Using ionic liquid as solvent for coupling, and halogen exchange reactions
In this research, 1-alkyl-3-methyl imidazolium bromide ionic liquids were successfully synthesized under microwave conditions. After that, 1-alkyl-3-methyl imidazolium hexafluorophosphate [AMIM]PF6 ionic liquid was prepared by anion exchange reaction of dialkylimidazolium bromide with hexafluorophosphoric acids. The structural properties of prepared ionic liquids were characterized by using Nuclear Magnetic Resonance (1H, 13C NMR) and Mass Spectrometry (MS) analysis. More interestingly, the results showed that dialkylimidazolium ionic liquid could effectively act as green solvents for coupling reactions, and halogen exchange reaction with high conversion under low temperature and shorter reaction time in comparison with conventional solvents. Some typical results are described below: Reaction 1. The condensation reaction of salicylaldehyde and methyl acetoacetate formed 3-acetylcoumarin with approximately 86% conversion after 3 hours at 100 °C with, [BMIM]Br ionic liquid as a solvent. Reaction 2. The condensation reaction between 1,2-phenylenediamine and acetone to synthesize 1,5-benzodiazepine could occur at 45 oC with 100% conversion after 3 hours in [HMIM]Br ionic liquid. Reaction 3. The N-aryl reaction between piperidine and 4-bromonitrobenzene to form 1-(4-nitrophenyl) piperidine can reach approximately 94% conversion after 3 hours with [BMIM]Br as a solvent at 90 oC. Reaction 4. 1-(2-(N-morpholino)ethyl)-2-methylindole was synthesized by the reaction between 1-(N-morpholino)-2-chloroethane hydrochloride and 2-methylindole formed with about 75% conversion after 7 hours in [BMIM]PF6 ionic liquid at 30 oC. Reaction 5. Paal-Knorr reaction for synthesis of pyrroles was performed [BMIM]PF6 ionic liquid with 100% conversion after 40 minutes at 30 oC. Reaction 6. Halogen exchange reaction between aryl iodides and copper (I) bromide to form aryl bromide derivatives could reach more than 90% conversion in [BMIM]Br ionic liquid as a solvent after 8 hours at 140 oC. Page v Interestingly, the recycle of [BMIM]Br ionic liquid was performed. The results showed that [BMIM]Br ionic liquid can be recovered and successfully recycled into subsequent reactions without significant loss of activity. The main products were identified by GC-MS and NMR.