title: 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.
authors.affiliation: Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden. aatto.laaksonen@mmk.su.se mikhail.golets@yahoo.se.
authors.forename: M
authors.initials: M
authors.lastname: Golets
authors.affiliation: Chemistry of Interfaces, Luleå University of Technology, S-97187, Luleå, Sweden.
authors.forename: M R
authors.initials: MR
authors.lastname: Shimpi
authors.affiliation: Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden and System and Component Design, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
authors.forename: Y-L
authors.initials: YL
authors.lastname: Wang
authors.affiliation: Chemistry of Interfaces, Luleå University of Technology, S-97187, Luleå, Sweden.
authors.forename: O N
authors.initials: ON
authors.lastname: Antzutkin
authors.affiliation: System and Component Design, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden and Mechanical Construction and Production, Ghent University, B-9000 Ghent, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Glavatskih
authors.affiliation: Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden. aatto.laaksonen@mmk.su.se mikhail.golets@yahoo.se and Stellenbosch Institute of Advanced Study (STIAS), Wallenberg Research Centre, Stellenbosch University, Marais Street, Stellenbosch 7600, South Africa.
authors.forename: A
authors.initials: A
authors.lastname: Laaksonen