Molecular Dynamics Simulations of Aldol Condensation Catalyzed by Alkylamine-Functionalized Crystalline Silica Surfaces

Molecular dynamics simulations are performed to investigate the cooperatively catalyzed aldol condensation between acetone and 4-nitrobenzaldehyde on alkylamine (or alkylenamine)-grafted silica surfaces, focusing on the mechanism of the catalytic activation of the acetone and 4-nitrobenzaldehyde by...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2016-06, Vol.138 (24), p.7664-7672
Main Authors: Kim, Ki Chul, Moschetta, Eric G, Jones, Christopher W, Jang, Seung Soon
Format: Article
Language:English
Subjects:
Aldol condensation
Aldol reactions
Alkylamine catalysis
Amines
Catalytic activity
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
Ketones
MATHEMATICS AND COMPUTING
Molecular dynamics simulation
NANOSCIENCE AND NANOTECHNOLOGY
Silica
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Summary:Molecular dynamics simulations are performed to investigate the cooperatively catalyzed aldol condensation between acetone and 4-nitrobenzaldehyde on alkylamine (or alkylenamine)-grafted silica surfaces, focusing on the mechanism of the catalytic activation of the acetone and 4-nitrobenzaldehyde by the acidic surface silanols followed by the nucleophilic attack of the basic amine functional group toward the activated reactant. From the analysis of the correlations between the catalytically active acid–base sites and reactants, it is concluded that the catalytic cooperativity of the acid–base pair can be affected by two factors: (1) the competition between the silanol and the amine (or enamine) to form a hydrogen bond with a reactant and (2) the flexibility of the alkylamine (or alkylenamine) backbone. Increasing the flexibility of the alkylamine facilitates the nucleophilic attack of the amine on the reactants. From the molecular dynamics simulations, it is found that C3 propylamine and C4 butylamine linkers exhibit the highest probability of reaction, which is consistent with the experimental observation that the activity of the aldol reaction on mesoporous silica depends on the length of alkylamine grafted on the silica surface. This simulation work serves as a pioneering study demonstrating how the molecular simulation approach can be successfully employed to investigate the cooperative catalytic activity of such bifunctional acid–base catalysts.
ISSN:0002-7863
1520-5126
DOI:10.1021/jacs.6b03309