Effect of Isomerism on the Liquid–Liquid Phase Behavior of Mixtures of 1-Alkyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)amide Ionic Liquids with Heptanol

Abstract

Systematic investigations on the liquid–liquid phase behavior of binary mixtures of ionic liquids (IL) of the type 1-alkyl-3-methylimidazolium bis­((trifluoromethyl)­sulfonyl)­amide (C x mimNTf2, x = 2, 4, 6, 8, and 10) with n-heptanol and its branched isomers 3-ethyl-3-pentanol and 2,4-dimethyl-3-pentanol have been performed. The phase diagrams were determined at atmospheric pressure in the temperature range (T) of 263–448 K by applying the cloud point method. The phase diagrams are analyzed in terms of well-established numerical concepts based on Ising criticality. The results are discussed, and trends and explanations for the shifts of the range of solubility are given. The systems show partial miscibility with upper critical solution temperatures. Comparing the solutions in branched alcohols with those in the linear isomer, the critical solution points are found to be remarkably shifted toward higher temperatures and lower IL contents. The trend becomes more pronounced for ILs with shorter alkyl side chains where also a change of the shape of the phase diagrams is observed.

Revisiting the Liquid–Liquid Phase Behavior of n-Alkanes and Ethanol

“…Chemical stability is sometimes a problem for measurements of phase diagrams as well. 51,57,60,61 In the present study, no signs of decomposition or chemical reaction were observed in any of the systems even at the highest temperatures considered.…”

“…The phase diagrams are determined by combining the synthetic method with the cloud point method. While the procedure of sample preparation was improved during the past years, ,, the reader is referred to the most recent paper on this topic, which describes the actual state of the art in sample preparation for LLE mixtures. In brief, by using computer-assisted syringe pumps for sample sizes of 1–2 g, an overall uncertainty ( k = 2) in the mole fraction of U ( x IL ) = ± 10 –4 is achieved.…”

“…For the sake of data integrity, samples of larger sizes were also checked and were handled in suitable Duran glass bottles using a cap and a sealing system with the same specifications (Duran Group, Mainz, Germany), each again under a protective argon atmosphere. The whole assembly enables easy handling in a temperature range of T = 225–425 K. Therefore, there was no need to leave the standard procedure of cloud point detection described in the previous studies for temperatures above 370 K. , …”

“…For the sake of data integrity, samples of larger sizes were also checked and were handled in suitable Duran glass bottles using a cap and a sealing system with the same specifications (Duran Group, Mainz, Germany), each again under a protective argon atmosphere. The whole assembly enables easy handling in a temperature range of T = 225−425 K. Therefore, there was no need to leave the standard procedure of cloud point detection described in the previous studies for temperatures above 370 K. 40,51 To reach temperatures far below room temperature (T = 230−265 K), a transparent liquid bath, equipped with insulation and double-glazed windows (volume of 20 L) filled with an ethylene glycol−water mixture (60:40 v/v), was used. 63 14, 62,64 16, 62,64,65 and 18.…”

“…More recently, organic molten salts melting at low temperature termed as ionic liquids gained increasing attention. − Subsequently, binary mixtures of this new class of solvents with classical solutes became a popular topic now leading to research and application of deep eutectic solvents (DES). − Nevertheless, the background knowledge regarding these systems is still insufficient. Systematic studies varying selected properties of the components are rare: among the few examples, the family of 1-alkyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­amide– n -alkyl alcohol mixtures was comprehensively characterized. − Unfortunately, most of the investigated systems show such a high number of degrees of freedom that a detailed understanding of solubility properties of the mixtures is still challenging or even impossible. − Structure-property relationships approaches such as group contribution methods or empirical equations of high complexity often do not yield sufficient congruent results, which could serve as a reference for theory. − A self-containing description, which is in agreement with theoretical consistency, is still a challenging problem.…”