Ab Initio MP2 and DFT Study of the Thermal Syn Elimination Reaction in Ethyl Formate

Abstract

The thermal elimination reaction that appears in some polycarbonates has been studied by density functional theory (DFT) and ab initio methods of different levels. This work has been focused in the elimination process of ethyl formate, as a good model of this kind of reaction. Different minima and the transition state have been found to characterize the thermal elimination reaction, and the activation energy has been obtained. In this study, we have used different methods to calculate the contribution of the correlation energy; different basis sets were also employed. This will allow us to perform an analysis of the influence of the applied method in the obtained results to study the thermal elimination. The lengthening of the bonds has also been analyzed to shown how concerted the thermal elimination is in the ethyl formate. Three minima have been found for the ethyl formate, two of them are very close and the third is higher in energy. In general, the DFT method with a B3LYP functional gives a less concerted reaction. A nonplanar transition state is predicted by most of the methods used.

Experimental and RRKM Investigations on the Degradation of Ethyl Formate

“…(48.1 kcal mol −1 , flow tube study below 700 K), Saito et al . (48.5 kcal mol −1 , laser absorption of ethylene formation) and Hermida‐Ramon et al . (49.1 kcal mol −1 , theoretical studies) seem to be a bit higher than the measured one in the present study.…”

“…The measured and computed (RRKM) branching ratios for the formation of ethylene are 84.2% and 98% respectively at 1258 K. This deviation is attributed to the difference in the measured activation energy (42.9 ± 2.2 kcal mol −1 ) and the computed (53.4 kcal mol −1 ) one in this study. However, the computed rate coefficients are in good agreement with reported values and also with experimentally measured one within the limits of experimental uncertainty.…”

“…using shock tube in the temperatures between 1000 and 1300 K. They have observed formation of ethylene using time resolved absorption at 174.5 nm. Hermida‐Ramon et al . studied the formation of ethylene and formic acid from EF using B3LYP/6‐31G** and MP4SDTQ/aug‐cc‐pVDZ//MP2/aug‐cc‐pVDZ levels of theory.…”

Theoretical and Shock Tube Study of the Rate Constants for Hydrogen Abstraction Reactions of Ethyl Formate

“…decomposition experiments of EF at 500-700 K and discovered the principal decomposition pathway EF → C 2 H 4 + HCOOH. This finding was further confirmed by Blades 15,16 using a flow reactor at 830-903 K and Balaganesh et al 17 using a shock tube at 909-1258 K. This dominant EF unimolecular reaction was theoretically studied by Hermida-Ramon et al 18 with the ab initio and DFT methods at different levels of theory. Ren et al 19 recently reported the concentration time-histories of CO, CO 2 , and H 2 O during the pyrolysis of EF in a shock tube, and performed detailed chemical kinetic modeling analysis using the Westbrook et al mechanism.…”

“…We observed that the energies for TSc differ by ~1.0 kcal/mol between the CCSD(T)/CBS(D-T)//M06/cc-pVTZ and CCSD(T)/CBS(D-T)//M06/6-31G(d,p) levels. A higher basis set provides more accurate geometries for TSs18 and…”