Selective Conversion of Cellulose into Azaheterocycles through Pyrolysis under a Reactive NH 3 Atmosphere

Azaheterocycles are essential building blocks for high-value chemicals traditionally derived from fossil fuel intermediates. This study provides a fundamental investigation into the production of these compounds from cellulose as a renewable resource, by means of nitrogen-rich pyrolysis at the microscale. Herein, a strategy is demonstrated for the first time to perform micropyrolysis under an NH 3 -rich atmosphere while controlling the reaction time between the cellulose’s pyrolysis intermediates and NH 3 . This is achieved by using urea and ammonium carbamate as NH 3 precursors within a specific online microreaction sampler for micropyrolysis. Micropyrolysis experiments were conducted at 500 °C to elucidate the importance of the N-source and to determine the influence of nitrogen-to-biomass ratios and reaction time on product distribution. Under optimized conditions (30 s reaction time, nitrogen source-to-biomass ratio of 10:1), a remarkable yield in azaheterocycles of 48 C-wt % was achieved with a total azaheterocycle selectivity of 87%. The main contributor was pyrrole with a selectivity of 31%. Mechanistic pathways were elucidated by reacting key cellulose-derived intermediates (cellobiose, levoglucosan, acetol, and glycolaldehyde) with ammonium carbamate. The results demonstrate two pathways: pyrroles are predominantly formed via furanic intermediates, while pyrazines, oxazoles, and pyridines originate from light oxygenates (e.g., acetaldehyde, acrolein, and glycolaldehyde). These findings suggest that the NH 3 release mechanism and reaction time are critical in governing nitrogen-incorporation pathways and establishing pyrolysis under a reactive NH 3 atmosphere as a promising method for the selective synthesis of biobased azaheterocycles.