Insights into Substituent Effects of Benzaldehyde Derivatives in a Heterogeneous Organocatalyzed Aldol Reaction

Abstract

Organocatalyst immobilization onto solid supports represents a promising method for enabling asymmetric organocatalysis while retaining the advantages of heterogeneous catalysts, including catalyst separation, recycling, and the use of fixedbed reactors. Understanding how such heterogenized catalytic systems work is fundamental to develop and tailor more efficient ones. Herein, we have elucidated the role of reactant molecular structure on surface interactions and reactivity for asymmetric aldol reactions between benzaldehyde derivatives and hydroxyacetone catalyzed by SBA-15 immobilized L-proline.NMR relaxation time analysis reveals that a stronger interaction between the aldehyde and the catalyst surface reduces catalytic reactivity, which is attributed to reduced access of hydroxyacetone to the L-proline surface sites, hence inhibiting the formation of the enamine intermediate between hydroxyacetone and L-proline. The results show that surface phenomena in these systems are important considerations for reactant selection, opening up new directions to explore in this area of research.

Humin Formation on SBA-15-pr-SO3H Catalysts during the Alcoholysis of Furfuryl Alcohol to Ethyl Levulinate: Effect of Pore Size on Catalyst Stability, Transport, and Adsorption

“…To further understand the effect of humin deposition on diffusion and adsorption properties within catalysts with different pore sizes, NMR diffusion and relaxation studies were performed. NMR relaxation measurements have previously been demonstrated to be a powerful, nondestructive method to probe the interactions of molecules over surfaces of inorganic/organic heterogeneous catalysts. − In addition, pulsed-field gradient (PFG) NMR experiments can be used to measure diffusion coefficients in a variety of situations, including liquid mixtures, , ionic solvents, liquids imbibed within porous materials, − and to probe accessibility of molecules in pore structures. , …”

Influence of stabilisers on the catalytic activity of supported Au colloidal nanoparticles for the liquid phase oxidation of glucose to glucaric acid: understanding the catalyst performance from NMR relaxation and computational studies

“…74 As such, the T 1 / T 2 ratio can find great use in the field of catalysis and surface science to quantify the strength of surface interactions taking place and explain phenomena such as solvent effects. 75–78…”

Metal-Free Phosphate Modified Hierarchically Porous Carbon–Silica Nanocomposites for Solvent-Free Glycerol Carbonylation and Esterification Reactions

“…Being the trend in recent years in catalysis, it allows reducing the catalyst cost, and it is also desirable to curtail the metal species contamination, which sometimes degrades the product . On the other hand, supported organocatalysts and carbon nitride materials have exhibited promising activity as metal-free catalytic systems. − The metal-free catalysts are being used in diverse fields like biomass transformation, CO 2 conversion, removal of organic pollutant from water, etc. ,− In these contexts, highly porous carbon based materials are a worthy candidate. These materials exhibit a high surface area, large pore sizes, and well-controlled pore apertures.…”