Development of Low Melting Ionic Liquids using Eutectic Mixtures of Imidazolium and Pyrazolium Ionic Liquids

Abstract

Phase diagram of the binary ionic liquid 1-ethyl-3- methylimidazolium hexafluorophosphate ([emim][PF6]) - 1- ethyl-2-methylpyrazolium hexafluorophosphate ([empz][PF6]), was determined. The binary system shows a eutectic at 23oC, (which is 38oC below the melting point of the lower melting salt [emim][PF6]), and at the molar composition [emim][PF6]: [empz][PF6] ≈ 47:53. Therefore using the eutectic method a low melting ionic liquid was formed with single salts that contain only small alkyl groups on the cations. At ambient temperature the ionic conductivity of the eutectic mixture is comparable to that of a low melting single salt such as, 1-n-butyl-3- methylimidazolium hexafluorophosphate ([bmim][PF6]), but at higher temperature (e.g. 90oC) the conductivity of the eutectic mixture is 20% higher. This method allows the preparation of purer ionic liquids since the two single salts can be purified by recrystallization, before they are mixed to form the binary system which is a liquid at ambient temperature. Hence the ionic liquids produced by the eutectic method have the potential for finding wider range of applications compared with low melting ionic liquids (single salts) containing longer alkyl groups prepared by the conventional method.

Mixing cations with different alkyl chain lengths markedly depresses the melting point in deep eutectic solvents formed from alkylammonium bromide salts and urea

“…17 The melting point of 1 : 1 EABr : BABr is 80 1C, much lower than either pure salt, and the endotherm is broader. Similar effects have been noted for mixtures of ionic liquids, 18 and attributed to the different sized cations frustrating ion packing. 19 Fig.…”

Properties modification by eutectic formation in mixtures of ionic liquids

“…The crystallised product was ltered and washed with a new portion of ethyl acetate, dried in the rotary evaporator and later under high vacuum. The absence of remaining starting materials or other impurities in the nal product, a white crystalline powder, was checked by 1 H and 13 C NMR spectroscopy. The water content was found to be 0.0010 in mass fraction.…”

“…If the mixed ionic liquids form a eutectic, then the melting temperature of the resulting mixture will be lower than that of the parent compounds, enabling its use in liquid state over a broader temperature range including lower operation temperatures. 5,12 Despite this appealing effect, few articles in the literature have been devoted, to date, to the thermodynamic exploration of eutectic mixtures of ionic liquids; [12][13][14][15] with a couple of articles investigating the application of binary mixtures of ionic liquids as catalysts or reaction media, 16,17 and of melts based on eutectic mixtures of ionic liquids as electrolytes in dye-sensitised solar cells. 18,19 The examples reported focus almost exclusively in mixtures of imidazolium-based ionic liquids.…”

Responsive Ionogel Surface with Renewable Antibiofouling Properties

“…The IL mixtures with different compositions show two distinct melting temperatures in differential scanning calorimetry (DSC, Figure b and Figure S1, Supporting Information). This phenomenon is different from that observed in eutectic mixtures of IL . We regard it as a result of the mismatch between the cations due to the difference in length of 1‐alkyl chains.…”