Mechanistic Insight into Selective Deoxygenation of <scp>l</scp>-Lysine to Produce Biobased Amines

Abstract

The shift in consumer preference toward eco-friendly plastic products is driving the overall bioplastics and biopolymers market. As such, there is a strong demand for innovative processes that produce monomers from biomass feedstocks as an alternative to fossil resources. For instance, amino acids with two amino groups (e.g., l-lysine) are a unique biomass material that can be refined to produce diamines, which are further used to synthesize biobased nylons. Herein, we demonstrate that the diamine (cadaverine) was produced in a high yield from the second most-produced commercial amino acid (l-lysine). In the selective deoxygenation of lysine, the synergistic effect of the carbon-supported ruthenium catalyst and the phosphoric acid cocatalysts, the role of hydrogen gas, and the activation and suppression of the functional groups of lysine were elucidated in great detail. Under the optimum conditions, a 100% conversion of l-lysine and an ∼94% total yield of amines, with an ∼51% selectivity to diamines, were attained at 200 °C within 2 h. Moreover, both characterization and kinetic studies of the probe reactions were used to understand the reaction mechanism. The knowledge gained in this study may provide fundamental insights into the selective deoxygenation of other N-containing renewable feedstocks.