Expanding the Boundary of Biorefinery: Organonitrogen Chemicals from Biomass

Organonitrogen chemicals are essential in many aspects of modern life. Over 80% of the top 200 prescribed pharmaceutical products contain at least one nitrogen atom in the molecule, while all top 10 agrochemicals contain nitrogen, just to name a few. At present, the prevailing industrial processes for manufacturing organonitrogen chemicals start from nonrenewable fossil resources, but eventually we have to make these chemicals in a more sustainable manner. Biomass represents the largest renewable carbon resource on earth, which is inexpensive and widely available. Integrating biomass into the organonitrogen chemical supply chain will mitigate the carbon footprint, diversify the product stream, and enhance the economic competitiveness of biorefinery. Short-cut synthesis routes can be created for oxygen-containing organonitrogen compounds by exploiting the inherent oxygen functionalities in the biomass resources. Moreover, for nitrogen-containing biomass components such as chitin, a unique opportunity to make organonitrogen chemicals bypassing the energy-intensive Haber-Bosch ammonia synthesis process arises. Estimated at 100 billion tons of annual production in the world, chitin captures more nitrogen than the Haber-Bosch process in the form of amide functional groups in its polymer side chain. In this Account, we intend to summarize our efforts to establish new reaction routes to synthesize valuable organonitrogen chemicals from renewable resources. Enabled by tailor-designed catalytic systems, diverse nitrogen-containing products including amines, amino acids, nitriles, and N-heterocycles have been obtained from a range of biomass feedstock either directly or via intermediate platform compounds. Two strategies to produce organonitrogen chemicals are presented. For platform chemicals derived from cellulose, hemicellulose, lignin, and lipids, which are enriched with oxygen functionalities, in particular, hydroxyl groups, the key chemistry to be developed is the catalytic transformation of hydroxyl groups into nitrogen-containing groups using NH3 as the nitrogen source. Along this line, Ru- and Ni-based heterogeneous catalysts are developed to convert alcohols to amines and/or nitriles via a thermal catalytic pathway, while CdS nanomaterials are explored to promote -OH to -NH2 conversion under visiblelight irradiation. Metal-zeolite multifunctional systems are further established to enable the synthesis of N-heterocycles from O-heterocycles. The second strategy involves the use of chitin and chitin derivatives as the starting materials. Under the concept of shell biorefinery, distinctive protocols have been established to chemically transform chitin as the sole feedstock to amino sugars, amino alcohols, furanic amides, and N-heterocycles. By combining mechanochemistry with biotransformation, an integrated process to convert shrimp shell waste to complex, high-value, chiral compounds including tyrosine and (L)-DOPA is also demonstrated.