| Ionic liquids have been shown to be very promising "green" solvents with several advantages compared to traditional oraganic solvents. Most notably, their nonvolatility, high thermal stability, and extraordinary solvent properties make them important solvents for the chemical industry. Ionic liquids (ILs) are salts which contain only organic cations and organic or inorganic anions, which lead to a large number of possible combinations. Therefore, many of their physicochemical properties have previously been tuned by changing the kinds of anions. The main content we studied in this paper is the change rule of properties in ionic liquids by modifying the aryl substitution on the guanidinium salts. The main content is outlined as following:We used tetraalkylureas and oxalyl choride as the starting materials to synthesize a series of aryl guanidines, which subsequently reacted with halogenoalkanes, twenty guanidinium halide ILs were obtained. We also synthesized six halogen-free guanidinium salts ILs by metathesis method. All the structures of gunidines and guanidinium salts ILs were determined by NMR. Then we studied the physico-chemical properties of some of the ILs, involving sobubility, melt point and thermal stability. The results are as following:The aryl substituent on the cation can effectively influence the melting points of the guanidium salts. Along with the increase of the carbon numbers(C2-C5) of the alkyl substituted groups on the nitrogen atom of the guanidium salt ILs, the melting points of the guanidium with [PF6] anions decrease. The aryl substituents also have a large impact on the solubility in organic solvent. The decomposition temperature can greatly enhane when changing the anions of aryl guanidinium salts ILs from halogen into [PF6].A series of guanidines and guanidinium salts ILs with different aryl substituents were synthesize and characterized in this paper, further studies and applications of this kind of ILs are ongoing in our labbratory.
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