  The concentration of carbon dioxide (CO2) in the Earth 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 alpha-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 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.
