The sustainable and catalytic synthesis of N,N-alkylated fatty amines from fatty acids and esters†

Abstract

The reductive amination of fatty acids (FAs) and fatty acid methyl esters (FAMEs) has been identified as a green and effective method to produce N,N-dimethylalkylamines (ADMAs). With current technology, this reaction requires at least two reaction steps. Here, we report a heterogeneous catalytic system for the one-pot synthesis of ADMAs from FA(ME)s, utilizing solely H₂ and methylamines (i.e. di- and trimethylamine). The reaction requires two recyclable catalysts: ortho-Nb₂O₅ for the amidation of FA(ME)s and PtVO_x/SiO₂ for the hydrogenation of the in situ generated fatty amide to ADMAs. The developed system has a wide range of applicability: it is able to convert all natural FAs to ADMAs (yields up to 90%) and also other tertiary amines were synthesized. Aside from the development of a sustainable and industrially applicable process (e.g. utilizing benign solvents or performing solventless reactions), a kinetic model was developed that describes the reaction rate's relationship with key process parameters such as the H₂ pressure and water content. By tuning the reaction conditions, different ratios of primary, secondary and tertiary fatty amines can be obtained.