Dialkylimidazolium structure

Headley and coworkers developed suJfamides St9a [109], 99b [110], and 100 (Figure 22.8) [111] bearing the (S)-pyrrolidine and 1,3-dialkylimidazolium structural units, which exhibited a high catalytic performance in asymmetric Michael additions of enolizable aldehydes or ketones to P-nitrostyrene derivatives. Sulfa-mide 100 [111] and ClL-catalyst 101 synthesized by Xu and coworkers [112], in... 

Domarfska, U., Marciniak, A., and Bogel-Lukasik, R., Phase equilibria (SLE, LLE) of N, N-dialkylimidazolium hexafluorophosphate or chloride, in Ionic Liquids lllA Fundamentals, Progress, Challenges, and Opportunities Properties and Structure, R.D. Rogers and K.R. Seddon (Eds), Washington, D.C., 2005 ACS, NY, 2003. 

Biocatalysis in ionic liquids was first reported in 2000 [7, 8, 9]. The early work involved ionic liquids composed of a 1,3-dialkylimidazolium or N-alkylpyridinium cation and a weakly-coordinating anion (Figure 10.1). More recently, attention is shifting toward new structural types. A number of reviews of this rapidly expanding subject have appeared [10, 11, 12, 13, 14]. 

Finally, X-ray diffraction has been used to examine the liquid structure of binary ionic liquids of 1,3-dialkylimidazolium fluoride with HF [173,174], The solid state and liquid structures are closely related as both contain [HF2] anions. In contrast, Shodai et al. reported that the structure of liquid [(CH3)4N]F HF (n = 3-5) has a range of anion structures of the form [(HF)jcFp (x = 1-3). In this case, structures with x = 4 or 5 were not found in the liquid phase although similar compositions have been found in the solid state [175], These studies show that even elements that are rarely studied in the IL context like P (other than in PF ( or phosphonium cations) or F could provide access to interesting and potentially useful ILs. 

In this chapter, we presented an approach related to the molecular-microscopic properties of binary mixtures composed of two types of ILs - alkylammonium and dialkylimidazolium-based ILs - with molecular solvents of different structures. 

Ionic liquids differ from classical molten salts by being liquids at room temperature, or their melting points are below 100 °C. They have an ionic structure and usually consist of an organic cation and an inorganic or organic anion. The most common cations found in ionic liquids are the tetraalkylammonium, tetraalkyl-phosphonium, N-alkylpyridinium, 1,3-dialkylimidazolium, and trialkylsulfonium moieties [11]. Some common ionic liquid cations and anions are presented in Fig. 7.1. 

Not surprisingly, these materials are very popular and enjoy a plethora of applications in various domains of the physical sciences, and an impressive number of spedahzed reviews and books has appeared dealing with their synthesis, physicochemical properties and appHcations in synthesis, catalysis and separation processes [12-26]. This section does not intend to be comprehensive on the vast area of synthesis and appHcations of ILs rather it will attempt to provide a critical update of the basic principles and latest developments on the structure and properties of ILs (mainly those based on the 1,3-dialkylimidazolium cation), and their... 

This structural pattern is even maintained in the gas phase and evidence for the clustering - supramolecules formed through association of the 1,3-dialkylimidazolium cations with the anions - has been obtained by mass spectrometry expert-... 

In contrast to the increasing information on the bulk properties of ionic liquids, very little is known about the interfacial structure of ionic liquids with other phases. Examinations of gas-ionic liquids inter ces of 1,3-dialkylimidazolium-based liquids using direct recoil spectroscopy [41] or sur ce vibrational spectroscopy [42-44] have provided some general indicative information about the sur ce composition... 

In COlL-1, all of the main aspects of the liquid-state structure of room-temperature ionic liquids were already laid out in contributions by several groups, although sometimes still in an incipient way. Hardacre and co-workers reported neutron diffraction studies of short-chain dialkylimidazolium ionic liquids, perfectly illustrating the charge ordering and n-interactions [17]. They also used different spectroscopic and simulation methods to study how the solvation of aromatic and polar molecules (benzene and ethanenitrile, respectively) in the ionic liquids modifies the structure of the media [46] and the balance between the different terms in the interactions coulombic, van der Waals (dispersive), hydrogen bonds and multipolar. 

Several 1,3-dialkylimidazolium halides have been intensely structurally investigated, not only as a consequence of polymorphism but also as subjects of studies of the dynamics of processes occurring during melting and crystallisation and associated butyl group conformer lability. These aspects have been introduced in Section 11.2. 

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