Abstract
A series of dicationic ionic liquids (ILs) including [C4(MIM)2][PF6]2, [C5(MIM)2][PF6]2, [C6(MIM)2][PF6]2 and [C4(PYR)2][PF6]2 were synthesized. Their thermal stability and melting points were analysed. It was found that dicationic ILs presented important implications in the design of homogeneous and heterogeneous system with water. A homogeneous system of dicationic ILs with water could be formed at a relatively high temperature and then a heterogeneous system was formed when the solution was cooled to a low temperature. The ILs recovered by altering the temperature were obtained in high percentage yields of [C4(MIM)2][PF6]2 (97.6%), [C5(MIM)2][PF6]2 (97.3%), [C6(MIM)2][PF6]2 (98.0%) and [C4(PYR)2][PF6]2 (94.2%). On the other hand, [C4(MIM)2][PF6]2 and [C5(MIM)2][PF6]2 exhibited good solubility in acetonitrile and acetone. A homogeneous system could be achieved with imidazolium-based ILs with a relatively low amount of water and acetonitrile at room temperature. All of the properties of dicationic ILs have a strong correlation with the nature of dications, the linkage chain and the symmetry of dications. Dicationic ILs may provide a new opportunity for some specific applications in order to enable the effective separation and isolation of products.
Highlights
Ionic liquids (ILs) have received wide popularity in recent years in the areas of electrochemistry [1], catalytic reactions [2], organic synthesis [3], separation technology [4] and biochemistry [5]
The thermal stability of dicationic ILs was determined by thermogravimetric analysis (TGA). 5– 10 mg of the sample was placed in an open alumina plate by using a TG 209 F3 thermogravimetric analyser (NETZSCH, Germany)
Dicationic ILs were synthesized through commonly used quaternization reaction followed by anion metathesis
Summary
Ionic liquids (ILs) have received wide popularity in recent years in the areas of electrochemistry [1], catalytic reactions [2], organic synthesis [3], separation technology [4] and biochemistry [5]. ILs with the anion of PFÀ6 and NTfÀ2 are water-immiscible, whereas others are completely water-miscible. Dicationic ILs generate good thermal stability [19], high conductivity and low electrochemical window [20] They have been shown to possess superior physico-chemical properties as solvents of high temperature organic synthesis or as a gas chromatography stationary phase, because these applications were often conducted at relatively high temperatures [21–24]. The main goal of this investigation was to increase knowledge in physicochemical properties of dicationic ILs. The main attention was focused on the investigations of (a) its thermal stability, (b) its melting points and (c) its solubility in water and water-organic mixtures. The properties of dicationic ILs including thermal stability, miscibility with water and water-organic mixtures could be important for their use as solvents or catalysts in various applications
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