Quitosana-EDTA como catalisador heterogeneizado bifuncional para a reação de condensação de Knoevenagel

Abstract

The Knoevenagel condensation reaction is known in Organic Chemistry as an efficient reaction for the synthesis of new C-C bonds, being originally catalyzed in a homogeneous medium. However, the growing search for less polluting systems has provided the expansion of the production of easily separated catalysts, such as heterogeneous or heterogenized. In this context, chitosan has shown to be very promising for the immobilization of several molecules for use in heterogeneous catalysis. It is already known that chitosan functionalized with EDTA is an excellent adsorbent of transition metals and rare earth ions in the treatment of effluents, but its use as a catalyst is still little explored. Thus, chitosan with low molecular weight (QPB) and medium (QPM) was modified with EDTA and applied to the Knoevenagel reaction as a bifunctional heterogenized catalyst at room temperature between various aldehydes/ketones and active methylene compounds. QPB, QPM, QPB-EDTA-24h, QPM-EDTA-24h, and QPBEDTA-72h were characterized by infrared absorption spectroscopy, powder X-ray diffraction, thermogravimetric analysis, and differential thermal analysis. The estimation of the amount of EDTA functionalized to chitosan was performed indirectly through an adapted method of UVVis absorption spectrophotometry using ninhydrin. This, in turn, showed that QPB-EDTA-72h presents a greater amount of functionalized EDTA at the polymer surface than the others synthesized, indicating that the longer functionalization time increases the number of modified amino groups. In addition, QPB-EDTA-72h enabled the completion of the reaction in short times (0.5-120 min) with good isolated yields (78-98%), being recovered and reused for 6 cycles. In general, QPB-EDTA-72h presented itself as a good reusable bifunctional heterogenized catalyst in the Knoevenagel condensation reaction.