Mechanism of Base-Catalyzed Resorcinol-Formaldehyde and Phenol-Resorcinol-Formaldehyde Condensation Reactions: A Theoretical Study

Abstract

Abstract:The base-catalyzed resorcinol-formaldehyde condensation reactions were theoretically investigated in this study by employing a quantum chemistry method. The condensation reaction includes two steps: (1) formation of the quinonemethide (QM) intermediate from hydroxymethylresorcinol; (2) Michael addition between the quinonemethide and resorcinol anion. The first step is the rate-determining step. Two mechanisms, unimolecular elimination of the conjugate base (E1cb) and water-aided elimination (WAE), were identified for the formation of QM. The hydroxymethylresorcinol anion produces neutral QM while the dianion produces a quinonemethide anion (QMA). The calculated potential energy barriers suggested that the QMA formation is much more favorable. Although resorcinol-formaldehyde and phenol-formaldehyde condensations share a common mechanism, the former would be faster if the QMA participates in condensations. The potential energy barriers for formation of 2-QM, 4-QM, 6-QM, 2-QMA, and 4-QMA were calculated. The results show that the formations of 6-QM and 4-QMA have relatively lower energy barriers. This rationalized previous experimental observations that the 2,4-(2,6-) and 6,6 -(4,4 -) methylene linkages were dominant, whereas the 2,2 -linkage was almost absent. The resorcinol-phenol-formaldehyde co-condensations were also calculated. The cold-setting characteristic of phenol-resorcinol-formaldehyde co-condensed resin can be attributed to participation of resorcinol quinonemethides in condensations.

Polyvinylpyrrolidone-resorcinol-formaldehyde hydrogel system reinforced with bio-synthesized zinc-oxide for water shut-off in heterogeneous reservoir: An experimental investigation

“…From pictures, it can be deduced that ZnO has a considerable impact on the morphology of PVP-ZnO:RF nanocomposite hydrogels. Nanocomposite hydrogel shows a very dense surface, which indicates that ZnO has significant interaction with PVP & RF in the synthesis of PVP-ZnO:RF hydrogel (Li et al, 2017).…”

Solar-to-hydrogen peroxide energy conversion on resorcinol-formaldehyde resin photocatalysts prepared by acid-catalysed polycondensation

“…hydrothermal process removes the -OH groups from the methylols, leading to the formation of highly electrophilic quinone methides. 31,32 The nucleophilic addition of the methylols to the quinone methides 33 produces quinoid forms, which are -conjugated with benzenoid forms. These reactions 8 create a highly crosslinked D-A architecture (Fig.…”

The Fundamental and Underrated Role of the Base Electrolyte in the Polymerization Mechanism. The Resorcinol Case Study

“… 14 − 17 In fact, resorcinol polymerization must proceed through the dissociation of one (or two) hydrogen atom, as it is also assumed in resorcinol condensation reactions. 18 This is the case for other complex reactive systems, spanning from photochemistry to electrochemistry, where the charge transfer elementary act is coupled with the proton dissociation. 19 − 22 In our study we focused on the initial reaction steps leading to the formation of dimers.…”