Building Blocks for Ionic Liquids: Vapor Pressures and Vaporization Enthalpies of N-Functionalized Imidazoles with Branched and Cycloalkyl Substituents

Abstract

The imidazole structure offers a versatile means of developing molecules with controlled/tunable physicochemical properties that have significant utility in many applications and can be further derivatized to form ionic liquids. In the literature, the vast majority of studies on structure−property relationships in these types of molecules are devoted to linear (e.g., n-alkyl) substituents. However, imidazoles with branched or cycloalkyl groups are equally accessible through convenient synthetic methods − yet there are essentially no reports on the physical properties of such compounds in the literature. Here, the absolute vapor pressures of branched and cycloalkyl derivatives of imidazole have been determined as a function of temperature by the transpiration method. The standard molar enthalpies of vaporization were derived from the temperature dependences of vapor pressures. The measured data sets were successfully checked for internal consistency by comparison with vaporization enthalpies of the parent species, and a group contribution method is put forth by which the vaporization enthalpies of imidazoles, and imidazolium-based ILs, with alkyl groups in any configuration can be rapidly predicted.

Experimental and Computational Study of the Properties of Imidazole Compounds with Branched and Cycloalkyl Substituents

“…Compounds 1-6 used for characterizations were determined to contain <5 × 10 −4 mass fraction of impurities by Hewlett-Packard 5890 Series II gas chromatography with a flame ionization detector. 1 H NMR data obtained from a Bruker AVANCE 500 MHz NMR spectrometer in the Chemistry Department at the University of Alabama showed good consistency with previously published spectra and can be found in our previous publication [30] as they were from the same…”

“…Compounds 1-6 used for characterizations were determined to contain <5 × 10 −4 mass fraction of impurities by Hewlett-Packard 5890 Series II gas chromatography with a flame ionization detector. 1 H NMR data obtained from a Bruker AVANCE 500 MHz NMR spectrometer in the Chemistry Department at the University of Alabama showed good consistency with previously published spectra and can be found in our previous publication [30] the five-membered ring [14], allowing for great versatility in the design of N-functionalized imidazoles and corresponding imidazolium ILs. Moreover, N-functionalized imidazoles have a plethora of other uses such as metal extraction [15,16], gas separation [17], temperature swing solvent extraction (TSSE) [18] and can provide correlations for prediction on densities of corresponding ILs [19].…”

“…All the N-functionalized imidazole compounds studied in this work were synthesized as shown in Scheme 1, in which imidazole was deprotonated by NaOH, creating sodium imidazolate as an intermediate towards the formation of modified imidazoles via reaction with corresponding halide compounds. Detailed synthetic procedures for these compounds can be found in our prior works [29,30]. Compounds 1-6 used for characterizations were determined to contain <5 × 10 −4 mass fraction of impurities by Hewlett-Packard 5890 Series II gas chromatography with a flame ionization detector.…”

“…Vapor pressures of branched and cycloalkyl imidazoles considered have been measured previously and enthalpies of vaporization were calculated accordingly [30]. COS-MOtherm calculations were applied in the current study with the complete results shown in Table S4 with compilation of measured values for comparison purpose.…”

Fine tuning the electronic structure of Ni(II), Fe(II) and Ru(II) complexes with 2-aryl-imidazoles

“…A term "designer solvent" has been coined up in recent years for such heterocyclic rings, which can be modified into structures of desired properties by introducing different substituents on the ring. Imidazole can be contoured by manipulating at four different positions in the ring (Verevkin et al, 2015) Protonation results in a decrease of electronic density over these rings, while deprotonation leads to the opposite effect (Figure 2.1). This possibility of tailoring the electronic density by protonation or deprotonation can be useful for the planning and development of coordination polymers and polynuclear complexes with applications in materials chemistry (Singh & Bharadwaj, 2013;Coronado et al, 2012), bioinorganic (Serratrice et al, 2012) and catalysis (Stott et al, 2017).…”