Knoevenagel condensation

About: Knoevenagel condensation is a research topic. Over the lifetime, 4896 publications have been published within this topic receiving 80618 citations.

Amino-based metal-organic frameworks as stable, highly active basic catalysts

Abstract: Metal-organic frameworks (MOFs) with non-coordinated amino groups, i.e. IRMOF-3 and amino-functionalized MIL-53, are stable solid basic catalysts in the Knoevenagel condensation of ethyl cyanoacetate and ethyl acetoacetate with benzaldehyde. IRMOF-3DEF exhibits activities that are at least as high as the most active solid basic catalysts reported, with a 100% selectivity to the condensation product. For IRMOF-3 samples the catalytic activity correlated with the accessibility of the basic sites. Diffusion limitations could be excluded for this most active catalyst. A new MOF based on the MIL-53 topology and non-coordinated amino groups has been synthesized and characterized. Although active its poor performance in the studied Knoevenagel condensations is attributed to strong adsorption and diffusion limitations in the 1-D pore structure of this framework. The performance of the IRMOF-3 catalysts demonstrates that the basicity of the aniline-like amino group is enhanced when incorporated inside the MOF structure, increasing the pKa of the basic catalyst and more active than aniline as homogeneous catalyst. The IRMOF-3 catalysts are stable under the studied reaction conditions, and could be reused without significant loss in activity. The catalytic performance of IRMOF-3 in various solvents suggests that this open, accessible and well-defined structure behaves more like homogeneous basic catalysts, in contrast to other solid basic catalysts. By means of DRIFTS, the reaction mechanism has been elucidated, showing spectroscopic evidence of benzaldimine intermediates.

Expanding Applications of Metal−Organic Frameworks: Zeolite Imidazolate Framework ZIF-8 as an Efficient Heterogeneous Catalyst for the Knoevenagel Reaction

Abstract: A highly porous zeolite imidazolate framework (ZIF-8) was synthesized by a solvothermal method, and used as an efficient heterogeneous catalyst for the Knoevenagel reaction. The solid catalyst was characterized using a variety of different techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic laser light scattering (DLS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. Quantitative conversion was achieved under mild conditions. The ZIF-8 catalyst could be facilely separated from the reaction mixture, and could be reused without significant degradation in catalytic activity. Furthermore, no contribution from homogeneous catalysis of active species leaching into reaction solution was detected.

3D Microporous Base‐Functionalized Covalent Organic Frameworks for Size‐Selective Catalysis

Abstract: The design and synthesis of 3D covalent organic frameworks (COFs) have been considered a challenge, and the demonstrated applications of 3D COFs have so far been limited to gas adsorption. Herein we describe the design and synthesis of two new 3D microporous base-functionalized COFs, termed BF-COF-1 and BF-COF-2, by the use of a tetrahedral alkyl amine, 1,3,5,7-tetraaminoadamantane (TAA), combined with 1,3,5-triformylbenzene (TFB) or triformylphloroglucinol (TFP). As catalysts, both BF-COFs showed remarkable conversion (96% for BF-COF-1 and 98% for BF-COF-2), high size selectivity, and good recyclability in base-catalyzed Knoevenagel condensation reactions. This study suggests that porous functionalized 3D COFs could be a promising new class of shape-selective catalysts.

Synthesis and characterization of an amino functionalized MIL-101(Al): Separation and catalytic properties

Abstract: A new MIL-101 material based on aluminum and containing amine functional groups has been synthesized. The pure phase NH2-MIL-101(Al) can only be formed in very specific synthesis conditions, where both the metal source and the solvent used play a key role. The resulting porous solid shows a high thermal and chemical stability, decomposing at temperatures above 650 K in air. The NH2-MIL-101(Al) framework offers an excellent trade off for separation of CO2: the combination of high stability, acceptable capacity at low adsorbate partial pressures, high selectivity, and fast regenerability makes this new material a very attractive candidate for applications like natural gas or biogas upgrading. CO2 capacities up to 62 wt % are obtained at room temperature and 3 MPa. In addition to an excellent separation performance, the NH2-MIL-101(Al) shows a high activity in the basic catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 313 K even in an as apolar a solvent as toluene (turn over fre...

ZIF-8: A comparison of synthesis methods

Abstract: A zeolitic imidazolate framework, ZIF-8, was prepared via a variety of synthesis routes: solvothermal, microwave-assisted, sonochemical, mechanochemical, dry-gel, and microfluidic methods. Their textural properties and morphology were examined by surface area measurements and scanning electron microscopy, and compared with those of commercial ZIF-8. Although the BET surface areas fell within a range of 1250–1600 m 2 g − 1 , the particle size of the samples prepared by dry-gel and sonochemical routes were significantly smaller than the others, which led to superior performance in the Knoevenagel condensation reaction. The effective incorporation of magnetic Fe 3 O 4 nanoparticles into the ZIF-8 structure for easy particle separation in the liquid phase was feasible using solvothermal, dry-gel and mechanochemical synthesis methods. Dry-gel and mechanochemical synthesis produced a higher ZIF-8 yield.