Hybrid Alginate–Brushite Beads Easily Catalyze the Knoevenagel Condensation On-Water

Abstract

An innovative hybrid organic–inorganic material composed of alginate–brushite xerogel beads was successfully applied for the catalysis of the Knoevenagel condensation. The catalyst was derived from phosphated alginate xerogel microspheres formed from the ionotropic gelling effect of phosphated alginate. To this end, alginate was phosphated by the addition of diammonium hydrogen phosphate in a 1% w/w alginate gel. The phosphated alginate was subsequently precipitated by chelation of Ca 2+ cations, generating a phosphated alginate hydrogel microsphere, which was washed and dried, forming hybrid organic–inorganic xerogel beads as a crystalline phosphate-rich mineral fraction covered by alginate. X-ray diffraction analysis revealed that the crystalline inorganic matrix of the material was composed predominantly of brushite. SEM analysis revealed plate-like, ribbon-like, or needle-like morphologies in the hybrid alginate–brushite beads. The hybrid material was tested as a catalyst for Knoevenagel condensation, which was performed ″on-water″ under mild conditions with aromatic aldehydes and activated methylene compounds, giving high yields (up to 97%). The reaction rate and product yield increased together with the reaction temperature for all reagents. The recyclable solid catalyst was effective for three runs, revealing the potential of the innovative hybrid catalyst as an eco-friendly heterogeneous catalyst.

Mechanistic Insights into the Selective Synthesis of 4H-Pyran Derivatives On-Water Using Naturally Occurring Alginate from Sargassum muticum: Experimental and DFT Study

“…To demonstrate the formation of the RC, benzaldehyde was reacted with SA at room temperature, and then an FTIR spectrum was performed. The analysis of the characteristic bond of the benzaldehyde, C=O functional group, indicates a decrease in the value of this bond from 1694 to 1672 cm −1 , confirming the modification in double bond nature, and an activated carbonyl was formed ( Figure 4 and Figure S10 ) [ 45 , 46 , 47 ]. Moreover, a non-covalent analysis (NCI) was performed on RC intermediate to identify the interactive nature between benzaldehyde and SA (see Figure S11 in SI ).…”

Easily deposited ZnO nanorods on siloxene nanosheets: investigation of morphological, dielectric, ferroelectric, and energy storage properties

“…As previously mentioned, ZnO as an abundant and eco-friendly material, offers versatile nanostructural forms with excellent chemical stability and unique properties for applications in several field, including nanobiotechnology, 28 photocatalysis, 29,30 solar cells, 31,32 piezoelectric devices, 33 and so on. The morphology of ZnO nanostructures varies depending on the synthesis method, precursor, and reaction conditions.…”