Thermal reaction of the ionic liquid 1,2-dimethyl-(3-aminoethyl) imidazolium tetrafluoroborate: a kinetic and theoretical study

Abstract

Since the thermal stabilities of ionic liquids (ILs) are of significance for their application, an amine-functionalized IL 1,2-dimethyl-(3-aminoethyl) imidazolium tetrafluoroborate [aEMMIM][BF4] was chosen to study thermal decomposition mechanisms via the methods of FT-IR, (1)H NMR, TGA, TGA-MS and density functional theory (DFT) calculations. Theoretical and experimental results indicated that amine-functionalization reduces the thermal stability of [aEMMIM][BF4] compared to its non-functionalized counterpart. Moreover, we found that [aEMMIM][BF4] follows a unimolecular nucleophilic substitution (SN1) decomposition (98.8 %), whereas the bimolecular nucleophilic substitution (SN2) decomposition (1.2 %) is unfavorable. The SN1 and SN2 reactions were fully optimized at B3LYP/6-311++G(d,p) level, and the energies of reactant (R), intermediates (IM), transition state (TS) and product (P) were obtained and analyzed by reaction mechanism. The energy of the intermediate is higher than that of the reactants by 18.92 kJ mol(-1), and the energy of the TS is higher than that of the IM by 155.23 kJ mol(-1). This result indicates that the IM are also more stable than the P2 product, thus the reaction is endothermic. The chemical nature of the covalent and hydrogen bonds was analyzed by vibrational modes analysis (VMA), nature bond orbital (NBO) and the theory of atoms in molecules (AIM). Graphical Abstract Proposed thermal decomposition of [aEMMIM][BF4] via unimolecular ( SN1) and bimolecular( SN2) nucleophilic substitution mechanisms. The electrostatic potential surface (ESP) of the transition state illustrates that hydrogen bonds are generated when [BF4](-) is close to [aEMMIM](+), and SN1 decomposition is much favorable than SN2 decomposition.

Green synthesis of 1-phenyl-1-ortho-xylene ethane in IL and reaction mechanism

“…To avoid pollution a more environmentally friendly catalyst is desired. 2,3 Room temperature ionic liquid (IL) systems have many unique properties such as a very large liquid temperature range, and they can be made task-specic for certain applications, 4 which include use as solvents in chemical synthesis and catalysis [5][6][7][8][9][10][11] and separation technology, 12,13 as electrolytes in electrochemical devices, [14][15][16] and as lubricants or as heat-transfer uids. 17 In addition, there is a huge range of possible combinations of cations and anions, which contribute to the design of ILs.…”