Synthesis and investigation of physico-chemical properties of dicationic ionic liquids

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.

Linking the Thermal and Electronic Properties of Functional Dicationic Salts with Their Molecular Structures

“…Longer chains are better at disrupting the Coulombic interactions of cations and anions, which helps to suppress their melting points; however, as chains lengths continue to increase, Van der Waals forces between aliphatic chains act to increase the melting points . Similar trends have also been observed for geminal imidazolium dicationic salts, but the identity of both the cation and anion can have drastic effects on this trend. , …”

“…44 Similar trends have also been observed for geminal imidazolium dicationic salts, 19 but the identity of both the cation and anion can have drastic effects on this trend. 45,46 [(C n Im) 2 Py][NTf 2 ] 2 salts readily formed supercooled liquids that underwent glass transitions (T g ), and in some cases (n = 2, 6, and 8), cold crystallization (T cc ) occurred, followed by solid−solid transitions (T ss ) of the crystallized A decrease in T m usually occurs when switching Br − to [PF 6 ] − in monocationic imidazolium salts, 50 but an increase in T m has been reported for one other monocationic benzimidazolium salt 51 (there are limited reports for benzimidazolium thermal properties). The [PF 6 ] − anion has an extremely low hydrogen bond acceptor (HBA) ability compared to most other anions, 52 which indicated that H-bonding was as important as anion size and flexibility for lowering melting points of pyridine-bridged salts.…”

Scrutinizing Self-Assembly, Surface Activity and Aggregation Behavior of Mixtures of Imidazolium Based Ionic Liquids and Surfactants: A Comprehensive Review

“…In the case of CSAILs, the long hydrophobic chain is present in the cationic part of SAIL, giving rise to similar properties like conventional cationic surfactants (Zhao and Zheng, 2011 ; Gu et al, 2013 ; Cognigni et al, 2016 ; Zhao et al, 2017 ). CSAILs can be subdivided into two types namely dicationic surface-active ILs (DCSAILs) and Gemini cationic surface-active ILs (GCSAILs) (Baltazar et al, 2007 ; Ao et al, 2008 ; Khan et al, 2017 ; Ziembowicz et al, 2017 ; Zhou et al, 2018 ). Similarly, if the long hydrophobic chain is present in the anionic part of SAIL exhibiting the properties similar to anionic surfactants, then they will be considered as ASAILs (Jiao et al, 2012 , 2013b ; Srinivasa Rao et al, 2014 ).…”

Synthesis of functional dicationic ionic liquids for the treatment of lignocellulosic biomass

“… 12 The pyridinium cation was introduced into the dications of DILs because pyridinium-based ILs were observed to generate poor solubility with water. 19 In this study, these DILs exhibiting hydrophobic or acidic properties could be potentially utilized in various applications.…”