Abstract: A series of N-carboxyl appended pyridinium task-specific ionic liquids(TSILs) were synthesized and characterized by 1H NMR, 13C NMR, IR, and DSC. The miscibilities of these TSILs with conventional solvents were studied and the acid-dissociation constant pKa values of them were measured through titration. The pKa values of N-carboxyl appended TSILs were between 2.5 to 4.0 and increased with increasing alkyl chain length. The melting points of N-carboxyl appended TSILs were influenced extensively by the size of ions and hydrogen bonds formed between the ions, the smaller the anion size is, the higher the melt point is. With conventional organic solvents, the miscibilities of all synthesized N-carboxyl appended TSILs were the same and mainly determined by the substituted carboxyl. Contrary to common imidazolium ILs, N-carboxyl appended TSILs were immiscibe with acetone and dichloromethane. The physical properties of TSILs were mainly affected by the substituted group and could be adjusted with task-specified cation, changing the length of substituted group, or combining of the selected cation and anion.

Key words: Task-specific ionic liquids, Carboxyl, Pyridine, Characterization, Acidic properties, Miscibility