMP), focusing on the order of reaction. The relations between the initial rates of reaction and the initial concentrations of reactants were investigated. Results quite different from those of previous reports were obtained. The order of reaction of the selfcondensation of 2,4-DHMP was found to be 1.1, which did not change with the alkali/2,4-DHMP molar ratio. The order of reaction of the self-condensation of THMP was found to vary with both the concentration of THMP and the alkali/THMP molar ratio. In the region of THMP concentrations above 1.5 mol/1, the order of reaction was confirmed to be 2.0, which did not change with the alkali/THMP molar ratio. In the region of THMP concentrations below 1.0 mol/1, the order of reaction varied with the alkali/THMP molar ratio, showing fractional numbers of 1.2-1.6. These results indicate that unimolecular reaction(s) and bimolecular reaction(s) take place simultaneously as the ratedetermining step in the condensation reactions of 2,4-DHMP and THMP and that the reaction mechanism changes with the species of reactant and, in some cases, with the reaction conditions.

Condensation reactions of phenolic resins. VI. Dependence of the molecular association of 2,4,6‐trihydroxymethylphenol on the concentration in an aqueous alkaline medium

“…The inflection point at the concentration of 1.2 mol/L agreed with that shown in Figure 2. Moreover, the inflection at this concentration is similar to the phenomenon obtained from the kinetic experiment of Kamo et al, 9 indicating the change in the molecular interaction. Higher values of E a reflect a strong dependence of T 1 on the temperature, indicating that the hydroxymethyl group is easy to rotate.…”

“…Considering these results together with previous kinetic works, 9,10 we assume a reaction pathway for the self-condensation of THMP (Fig. 5).…”

“…The behavior of monomeric HMPs as model compounds is easier to study. In previous works, the kinetics of the self-condensations of 2-hydroxymethylphenol, 7 4-hydroxymethylphenol, 8 2,4-dihydroxymethylphenol, and 2,4,6-trihydroxymethylphenol (THMP) 9,10 were investigated. At THMP concentrations greater than 1.5 mol/ L, the reaction order was 2.0, whereas at concentrations below 1.0 mol/L, the reaction order changed to values between 1.2 and 1.6.…”

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

“…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].…”

“…In 2001, Higuchi et al confirmed that the self-condensation of 2-hydroxymethylphenol (2-HMP) is kinetically of genuine first-order and the QM hypothesis seems to hold in such a reaction [ 15 ]. However, in their continuous studies on 4-hydroxymethylphenol (4-HMP) [ 16 ], 2,4-dihydroxymethylphenol (2,4-DHMP) [ 17 ] and 2,4,6-trihydroxymethylphenol (2,4,6-THMP) [ 18 ], the condensations appeared to be of fractional order, ranging from 1.1~2.0. Further, the reaction order varied with the change of the NaOH/HMP molar ratio and with the change of the HMP concentration.…”