DFT Study of the Reaction Mechanisms of Carbon Dioxide and its Isoelectronic Molecules CS₂ and OCS Dissolved in Pyrrolidinium and Imidazolium Acetate Ionic Liquids

Abstract

The reaction mechanisms of CO2 and its isoelectronic molecules OCS and CS2 dissolved in N-butyl-N-methylpyrrolidinium acetate and in 1-butyl-3-methylimidazolium acetate were investigated by DFT calculations in "gas phase". The analysis of predicted multistep pathways allowed calculating energies of reaction and energy barriers of the processes. The major role played by the acetate anion in the degradation of the solutes CS2 and OCS as well as in the capture of OCS and CO2 by the imidazolium ring is highlighted. In both ionic liquids, this anion governs the conversion of CS2 into OCS and of OCS into CO2 through interatomic S-O exchanges between the anion and the solutes with formation of thioacetate anions. In imidazolium acetate, the selective capture of CS2 and OCS by the imidazolium ring competes with the S-O exchanges. From the calculated values of the energy barriers a basicity scale of the anions is proposed. The (13)C NMR chemical shifts of the predicted adducts were calculated and agree well with the experimental observations. It is argued that the scenario issued from the calculated pathways is shown qualitatively to be independent from the functionals and basis set used, constitute a valuable tool in the understanding of chemical reactions taking place in liquid phase.

Optical and XPS evidence for the electrochemical generation of an N-heterocyclic carbene and its CS2adduct from the ionic liquid [bmim][PF6]

“…6) of similar imidazolium dithiocarboxylate derivatives. 50,56,[60][61][62] In accordance with this observation, the visible spectrum of 3 recorded in CH 2 Cl 2 shows the presence of two intense absorption bands at 530 nm and 430 nm, as shown in Fig. 3a.…”

Carbonyl Sulfide-Mediated Synthesis of Peptides with Amino Acid Ionic Liquids

“…Based on the previous studies of the mechanism for prebiotic peptide formation, 3,14 two possible pathways were proposed to explain the enhancement effect of OCS on peptide formation using AAILs. In the first mechanism (Scheme 3A), the imidazolium cation assists the OCS-mediated conversion of the anion of AAIL 1 to a C-terminal amino acid thiocarboxylate 2, 15,16 which is oxidized to a dimeric thiocarboxylate 3 in ionic liquid. A protected dipeptide attached to the resin 5 arises by the coupling of resin-bound amino acid 4 with 2.…”

Interaction of N‐Heterocyclic Carbenes and Simple Carbenes with Small Molecules (One to Three Atoms) Excluding Metals: Formation of Covalent C–X Bonds

“…The NHC:CS 2 adducts were prepared bubbling CS 2 through the corresponding NHCs [102,112,[120][121][122][123][124][125], but in a paper, continuous flow technique was used [126], and in another instead NHCs, their dimers (enetetramines) were used [5]. These adducts are useful ligands; very few papers reported another type of reactivity, for instance, one is related to capture of CS 2 [127].…”

“…For carbenes bearing a carbonyl group adjacent to the N atom, reaction with COS lead to thiols; this corresponds to the loss of the more stable CO gas over CS . A DFT study of the mechanism of carbonyl sulfide in imidazolium acetate ionic liquid has been published . A theoretical paper reporting the binding of indirect greenhouse gases CS 2 and COS by NHCs has been published .…”