Efficient and Solvent-Free Oxidation Coupling of Amines to Imines Using Persulfate as Oxidant with Ultrasound Assistance

The coupling reactions of amines into imines oxidized by persulfate with the assistance of ultrasound were carried out. The reaction conditions were optimized and the effect of ultrasonic was also investigated. The results indicated that Na2S2O8 in combination with ultrasound possessed excellent oxidative performance, which made this transformation smoothly proceed under the conditions of solvent-/catalyst- free, and low reaction temperature, giving excellent yields of imines in short reaction time. Our procedure had high reaction tolerance to various primary benzylic amines, demonstrating good universality. Furthermore, a tentative reaction mechanism and pathway were proposed.