Switchable Hydrophilicity Amine Product Extraction: Efficient Separation of Tertiary Amines via Carbon Dioxide-Induced Polarity Switch in Homogeneous Catalysis

Abstract

A combined approach is presented for the homogeneously catalyzed synthesis of tertiary amines and their subsequent carbon dioxide (CO₂)-induced separation. After production, the nonpolar tertiary amines are reacted with carbon dioxide to the corresponding polar ammonium carbonates and separated from the nonpolar reaction phase by water extraction. Subsequently, the nonpolar tertiary amines reform upon CO₂-stripping the loaded aqueous phase, enabling their straightforward isolation by decantation. For this Switchable Hydrophilicity Amine Product Extraction (SHAPE) concept, the influence of various nonpolar solvents on the separation efficiency was investigated using N,N-dimethylbenzylamine (DMBA) as the model amine. After examination of all operating parameters of SHAPE in anisole as the best-performing solvent, homogeneously Ru-catalyzed alcohol amination of benzyl alcohol was identified as the most suitable model reaction for the production of DMBA, which was successfully isolated in 84.9% yield using SHAPE methodology. Moreover, only 0.09 wt % of Ru was lost in the separated product phase. This SHAPE concept was successfully combined with catalysis in thermomorphic multiphase systems (TMS). Four different tertiary amines were efficiently separated from the nonpolar solvent and the other reaction components, achieving high product purities of up to 97.3 wt %.