Knoevenagel condensation reaction on a new highly-efficient La2O2CO3-TiO2 mixed oxide catalyst: Composition-effects on C C bond formation

Calcium single atoms stabilized by nitrogen coordination in metal-organic frameworks as efficient solid base catalysts

Considerable attention has been paid to the preparation of single-atom solid base catalysts (SASBCs) owing to their high activity and maximized utilization of basic sites. At present, the reported fabrication methods of SASBCs, such as two-step reduction strategy and sublimation capture strategy, require high temperature. Such a high activation temperature is easy to cause the sublimation loss of alkali or alkaline earth metal atoms and destructive to the support structure. Herein, a new SASBC, Ca1/UiO-67-BPY, is fabricated, in which the alkaline earth metal Ca sites are immobilized onto N-rich metal-organic framework UiO-67-BPY at room temperature. The results show that the atomic configuration of Ca single atoms is coordinated by two N atoms in the framework. The obtained Ca SASBC possesses ordered structure and exhibits high product yield of 87.2% in the Knoevenagel reaction between benzaldehyde and malononitrile. Furthermore, thanks to the Ca single atoms sites anchored on UiO-67-BPY, the Ca1/UiO-67-BPY catalyst also shows good stability during cycles. This work might offer new insight in designing SASBCs for different base-catalyzed reactions.

Ag@TiO2 Nanocomposite as an Efficient Catalyst for Knoevenagel Condensation

In the present study, a new series of different heterocycles was synthesized through base-free Knoevenagel condensation of various aldehydes and active methylene-containing compounds using the hydrothermal developed Ag@TiO₂ as a heterogeneous catalyst. The catalyst was synthesized by mixing TiO₂ (P25) with AgNO₃ and hydrothermally treated in ethanol at 180 °C for 12 h. The developed Ag@TiO₂ catalyst was directly applied for Knoevenagel condensation, and the optimized procedure involved stirring the aldehydes and active methylene-containing compounds with Ag@TiO₂ in ethanol at 65 °C. The reaction scope was investigated for various aromatic and heterocyclic aldehydes with active methylene-containing compounds, and the isolated yields were significantly high. The reusability of the catalyst was investigated for up to five cycles, where an insignificant decrease in the catalyst's reactivity was observed. Also, the reaction could proceed in water as a solvent, and the isolated yield was 40%. Hence, this protocol features mild reaction conditions, a facile procedure, and clean reaction profiles.

An Overview of Metal-free Sustainable Nitrogen-based Catalytic Knoevenagel Condensation Reaction ‎

Knoevenagel condensation reaction counts as a vital condensation in organic chemistry due to the synthesis of valuable intermediates, ‎heterocycles, and fine chemicals from commercially available reactants through forming new C=C...