Electron transfer in N-butylpyridinium tetrafluoroborate ionic liquid by pulse radiolysis

Abstract

The radiolysis behavior of neat pyridinium ionic liquids (ILs) and their aqueous solutions was investigated using nanosecond pulse radiolysis techniques. Radiolysis of the ionic liquids, such as N-butylpyridinium tetrafluoroborate (BuPyBF 4 ), resulted in the formation of solvated electrons and organic radicals. Solvated electrons reacted with the pyridinium moiety to produce a pyridinyl radical, which can transfer electrons to various acceptors. The electron-transfer rate constants of the solvent-derived butylpyridinyl radicals in BuPyBF 4 and in several compounds (for example, duroquinone, 4,4′-pyridine, benzophenone, and 1,1′-dimethyl-4,4′-bypyridinium dichloride) (k of the order 10 8 L/(mol s) were lower than those measured in water and in i-PrOH but were significantly higher than the diffusion-controlled rate constants estimated based on viscosity. The electron-transfer rate constants in neat BuPyBF 4 were one order of magnitude faster than the diffusion-controlled values. This finding suggests that BuPyBF 4 acts not only as solvent but also as active solute, such as in solvent-mediated reactions. These reactions result in electrons reaching their final destinations via intervening pyridinium groups without requiring the diffusion of a specific radical. In recent years, ionic liquids (ILs) have become the most studied class of solvents and are considered valid potential substitutes of many volatile organic solvents [1][2][3]. ILs are salts and thus are ionic compounds in liquid form at or near room temperature. ILs exhibit several unique thermophysical properties owing to their asymmetrical structures and the charge dispersion of their organic and inorganic ions. These compounds do not evaporate at ambient temperature and have relatively high thermal stability, high ionic conductivity, and large liquid temperature range. ILs also demonstrate excellent solvent quality for many types of compounds. Traditional methods of chemical kinetics must be applied to the study of IL chemical reactivity to exploit properly the potential of these solvents. In this work, pulse radiolysis techniques were used to observe the electron-transfer reactivity of N-butylpyridinium tetrafluoroborate (BuPyBF 4 ) ILs with several transient species. Pulse radiolysis is a technique where samples are irradiated using a laser-generated beam of high-energy electrons and the species (electron, radicals, cations, etc.) are studied through their absorption spectra [4]. This technique is useful for studying reaction rates, particularly for very fast reactions such as redox reactions and reactions that contain short-lived species. Neta and co-workers [5,6] compared the reaction rate constants of ILs with those of traditional solvents (acetonitrile and alcohol) to determine the stability of ILs as alternative reaction solvents for specific reactions. They studied reaction kinetics in imidazolium salts and in methyltributylammonium bis (trifluoromethylsulfonyl)imide [7][8][9]. However, to the best of our knowledge, only a few studies focused on t...

Synthesis, characterization and theoretical studies on novel organic–inorganic hybrid ion–gel polymer thin films from a γ-Fe2O3doped polyvinylpyrrolidone–N-butylpyridinium tetrafluoroborate composite via intramolecular thermal polymerization

“…35 Earlier, the studies on ET process in bpy[BF 4 ] by pulse radiolysis pointed out that the IL not only acts as solvent but also as active solute in solvent-mediated reactions, while the BF 4 À in bpy[BF 4 ] were not active and did not react with solvated electrons. 36 Other observations from laser ash photolysis (LFP) studies suggest that solvent mediation increases both rates and efficiencies for ET processes in pyridinium based ILs. 30 As a polymer dopant, bpy [BF 4 ] which has low viscosity can signicantly enhance the room temperature conductivity of IL-polymer composites.…”

Photochemical Reaction Kinetics of Duroquinone in a Mixture of Ionic Liquid [BPy][BF₄] and Acetonitrile

“…美国马里兰大学 Vieira 和 Falvey 10 比较研究了咪 唑和吡啶离子液体作为溶剂对电子传递过程的调 控作用. 国内相关研究机构也相继开展了离子液体 中的脉冲辐解与激光光解研究, [16][17][18][19] 着重考查离子液 体本身的激发行为. 16,17 由于吡啶及其衍生物在染料 敏化太阳能电池领域中的潜在应用价值, 20,21…”