Aldol reaction catalyzed by a hydrophilic catalyst in aqueous micelle as an enzyme mimic system

Increased demand for more sustainable materials and chemical processes has tremendously advanced the use of polysaccharides, which are natural biopolymers, in domains such as adsorption, catalysis, and as an alternative chemical feedstock. Among these biopolymers, the use of chitosan, which is obtained by deacetylation of natural chitin, is on the increase due to the presence of amino groups on the polymer backbone that makes it a natural cationic polymer. The ability of chitosan-based materials to form open-network, macroporous, high-surface-area hydrogels with accessible basic surface sites has enabled their use not only as macrochelating ligands for active metal catalysts and as a support to disperse nanosized particles, but also as a direct organocatalyst. This review provides a concise overview of the use of native and modified chitosan, possessing different textural properties and chemical properties, as organocatalysts. Organocatalysis with chitosan is primarily focused on carbon-carbon bond-forming reactions, multicomponent heterocycle formation reactions, biodiesel production, and carbon dioxide fixation through [3+2] cycloaddition. Furthermore, the chiral, helical organization of the chitosan skeleton lends itself to use in enantioselective catalysis. Chitosan derivatives generally display reactivity similar to homogeneous bases, ionic liquids, and organic and inorganic salts. However, the introduction of cooperative acid-base interactions at active sites substantially enhances reactivity. These functional biopolymers can also be easily recovered and reused several times under solvent-free conditions. These accomplishments highlight the important role that natural biopolymers play in furthering more sustainable chemistry.

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“…Multistep synthesis of CS-Proline reported in Ref. [101]. Fmoc-Osu = N-(9-fluorenylmethoxycarbonyloxy)succinimide.…”

Section: Knoevenagel Reactionmentioning

confidence: 99%

“…[101] The multistep synthesis of the modified material is described in Scheme 7 and enables 2 mmol g À1 of proline-tethered chitosan (CS-Proline) to be obtained. This modified organocatalyst was first used for the prototype condensation of nitrobenzaldehyde and cyclohexanone.…”

Section: Knoevenagel Reactionmentioning

confidence: 99%

Chitosan as a Sustainable Organocatalyst: A Concise Overview

Kadib

2014

ChemSusChem

209

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“…The use of the surfactant improved the results (42-95%, 50-88% de, 41-92% ee) due to the formation of an aqueous micelle that acted as a hydrophobic pocket, allowing the solution of the reactants. However the system was not recovered or reused after the reaction [86]. Not only proline and its derivatives have been supported on organic polymeric resins, but also other catalytic moieties have been grafted into them and used under aqueous conditions.…”

Section: Aqueous Aldol Reactions With Supported Organocatalystsmentioning

confidence: 99%

Pursuing Chemical Efficiency by Using Supported Organocatalysts for Asymmetric Reactions under Aqueous Conditions

Guillena

Alonso²,

Baeza³

et al. 2015

COCAT

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Over the past decade, a great effort has been made by the chemical community to improve the efficiency and greenness of reactions. Merging the use of supported and recyclable organocatalysts and aqueous conditions to pursue this goal in the asymmetric synthesis of interesting enantioselective molecules lead to outstanding results in some cases. Progresses in this area also offer the possibility of having even more sustainable processes by implementing these reactions in the large scale production of chiral molecules using automated flow chemistry.

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“…Indeed, it is known that the rates of many chemical reactions involving aromatic substrates can be accelerated by micelles, 11, 12 including the aldol and retro-aldol reactions. 13–16 However, no specific figures for rate accelerations were given in these reports.…”

Section: Introductionmentioning

confidence: 99%

The effect of the hydrophobic environment on the retro-aldol reaction: comparison to a computationally-designed enzyme

et al. 2013

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Recent work on a computationally-designed retroaldolase RA-61 suggested that most of the rate-acceleration brought about by this enzyme was due to non-specific interactions with the aromatic substrate. To provide a benchmark for the role of non-specific interactions in this system, we measured the second-order rate constant for the amine-catalysed retro-aldol reaction of methodol in the presence of non-specific hydrophobic pockets such as micelles. We found that a simple micellar system, that consists of a positively-charged surfactant and a long-chain amine, can accelerate the retro-aldol reaction of methodol by 9,500-fold. This effect rivals the 105-fold rate acceleration of RA-61. Similar results were obtained with BSA used as the catalyst, implying that the retro-aldol reaction of methodol can be greatly accelerated by non-specific hydrophobic pockets that contain an amino group.

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Aldol reaction catalyzed by a hydrophilic catalyst in aqueous micelle as an enzyme mimic system

Cited by 44 publications

References 20 publications

Chitosan as a Sustainable Organocatalyst: A Concise Overview

Chitosan as a Sustainable Organocatalyst: A Concise Overview

Pursuing Chemical Efficiency by Using Supported Organocatalysts for Asymmetric Reactions under Aqueous Conditions

The effect of the hydrophobic environment on the retro-aldol reaction: comparison to a computationally-designed enzyme

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