Critical assessment of the efficiency of chitosan biohydrogel beads as recyclable and heterogeneous organocatalyst for C–C bond formation

Abstract

The effectiveness of neutral pH chitosan hydrogel beads (CSHB) as a green organocatalyst for a variety of C-C bond forming reactions (i.e. aldol reaction, Knoevenagel condensation, nitroaldol (Henry) reaction, Michael addition) has been comprehensively evaluated. Reaction rates, conversions and selectivities were studied as a function of a series of input variables including size, pH and reactive surface area of the beads, catalyst loading, temperature, molecular weight of the biopolymer, concentration, solvent system and molar ratio of reactants. Moreover, the catalytic biohydrogel beads were characterized by a variety of techniques including, among others, SEM, FT-IR, TGA and DSC.

Keratin Protein-Catalyzed Nitroaldol (Henry) Reaction and Comparison with Other Biopolymers

“…At this point, we carried out kinetic analyses of the model reaction between 1a and 2a catalyzed by keratin in both DMSO and H 2 O/TBAB under the described conditions. The results were compared with the performance of other biopolymers as biocatalysts for the same reaction that we have previously studied in our group and others (i.e., chitosan [18], gelatin [19], collagen [19], bovine serum albumin (BSA) [19,23], silk fibroin [20] and alginate [21]) under optimized conditions. Figure 2 shows the first-order kinetics corresponding to each biopolymer within the first hours of reaction.…”

“…On the other hand, the nitroaldol (Henry) reaction is a highly versatile C-C bond-forming reaction between an aldehyde or ketone and a nitroalkane to yield β-nitroalcohols, which can be easily modified into valuable building blocks [13][14][15][16][17]. As part of one of our research programs devoted to understanding the potential catalytic role of different biopolymers [18][19][20][21], we report here for the first time the catalytic properties of keratin protein towards the nitroaldol (Henry) reaction as well as a critical comparison with the performance of other natural polymers in the same process.…”

“…As part of one of our research programs devoted to understanding the potential catalytic role of different biopolymers [18][19][20][21], we report here for the first time the catalytic properties of keratin protein towards the nitroaldol (Henry) reaction as well as a critical comparison with the performance of other natural polymers in the same process.…”

An Ionic Liquid Solution of Chitosan as Organocatalyst

“…Interestingly, in other studies, where hydrogel beads of chitosan were applied in an Aldol reaction in DMSO, the obtained Aldol product was racemic [13]. A further study with chitosan biohydrogel beads by the group of Diaz Diaz [14], explored several reactions including the Aldol reaction with the heterogeneous catalyst in different solvents such as DMSO and water. No enantiomeric excess was reported.…”

Structurally Complexes Aromatic Aldehydes on Knoevenagel Condensation Catalyzed by Chitosan Hydrogel Beads

“…7 Other interesting applications involve the synthesis of heterocycles such as pyrimidinobenzothiazole. 8 In this communication, we synthesized new Knoevenagel switchable products from malononitrile and highly modified aldehydes owning different steric hindrance and electronic effects.…”