Abstract
Non-halogenated boron-based ionic liquids (ILs) composed of phosphonium cations and chelated orthoborate anions have high hydrolytic stability, low melting point and exceptional properties for various applications. This study is focused on ILs with the same type of cation, trihexyltetradecylphosphonium ([P6,6,6,14]+), and two orthoborate anions, such as bis(salicylato)borate ([BScB]−) and bis(oxalato)borate ([BOB]−). We compare the results of this study with our previous studies on ILs with bis(mandelato)borate ([BMB]−) and a variety of different cations (tetraalkylphosphonium, dialkylpyrrolidinium and dialkylimidazolium). The ion dynamics and phase behavior of these ILs is studied using 1H and 11B pulsed-field-gradient (PFG) NMR. PFG NMR is demonstrated to be a useful tool to elucidate the dynamics of ions in this class of phosphonium orthoborate ILs. In particular, the applicability of 11B PFG NMR for studying anions without 1H, such as [BOB]−, and the limitations of this technique to measure self-diffusion of ions in ILs are demonstrated and discussed in detail for the first time.
Highlights
Ionic liquids (ILs) are salts that are in a liquid state at temperatures below 100◦C
We have previously found that this IL exists in either one or two fluidic “phases” in the temperature range from 20 to 100◦C
Diffusion of ions is measured in two selected tetraalkylphosphonium orthoborate based ILs with the trihexyl(tetradecyl)phosphonium cation in combination with two different orthoborate anions having different chemical groups in the temperature range 293–363 K using 1H and 11B NMR data
Summary
Ionic liquids (ILs) are salts that are in a liquid state at temperatures below 100◦C. Some ILs are liquids under normal conditions and, are usually called room temperature ionic liquids (RTILs). ILs possess many unique physicochemical properties such as high polarity, non-volatility, high thermal stability, high ionic conductivity, and a wide liquid range, among other properties. ILs can be chemically modified and tailored for a wide range of industrial applications (Plechkova and Seddon, 2008; Hallett and Welton, 2011). The majority of well-studied ILs consist of halogenated anions such as tetrafluoroborate [BF4]− and hexafluorophosphate [PF6]−, and are sensitive to moisture, which limits their utility in many industrial applications. Development of non-halogenated and hydrolytically stable ILs for different industrial applications might be an ultimate goal to avoid environmental and health-related issues associated
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