Novel Electrochemical Studies of Ionic Liquids

Abstract

Room-temperature ionic liquids (ILs) have been proposed as alternative solvents for organic synthesis, separations, and electrochemical applications. Here, we report studies that probe the electrochemical and solvation properties of a tetraalkylammonium (methyltributylammonium bis(trifluoromethylsulfon)imide, M3BNIm) and an imidazolium (1-butyl-3-methylimidazolium hexafluorophosphate, BMIPF6) based ionic liquid. It is demonstrated that despite impurities, the cathodic limit at a Pt electrode is enhanced for the tetraalkylammonium-based IL. Electrogenerated chemiluminescence of tris(2,2‘-bipyrindinyl)ruthenium (Ru(bpy)3 2+) was observed in both ionic liquids, and differences in the response were interpreted in terms of the solvent reactivity and polarity. As ILs have been proposed as alternatives to organic solvents in extraction processes, an understanding of the relative lipophilicity of the IL ions and the equilibrium potential difference established across the IL/water interface is of fundamental relevance. Here, electrochemical measurements at a conventionally polarized liquid−liquid interface (water/1,2-dichloroethane) were used to determine the relative lipophilicity of the IL constituent ions. From formal ion transfer potential values ( ) obtained, the standard ionic partition coefficients could be estimated. The polarizability of the neat ionic liquid/water interface was investigated. From these studies, it can be seen that BMIPF6 is hydrophilic while M3BNIm is moderately hydrophobic. The significance of the potential difference established across the IL/water interface is discussed.

Spotlight on ionic liquids

“…On the other hand, neutral solutes are not as strongly coupled to their neighbors and may sample less polar, lower friction nanoenvironments, resulting in faster diffusion. The effects can also occur in the opposite directionQuinn et al 133 predicted viscosities 3.4 times higher than were observed for two ILs based on electrochemically obtained diffusion coefficients for the divalent Ru͑bpy͒ 2 2+ cation. Pulse radiolysis studies have shown that the diffusionlimited reactions of ͑anionic͒ solvated electrons with aromatic molecules in ILs are slower that those of neutral hydrogen atoms with the same substrates, reversing the trend observed in regular solvents.…”

Construction of an Optical Sensor for the Determination of Ascorbic Acid Using Ionic Liquids as Modifier

“…The ILs have, in fact, been successfully used in many applications, including replacing traditional organic solvents in organic and inorganic syntheses, solvent extractions, liquid-liquid extractions, and electrochemical reactions as well as a medium to enhance the sensitivity of thermal-lens measurements. [23][24][25][26] A new optical sensor was reported for the determination of cyanide ion and the application of ionic liquid, as a modifier, has been introduced for constructing optical sensors. 27 In this research, an optical sensor was reported to be as a rapid, routine and selective indirect spectrophotometric determination of ascorbic acid based on its reducing ability.…”

Array of water|room temperature ionic liquid micro-interfaces

“…Recently, ion transfer at the water|room temperature ionic liquid (W|RTIL) interface has attracted increasing attention, since the first report by Quinn et al [5]. In particular, the group of Kakiuchi has been very active [6][7][8] since their pioneering work in 2003 [9], and the first review paper on this topic was published recently [10].…”