Effective synthesis of 5-amino-1-pentanol by reductive amination of biomass-derived 2-hydroxytetrahydropyran over supported Ni catalysts

Abstract

A highly efficient and green process was developed for the synthesis of useful 5-amino-1-pentanol (5-AP) from biomass-derived dihydropyran by coupling the in situ generation of 5-hydroxypentanal (5-HP, via the ring-opening tautomerization of 2-hydroxytetrahydropyran (2-HTHP)) and its reductive amination over supported Ni catalysts. The catalytic performances of the supported Ni catalysts on different oxides including SiO2, TiO2, ZrO2, γ-Al2O3, and MgO as well as several commercial hydrogenation catalysts were investigated. The Ni/ZrO2 catalyst presented the highest 5-AP yield. The characterization results of the oxide-supported Ni catalysts showed that the Ni/ZrO2 catalyst possessed high reducibility and a high surface acid density, which lead to the enhanced activity and selectivity of the catalyst. The effect of reaction parameters on the catalytic performance of the Ni/ZrO2 catalyst was studied, and a high 5-AP yield of 90.8% was achieved in the reductive amination of 2-HTHP aqueous solution under mild conditions of 80 °C and 2 MPa H2. The stability of the Ni/ZrO2 catalyst was studied using a continuous flow reactor, and only a slight decrease in the 5-AP yield was observed after a 90-h time-on-stream. Additionally, the reaction pathways for the reductive amination of 2-HTHP to synthesize 5-AP were proposed.