Sulfonic acid functionalized graphitic carbon nitride as solid acid-base bifunctional catalyst for Knoevenagel condensation and multicomponent tandem reactions

Abstract

Rational design and development of acid–base bifunctional heterogeneous catalysts for organic synthesis is a tough process. A highly efficient, non-toxic, metal-free, low-cost, acid–base bifunctional sulfonated graphitic carbon nitride (S-g-C3N4) catalyst has been developed. The as-synthesized S-g-C3N4 catalyst exhibits high catalytic potential towards Knoevenagel condensation and sequential tandem reactions. The as-synthesized catalyst was developed by sulfonation of graphitic carbon nitride (g-C3N4). The sulfonation leads to surface functionalization of –SO3H groups onto the catalyst surface. These –SO3H groups impart acidic nature to the S-g-C3N4 catalyst along with the preexisting basic nature of the catalyst due to the presence of N-containing moieties. These dual acid–base functionalities behave as active sites for the sequential catalytic reactions to occur. The S-g-C3N4 catalyst exhibits high turnover numbers (TON) and high yields in shorter reaction time at optimum conditions of temperature which demonstrates the high catalytic activity of the S-g-C3N4 nanosheets. The corresponding green metrics parameters were also calculated, in addition to demonstrating the excellent catalyst recyclability and reusability. The as-synthesized S-g-C3N4 catalyst provides a metal-free, sustainable and green approach for utilizing acid–base bifunctional catalysts for sequential organic synthesis.