Knoevenagel-Doebner condensation promoted by chitosan as a reusable solid base catalyst

The development of green and sustainable processes using naturally occurring biopolymers is becoming one of the suitable remedies to replace the conventional catalytic systems that generate large amount of byproducts with high risk factors. In this context, although Knoevenagel-Doebner condensation reaction has been reported with many organocatalysts including proline, no attempts were made to develop heterogeneous catalysts with environmental concerns. Considering these factors in mind, the title reaction is studied with chitosan as a heterogeneous solid base catalyst for the synthesis of alpha,beta-unsaturated carboxylic acids through the condensation followed by decarboxylation reactions. Chitosan offers many advantages including high stability as evidenced by leaching, reusability tests, wide substrate scope and providing higher yields of the desired products with high purity. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscope (SEM) and elemental analysis revealed that there are no major changes in the structural integrity and morphology of chitosan before and after catalysis under the optimized reaction conditions.