Novel DMF-mediated cyclic intermediates facilitating the epoxidation of dicyclopentadiene over a Ti-BEA/H2O2 System

Abstract

The Ti-BEA/H2O2 system has been demonstrated to be capable of producing dicyclopentadiene dioxide in an efficient and environmentally friendly manner. The reaction is catalyzed by Ti-BEA zeolites, which facilitate the formation of Ti-η1(OOH) species in the presence of a solvent and hydrogen peroxide. This intermediate is subsequently converted into Ti-η2(OOH) species. The more stable Ti-η2(OOH) species is more conducive to the epoxidation reaction, and inhibiting the deep reaction of epoxidation products. In this study, the solvent effect of N,N-dimethylformamide (DMF) was employed to regulate the distribution of active intermediates. The material was characterised using in Ultraviolet-visible spectroscopy (UV-Vis) and in situ 13C MAS NMR spectroscopy, and the results were combined with density functional theory (DFT) calculations. It was discovered that the O atoms of DMF are capable of coordinating with the active Ti(IV) of Ti-BEA zeolites. Afterwards, DMF reacted with Ti-OOH to obtain a novel Ti-η1(OOH)-DMF species. This species is characterised by its ability to spontaneously convert to the Ti-η2(OOH) species. The energy required for DMF to engage in the active transition state formation process is significantly less than that of protonic solvents. The experimental results demonstrated that the use of DMF as a solvent resulted in an increased conversion of DCPD, reaching 99.9%. The selectivity of other products is effectively eliminated. A comparison of different amide solvents revealed that the interaction force of DMF with Ti(IV) was found to be greater than that of N-methylformamide (NMF), as determined by crystal orbital hamilton population (COHP) calculations. The catalytic effect was observed to be optimal when DMF was utilized as a solvent. These findings have the potential to enhance the comprehension of epoxidation reactions and provide a theoretical foundation for guiding the production of epoxidation products.