| Amines and their derivatives are prevalent functionalities in various natural products and unnatural synthetic targets. Due to their numerous applications in polymers, dyes, agrochemicals, and pharmaceuticals, there is an ongoing interest for new synthetic preparations. Nowadays, more and more chemical researchers start to use alcohols as intoxic, inexpensive and readily available alkylation reagents. It will become a new research direction of the N-alkylation reaction.The focus of this paper lies in realizing the selective control of two main types of N-alkylated products, i.e. N-benzylideneanilin and N-phenylbenzylamine, by controlling the reaction conditions.Co2+-exchanged zeolite catalysts were prepared by an ion-exchange route and firstly applied in the N-alkylation of aromatic amines with alcohols to imines. The aniline conversion of89.8mol%with an imine selectivity of100%was achieved over Co-13X at433K under optimal conditions. The results showed that many factors including the Co loading, the support, the temperature, the alkali, could influence the reactions. Investigations carried out by XRD, SEM, BET, XRF and recycling studies indicated that the Co-13X catalyst still remained porous structures of13X zeolite and possessed a stable catalytic activity.In the process of selective synthesis of the secondary amine, different from any other catalytic systems containing transition metals and aldehyde additives, sodium hydroxide itself was found to be a unique and effective catalyst for this reaction. Some factors inclusive of the kind of base, the amount of base, reaction temperature, reaction time, molar ratio of substrate etc. were investigated in detail respectively. Under optimal conditions, the aniline conversion of99.6mol%with a secondary amine selectivity of99.5%was achieved at493K. In addition, various amines could react with alcohols to gain high conversions and selectivities, implying the universality of this methodology. Mechanistic studies revealed that this novel reaction most possibly proceeds with a simple but distinctive base-catalyzed mechanism. |
