Efficient synthesis of imine from alcohols and amines over different crystal structure MnOx catalysts

The redox properties of different crystal structure MnO2 in organic reactions at low temperature of 60 degrees C were disclosed. Among the three crystal structures (alpha-, beta- and y-types), gamma-MnO2 showed unusual high heterogeneous catalytic performance, reusability and stability for imine formation from benzyl alcohol and aniline under mild conditions. The yield of imine over gamma-MnO2 reached up to 98.1% in 12 h under air atmosphere and its formation rate per surface area was 27.9 mu mol h(-1) m(-2), and various imines could be obtained in excellent yield over gamma-MnO2. Based on series of catalyst characterizations, it was found that the high activity of gamma-MnO2 was mainly attributed to its high concentration of low-valence manganese ions. Furthermore, the catalytic mechanism was also disclosed. This research may have certain reference value for heterogeneous catalytic reactions by manganese.