Polyaniline-functionalized biochar (PANI@ALB) as a heterogeneous acid–base bifunctional catalyst for one-pot cascade reactions under green reaction conditions

A sustainable, eco-friendly, and economical approach is developed to design a well-architectured polyaniline-functionalized biochar (PANI@ALB) as an acid–base bifunctional heterocatalyst for one-pot cascade reactions involving the synthesis of complex 2-amino-4H-pyran-3-carbonitrile derivatives. The activated biochar (ALB), derived from the pyrolysis of lac tree (Schleichera oleosa) leaves, is intercalated with PANI nanosheets via an in situ acid-catalyzed oxidative polymerization process to obtain PANI@ALB, the desired acid–base catalytic system. PANI@ALB exhibits enhanced catalytic activity compared to biochar or polyaniline (PANI). The superior performance of PANI@ALB has been ascribed to the synergistic effect between H⁺ and –NH– & N– of biochar and PANI, respectively, confirmed by the Hammett indicator method. The synthesized catalyst exemplified remarkably high atom economy (95%), excellent recyclability (87% after the 10^th cycle), and exceedingly high turnover frequency (TOF), which collectively vouched for this protocol to be reckoned as a greener and more sustainable alternative compared to previously existing methodologies, thereby sharing the podium with some of the best catalysts known for such results.