Chemoenzymatic synthesis of amino-esters as precursors of ammonium salt-based surfactants from 5-hydroxymethylfurfural (HMF)

Abstract

N-Substituted 5-(hydroxymethyl)-2-furfuryl amines have been obtained through the reductive amination of 5-hydroxymethylfurfural (HMF) with a variety of primary amines using a non-noble metal catalyst based on monodisperse Co nanoparticles covered by a thin carbon layer. The Co@C catalyst was highly active, selective and stable, allowing us to perform the reductive amination of HMF under very mild reaction conditions (60 °C and 4 bar H₂) using ethanol as a green solvent and achieve the corresponding amino-alcohol in yields ranging from 80 to 99%. Moreover, the reaction was extended to other furanic aldehydes with excellent success. Furthermore, in order to synthesize amino-ester derivatives, precursors of ammonium salt-based surfactants, the reductive amination of HMF with methylamine was coupled with the selective esterification of the hydroxymethyl group of the furan ring with fatty acids using lipase CALB (Novozym 435) as a biocatalyst in 2-methyltetrahydrofuran as a green and enzyme compatible solvent, achieving practically total conversion to the corresponding amino-esters. The process was implemented in flow reactors by combining two consecutive fixed bed reactors, achieving a global yield of the amino-ester derivative of 85%, which was maintained over 86 h of operation.