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. 2023 Jan 10;28(2):694.
doi: 10.3390/molecules28020694.

Theoretical Study of the Reaction Mechanism of Phenol-Epoxy Ring-Opening Reaction Using a Latent Hardening Accelerator and a Reactivity Evaluation by Substituents

Ryusuke Mitani  1 , Hidetoshi Yamamoto  1 , Michinori Sumimoto  1
Affiliations

Theoretical Study of the Reaction Mechanism of Phenol-Epoxy Ring-Opening Reaction Using a Latent Hardening Accelerator and a Reactivity Evaluation by Substituents

Ryusuke Mitani et al. Molecules. .

Abstract

The mechanism of the phenol-epoxide ring-opening reaction using tetraphenylphosphonium-tetraphenylborate (TPP-K) was investigated using the density functional theory (DFT) method. The reaction was initiated by breaking the P-B bond of TPP-K. The generated tetraphenylborate (TetraPB-) reacted with phenol to form a phenoxide ion, which combined with tetraphenylphosphonium (TPP+) to produce the active species, i.e., tetraphenylphosphonium phenolate (TPP-OPh). The phenoxide ion in TPP-OPh nucleophilically attacked the epoxide. Simultaneously, the H atom in the phenolic OH group moved to the O atom of the ring-opened epoxide. The formed phenoxide ion bound to TPP+ again, and TPP-OPh was regenerated. The rate-determining steps in the reaction were the cleavage of the P-B bond and the triphenylborane-forming reaction. The free energies of activation were calculated to be 36.3 and 36.1 kcal/mol, respectively. It is also suggested that these values in the rate-determining steps could be manipulated by substituents introduced on the Ph group of TetraPB-. Based on these results, it is possible to construct new design guidelines for latent hardening accelerators such as TPP-K.

Keywords: density functional theory; latent hardening accelerator; phenol–epoxy ring-opening reaction; tetraphenylphosphonium-tetraphenylborate.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Reaction mechanism proposed by experimental chemists.
Figure 1
Figure 1
Geometry and free energy changes in the triphenylborane-forming reaction. The bond lengths are in Å. Relative free energies (kcal/mol) to REA_B0 are in parentheses.
Figure 2
Figure 2
Free energy changes in the tetraphenylphosphonium phenolate-forming reaction. Relative free energies (kcal/mol) to REA_P1 are in parentheses.
Figure 3
Figure 3
Geometry and free energy changes in the phenol–epoxy ring-opening reaction using TPP-OPh. The bond lengths are in Å. Relative free energies (kcal/mol) to REA_P2 are in parentheses.
Figure 4
Figure 4
Geometry and free energy changes in the triphenylborate-forming reaction. The bond lengths are in Å. Relative free energies (kcal/mol) to REA_B1 are in parentheses.
Figure 5
Figure 5
Free energy changes in phenol–epoxide ring-opening reaction using TPP-K. Relative free energies (kcal/mol) to REA_T and REA_B0 are in parentheses.
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