The trialkylsulfonium cation holds promise to capture carbon dioxide: In-silico evidence toward a novel scavenger

Abstract

The concentration of carbon dioxide (CO2) in the Earth’s atmosphere is linked to the acute problem of global warming. For the first time, we herein introduce trialkylsulfonium aprotic ionic liquids (ILs) as a group of seemingly highly capacitive CO2 scavengers. We advocate the viability of the new sorbents by the reaction profiles recorded by means of hybrid density functional theory. All stages constituting CO2 chemisorption, such as the ethyldimethylsulfonium [S211] cation deprotonation, [S211]-ylide carboxylation at the α-methylene group, and aprotic anion carboxamidation have been explored. The [S211]-ylide formation reaction is thermochemically forbidden but its cost is affordable. The energetic cost ranges from a tiny number of +14 kJ/mol for [S211] indazolide to a mediocre value of +50 kJ/mol for [S211] 1,2,4–triazolide. The barriers corresponding to the sulfonium-based cation deprotonation range from +39 kJ/mol for benzimidazolide to +60 kJ/mol for 1,2,4-triazolide. The energy loss during the ylide intermediate formation is strongly compensated for by the subsequent sulfonium ylide carboxylation. The energetic gain is weakly dependent on the nature of the heterocyclic aprotic anion (AHA) being –99 to –110 kJ/mol for different ionic species studied. The AHAs additionally participate in CO2 capture following the route of carboxamidation thanks to their nitrogen sites. The most thermochemically favorable carbamate forms out of [S211] indazolide, –68 kJ/mol. The steric and covalent barriers associated with these reactions are of the order of thermal motion energy, whereas a specific chemical structure of AHA engenders marginal differences. The rationalization of the energy reaction profiles is given in terms of partial atomic charges, geometrical peculiarities, steric barriers, imaginary vibrational frequencies, and related descriptors. The reported computational results favor trials of the sulfonium-based ILs for CO2 chemisorption both thermochemically and kinetically.