Estudo computacional da reação entre o íon Alilo e ésteres de enxofre análogos em fase gasosa: mecanismos e seletividade

Abstract

Sulfur esters are part of the group of sulfate aerosol precursors, and it is important to study their interactions with some nucleophiles, especially those in the gas phase, since this is the phase in which they are found in nature. From this perspective, sulfur ester reactions in the gas phase comprise a chemical reaction system of important interest, since environmental research has proposed the controlled release of these substrates as a strategy to cope with climate change. In this context, this work aimed to study mechanisms for reaction systems with sulfur esters in the gas phase through electronic structure methods. Thus, this research was carried out at the MP2/6-31+G(d,p) level for the optimization calculations of thestationary points of the reaction systems. Through the calculations performed, values of electronic energies and zero-point energies were obtained, later corrected with the aug-ccpVNZ basis set (n=D; T), which allowed relating them and determining the potential energy values for each of the reaction pathways presented in the systems. The reaction mechanisms analyzed were second-order nucleophilic substitution with attack on carbon and sulfur, second-order elimination with dissociation on carbon and proton transfer. Thus, through the kinetic parameters applied to the statistical theory, a predominant selectivity of 100% was observed for the second-order substitution pathway on carbon in the (MeO)2SO2 system and a ratio of 69:31 for the PT:SN2@C of the (MeO)MeSO2 system, kinetically controlled and in experimental agreement. However, the (MeO)2SO system did not show agreement with the experiments that suggest sulfur as the reactive center, with no explanation by the Transition State Theory. Thus, it is expected to have contributed to the study of the reactivity of sulfur esters in a quantitative manner and determining the reactive centers of these species based on the energies of the reaction barriers and proposing molecular dynamics analyses for some systems.