(27b) Synthesis of Fatty Amines: Rhodium-Catalyzed One-Pot Hydroaminomethylation of 1-Decene in an Aqueous Multiphase System

Fatty amines are of great interest due to their diverse technical applications as corrosion inhibitors or precursors for surfactants. The synthesis from olefins, also known as hydroaminomethylation, is a multi-step route consisting of hydroformylation and a reductive amination with a homogeneous catalyst for both reactions. Due to the increasing demand for green chemistry, the combination of two reactions in a one-pot synthesis reduces operation costs for the process and from a sustainable point of view the use of an aqueous multiphase system enables the recycling and reuse of the homogeneous catalyst complex.

Since the same catalyst complex is used for both reactions, the reaction conditions must be well chosen in order to ensure the optimum for the entire hydroaminomethylation process. Based on kinetic and mechanistic studies the optimal reaction conditions for the multi-step reaction were determined. Increasing pressure of synthesis gas leads to a decreasing initial reaction rate for the hydroformylation reaction whereas an increase in the initial reaction rate can be observed for the reductive amination (see figure 1). Due to different catalyst cycles for the sub-steps and the resulting different active catalyst species for each reaction the synthesis gas has a strong impact on the catalyst equilibria. Over the entire pressure range, the regioselectivity for the hydroformylation remained constant (98% linear aldehyde) and no branched fatty amine was observed. Side reactions like aldol condensation, alcohol reduction, or the olefin-isomerization were slightly observed.

Furthermore, the water content has turned out to be a challenging parameter for a successful conversion due to the role of water as a product in the condensation reaction between the aldehyde and the diethylamine. This makes the implementation of an aqueous multiphase system challenging; however, our results are promising, and catalyst recycling and reuse are planned for the near future.