In the present work, the pyrolysis reaction mechanism of both furfuryl benzoate and furfuryl acetate was evaluated at the M06/6-311++g(d,p) level. The uncommon methylenecyclobutenone compound and either the benzoic or the acetic acid were determined as the products of a multistep process consisting in two [3 + 3] rearrangements and a subsequent hydrogen α-elimination step, through a cyclic 5-membered transition state (TS), being the latter the rate-limiting step for both reactants. Furthermore, a deeper analysis on the basis of the reaction force formalism showed that the TS is formed in two stages: The first one is characterized by the weakening of the C─O bond, and the second one is where the H atom is transferred from the C atom to its nearest O atom. The H─O bond formation was determined to contribute the most to the electronic activity occurring during the TS formation as suggested by a reaction electronic flux analysis. Accordingly, natural bond orbital calculations showed that the most significant changes occur in the charge distribution of the O and H atoms. Finally, a negligible effect of the substituting group on the reaction was determined since similar activation energies were obtained for the pyrolysis of furfuryl benzoate and furfuryl acetate; however, a minor difference was evidenced in the reaction force results. In this sense, the structural contribution to the activation energy is larger than the electronic one for the furfuryl benzoate reaction, wSR 1 > wSR 2, whereas the opposite is observed for the furfuryl acetate reaction, wSR 1 > wSR 2.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry