Selective Oxidative Coupling Of Benzylamine To Imines Catalyzed By Organically Modified Manganese Dioxide

It is one of the most effective strategies to improve the reaction selectivity via the interaction between organic molecules and the surface of catalyst.Proton molecules,such as organic acids and acetylacetone,interact with the catalyst surface.The dissociatively adsorbed anions can effectively block Lewis acidic sites on the surface of metal oxide catalysts.But the effect of dissociatively adsorbed cations on catalytic oxidation activity and selectivity remains unclear.This work was devoted to address this key scientific question.Benzylamine oxidation was selected as a model reaction.The effect of the type and structure of modified molecules on the activity and selectivity of manganese oxide catalysts was studied using aprotic molecule modification strategy.The main results are as follows:In this thesis,benzylamine oxidation catalyzed by aprotic ionic liquid modified with MnO2 was studied.It was found that when the ionic liquid 1-butyl-3methylimidazolium acetate([BMIm][Ac])was used as the modified molecule,the oxidative coupling selectivity was greatly improved,and it had little effect on the catalytic activity.Under the optimized reaction conditions,the benzylamine conversion was 94%and the imine selectivity was 95%.The results of in situ pyridine adsorption infrared demonstrate that ionic liquid 1-butyl-3-methylimidazole acetate can interact with the catalyst MnO2 surface to selectively block Lewis acid sites on the MnO2 surface,which in turn inhibits hydrolysis-ammoxidation of imines to nitriles.The effect of benzylamine oxidation catalyzed by tertiary aprotic amine modified with MnO2 was studied.The imine selectivity has greatly impoved over aprotic molecule of N,N-dimethylcyclohexylamine(DMCHA)modified MnO2 catalyst,with its redox activity mostly unaffected.And this modified MnO2 has a better substrate applicability.Moreover,the DMCHA modified catalyst can be recycled for 3 times,suggesting that the regulating effect of DMCHA on MnO2 is not destroyed after processing under the reaction conditions.The selectivity regulation mechanism was further investigated for the DMCHA modified catalyst via infrared,in situ pyridine adsorption infrared and control tests.These results manifest that the associative adsorption of DMCHA resulting from the acid-base interaction is effective to block the Lewis acidic sites on the surface of manganese oxides,resulting in amine highly selective oxidative coupling to imine.