Tandem Catalytic Amine Synthesis from Alkenes in Continuous Flow Enabled by Integrated Catalyst Recycling

We present the development of catalytic autotandem reactions into continuous-flow processes on the example of homogeneously catalyzed hydroaminomethylation (consisting of hydroformylation and subsequent reductive amination) as a case study. The synthesis of higher aliphatic amines was successfully operated in a continuous-flow miniplant. Key to success was the development of an integrated catalyst recycling for the homogeneous Rhodium/SulfoXantphos catalyst. With 1-decene and diethylamine as substrates, an average yield of the linear amine of 61% over 60 h of stable process operation was achieved. The catalyst recycling has been accomplished by using a thermomorphic multiphase system (TMS) consisting of methanol and n-dodecane, which was rationally established in batch experiments with a methodical approach. This TMS ensured high catalytic activities and facilitated an efficient catalyst separation and recycling. Before application in a continuous process, catalyst recyclability was proven, showing high catalyst activity over six runs with turnover frequencies up to 2400 h(-1).