Thermomorphic Behavior of the Ionic Liquids [C₄mim][FeCl₄] and [C₁₂mim][FeCl₄]

Abstract

The iron-containing ionic liquids 1-butyl-3-methylimidazolium tetrachloroferrate(III) [C(4)mim][FeCl(4)] and 1-dodecyl-3-methylimidazolium tetrachloroferrate(III) [C(12)mim][FeCl(4)] exhibit a thermally induced demixing with water (thermomorphism). The phase separation temperature varies with IL weight fraction in water and can be tuned between 100 °C and room temperature. The reversible lower critical solution temperature (LCST) is only observed at IL weight fractions below ca. 35 % in water. UV/Vis, IR, and Raman spectroscopy along with elemental analysis prove that the yellow-brown liquid phase recovered after phase separation is the starting IL [C(4)mim][FeCl(4)] and [C(12)mim][FeCl(4)], respectively. Photometry and ICP-OES show that about 40 % of iron remains in the water phase upon phase separation. Although the process is thus not very efficient at the moment, the current approach is the first example of an LCST behavior of a metal-containing IL and therefore, although still inefficient, a prototype for catalyst removal or metal extraction.

Extraction of Metals with ABS

“…Although there is, to the best of our knowledge, only a single paper [20] falling in this category, we found the results obtained of high interest. In particular, the number of compounds is limited to two, water and one IL, but nevertheless contains everything needed for metal extraction.…”

“…Examples with both cationic and anionic components being metallic entities can also be found [59]. For most of these metalcontaining ILs (Mn, Fe, Co, Gd, Dy…), magnetic properties are mostly studied and very limited knowledge is found on their thermomorphic behavior in the literature, the only example being for H 2 O&[C 1 C 4 im + ][FeCl 4 -] (glass transition of the IL at T = -88 °C [56]) which displays a LCST behavior [20,60]. For 25 wt% of IL, the change from mono-to biphasic state occurs at T c = 50 °C, while at 20 wt% of IL, changes occurs at T c = 90 °C.…”

“…For 25 wt% of IL, the change from mono-to biphasic state occurs at T c = 50 °C, while at 20 wt% of IL, changes occurs at T c = 90 °C. Below 20 wt% of IL, T is above 100°C and above 30 wt%, T c is below 10 °C so the authors were not able to determine the complete miscibility curve [20]. .…”

Structural Effects on the Physico‐Chemical and Catalytic Properties of Acidic Ionic Liquids: An Overview

“…It has recently been shown, for example, that these mixtures display significant thermomorphism (i.e., thermally induced demixing). [33] With regard to the magnetic properties, although iron-based ILs are simply paramagnetic, they still respond to applied external magnetic fields. Droplets of the [C 10 mim][FeCl 4 ] and [PR 4 ][FeCl 4 ] salts can be added to water, with which they are at least initially immiscible (phosphonium salts are always immiscible) and can then be quite easily manipulated through the application of an external strong magnetic field.…”

Magnetic ionic liquid assisted single‐drop microextraction of ascorbic acid before its voltammetric determination

“…Most of the MILs used in the extraction procedures contain FeCl 4 − anion. However, FeCl 4 − hydrolyzes when exposed to aqueous solutions, even at ambient temperature [23,24]. In contrast, hydrophobic MILs containing MnCl 4 2− anion are less prone to undergo hydrolysis in aqueous solutions.…”