Avaliação de modelos cinéticos para dissociação unimolecular de furano

Abstract

The search for renewable fuels as an alternative to fossil fuels directs global scientific and technological research increasingly toward the study of biofuels and other renewable sources, thus, furans compose a family with promising potential. All the reasons for the interest for the study of these substances are justified by recent works proposing large-scale processes for furan production and its substituted derivatives such as methyl furan and 2,5-dimethylfuran from biomass. In this work the kinetic models of unimolecular dissociation, specifically furan, are evaluated. Geometry optimization calculations were made for stationary points and transition states were found by identifying the imaginary vibrational frequency that characterize the desired movements for the occurrence of the reaction. Also, reaction paths were calculated using the intrinsic Reaction Coordinate (IRC) algorithm. All these calculations were performed with the aid of the Density Functional Theory (DFT) with the M06-2X functional and the aug-cc-pVDZ basis set. In sequence, rate coefficients were calculated by the variational method. In order to obtain rate coefficients in larger sets of basis, aug-cc-pVTZ and aug-cc-pVQZ, an interpolation of the previously obtained reaction path data was performed. Once kinetic data were obtained for the dissociations and their respective reversible reactions, experimental works were simulated using the kintecus® software under different temperature, pressure and concentration values. In short, five different reaction paths were proposed, each of them presenting a different initial barrier characterized by a specific saddle point for each case. These mechanisms were initiated by several migrations of H, leading to different products. The energy values obtained at the M06-2X level are in accordance with CASPT2 and G2 (MP2) results previously reported in the literature. Lastly, the reaction paths were described with the proposal of new stationary points located in the reaction paths that compose the unimolecular decomposition mechanism of furan, justifying the products (and their proportions) experimentally observed.