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

Mitani, Ryusuke; Yamamoto, Hidetoshi; Sumimoto, Michinori

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.

RING-opening reactions; PHENOXIDES; DENSITY functional theory; ACTIVATION energy; SCISSION (Chemistry)

Molecules, 2023, Vol 28, Issue 2, p694

1420-3049

Academic Journal

10.3390/molecules28020694