Understanding the thermal decomposition mechanism of a halogen-free chelated orthoborate-based ionic liquid: a combined computational and experimental study

Abstract

In the last few decades, ionic liquids (ILs) have gained significant attention as lubricants and lubricant additives due to their polar nature, low vapour pressure and tunable physicochemical properties. In this work, quantum chemistry calculations and atomistic Molecular Dynamics (MD) simulations were employed to predict thermal degradation mechanisms of a potential lubricating agent - the tributyloctylphosphonium bis(oxalato)borate ([P4,4,4,8][BOB]) IL. It was found that the onset of decomposition of the studied IL coincides with a cleavage of the B-O bonds in the [BOB](-) anion. Consequently, a series of chemical reactions of the [P4,4,4,8](+) cation with the [BOB](-) anion was triggered yielding alkylboranes, alkenes, trialkylphosphines, CO and CO2. Another ionic system, consisting of [P4,4,4,8][Cl], was also tested for a comparison. Thermogravimetric measurements have shown a higher thermal stability of [P4,4,4,8][BOB] compared to that of [P4,4,4,8][Cl] at least at the initial stage of decomposition, in accord with the presented calculations. Quantum chemical frequency calculations also agreed with the experimental Fourier Transform Infrared (FTIR) spectroscopy results.

Transition anionic complex in trihexyl(tetradecyl)phosphonium-bis(oxalato)borate ionic liquid – revisited

“…A gradual weight loss of tetraalkylphosphonium chlorides is due to a stronger nucleophilicity of the chloride anion initiating de-alkylation reactions 50 and a partial vaporisation of the ILs in the form of coupled ion pairs with an increase in temperature. 51 9 ) before the heat treatment (see Fig. 7 left and Table 2).…”

Non-halogenated Ionic Liquid Dramatically Enhances Tribological Performance of Biodegradable Oils

“…It has been demonstrated for the same OPAG/IL mixture that such an electro-diffusion process is indeed controlled by the surface charge (Hjalmarsson et al, under review). Thermomechanical stresses cause the anions to decompose and it is thought that decomposition starts with the cleavage of a B-O bond, which simulations demonstrate to be energetically most vulnerable (Golets et al, 2016). Boron may contribute to formation of B 2 O 3 and BPO 4 while phosphorus may contribute to formation of phosphates and polyphosphates (Sharma et al, 2016).…”

Dynamic properties of imidazolium orthoborate ionic liquids mixed with polyethylene glycol studied by NMR diffusometry and impedance spectroscopy

“…For the synthesis of [C n C 1 Im][BMB], previously reported method was used and [C 10 C 1 Im][BOB] was synthesized following the method reported by Golets et al . Purification and physicochemical characterization of the synthesized ILs were performed according to the procedure described previously .…”