Ultrasound assisted the preparation of 1-(4-nitrophenyl) imidazole under a new multi-site phase-transfer catalyst – Kinetic study

• A new multi-site phase-transfer catalyst was used for the preparation of 1-(4-nitrophenyl) imidazole.
• Different frequency of ultrasound irradiation was tested.
• A suitable reaction mechanism was proposed for this reaction.

In this work, the nitroarylation of imidazole catalyzed by a new novel dual-site phase-transfer catalyst was carried out in an alkaline solution/imidazole in chlorobenzene two-phase medium with ultrasonic irradiation (40 kHz, 300 W). This new synthesized phase-transfer catalyst, N1,N6-diethyl-N1,N1,N6,N6-tetraisopropylhexane-1,6-diaminium dichloride (MPTC), which possesses two-site activity, was obtained from the reaction of 1,6-dichlorohexane and N-ethyl-N-isopropylpropane-2-amine. The reaction of imidazole and alkali was carried out at the interface to generate sodium imidazole anion which can further react with MPTC form quaternary ammonium imidazole anion along with ultrasonic irradiation (40 kHz, 300 W). This ion-pair further react with 1-chloro-4-nitrobenzene which is present in the organic phase to produce 1-(4-nitropheny) imidazole. The reaction follows a pseudo first-order rate law. Kinetics of the reactions such as effect of the catalysts, ultrasonic effect, agitation speed, temperature, alkaline concentration, amount of 4-nitrochlorobenzene and the solvent effect on the reaction rate were investigated in detail. Peculiar phenomenon for the dependence of the reaction rate on the amount of MPTC and ultrasonication are explained satisfactorily.