Direct imine formation by oxidative coupling of alcohols and amines using supported manganese oxides under an air atmosphere

Abstract

Manganese oxides loaded on various supports have been prepared and studied for the direct imine formation by oxidative coupling of alcohols and amines. Among the catalysts, hydroxyapatite supported manganese oxides (MnO_x/HAP) show the best activity and selectivity for this reaction in the absence of an additional base using air as the environmentally benign terminal oxidant. NH₃-/CO₂-TPD results show that the amphoteric properties of MnO_x/HAP are crucial for this reaction to obtain a satisfactory yield. Various aromatic alcohols and amines are smoothly transformed into the corresponding imines in good to excellent yields. The catalyst is reusable and gives 98% yield of the product in all 9 reuse tests. Compared with the fresh catalyst, the XRD and SEM of the reactivated MnO_x/HAP after nine reactions do not show any obvious change.