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A comprehensive model for the role of water and silanols in the amine catalyzed aldol reaction

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Abstract
The experimentally observed effects of water, and the effects of silanol groups, on the liquid-phase amine-catalyzed aldol reaction of acetone with 4-nitrobenzaldehyde have been elucidated with a comprehensive theoretical model describing the reaction kinetics. The CBS-QB3 model chemistry is used, with bulk solvent effects accounted for according to COSMO-RS theory, and water molecules explicitly considered. Two promoting water molecules were found to be optimal in reducing the Gibbs free energy barriers for reactions involving a proton transfer, i.e., the carbinolamine and enamine formation steps, and the aldol product liberation step. The presence of one water molecule in the carbon-carbon coupling step was already sufficient to prevent the formation of a site-blocking enamine species, which would otherwise lead to deactivation of the amine. Compared to a single water molecule, isolated silanol groups were found to assist the amine in a similar and slightly more pronounced manner, resulting in overall lower barriers for all transition states. Promotion by two vicinal silanols resulted in even lower barriers. The effect of water was found to be more pronounced in apolar hexane as compared to DMSO, i.e., resulting in a less pronounced deactivation of the amine, and lower barriers for reactions where water is assisting in the transition state.
Keywords
Industrial and Manufacturing Engineering, General Chemistry, General Chemical Engineering, Environmental Chemistry, Aldol reaction, Acid-base catalysis, Water effect, Silanol promotion, Solvent effects, AB-INITIO CALCULATIONS, MESOPOROUS SILICA, HETEROGENEOUS CATALYSTS, CARBINOLAMINE FORMATION, ISOLATED HYDROXYLS, CONDENSATION, SURFACE, DIMETHYLAMINE, ARRANGEMENT, GEOMETRIES

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MLA
De Vylder, Anton, et al. “A Comprehensive Model for the Role of Water and Silanols in the Amine Catalyzed Aldol Reaction.” CHEMICAL ENGINEERING JOURNAL, vol. 404, 2021, doi:10.1016/j.cej.2020.127070.
APA
De Vylder, A., Lauwaert, J., Sabbe, M., Reyniers, M.-F., De Clercq, J., Van Der Voort, P., & Thybaut, J. (2021). A comprehensive model for the role of water and silanols in the amine catalyzed aldol reaction. CHEMICAL ENGINEERING JOURNAL, 404. https://doi.org/10.1016/j.cej.2020.127070
Chicago author-date
De Vylder, Anton, Jeroen Lauwaert, Maarten Sabbe, Marie-Françoise Reyniers, Jeriffa De Clercq, Pascal Van Der Voort, and Joris Thybaut. 2021. “A Comprehensive Model for the Role of Water and Silanols in the Amine Catalyzed Aldol Reaction.” CHEMICAL ENGINEERING JOURNAL 404. https://doi.org/10.1016/j.cej.2020.127070.
Chicago author-date (all authors)
De Vylder, Anton, Jeroen Lauwaert, Maarten Sabbe, Marie-Françoise Reyniers, Jeriffa De Clercq, Pascal Van Der Voort, and Joris Thybaut. 2021. “A Comprehensive Model for the Role of Water and Silanols in the Amine Catalyzed Aldol Reaction.” CHEMICAL ENGINEERING JOURNAL 404. doi:10.1016/j.cej.2020.127070.
Vancouver
1.
De Vylder A, Lauwaert J, Sabbe M, Reyniers M-F, De Clercq J, Van Der Voort P, et al. A comprehensive model for the role of water and silanols in the amine catalyzed aldol reaction. CHEMICAL ENGINEERING JOURNAL. 2021;404.
IEEE
[1]
A. De Vylder et al., “A comprehensive model for the role of water and silanols in the amine catalyzed aldol reaction,” CHEMICAL ENGINEERING JOURNAL, vol. 404, 2021.
@article{8677482,
  abstract     = {{The experimentally observed effects of water, and the effects of silanol groups, on the liquid-phase amine-catalyzed aldol reaction of acetone with 4-nitrobenzaldehyde have been elucidated with a comprehensive theoretical model describing the reaction kinetics. The CBS-QB3 model chemistry is used, with bulk solvent effects accounted for according to COSMO-RS theory, and water molecules explicitly considered. Two promoting water molecules were found to be optimal in reducing the Gibbs free energy barriers for reactions involving a proton transfer, i.e., the carbinolamine and enamine formation steps, and the aldol product liberation step. The presence of one water molecule in the carbon-carbon coupling step was already sufficient to prevent the formation of a site-blocking enamine species, which would otherwise lead to deactivation of the amine. Compared to a single water molecule, isolated silanol groups were found to assist the amine in a similar and slightly more pronounced manner, resulting in overall lower barriers for all transition states. Promotion by two vicinal silanols resulted in even lower barriers. The effect of water was found to be more pronounced in apolar hexane as compared to DMSO, i.e., resulting in a less pronounced deactivation of the amine, and lower barriers for reactions where water is assisting in the transition state.}},
  articleno    = {{127070}},
  author       = {{De Vylder, Anton and Lauwaert, Jeroen and Sabbe, Maarten and Reyniers, Marie-Françoise and De Clercq, Jeriffa and Van Der Voort, Pascal and Thybaut, Joris}},
  issn         = {{1385-8947}},
  journal      = {{CHEMICAL ENGINEERING JOURNAL}},
  keywords     = {{Industrial and Manufacturing Engineering,General Chemistry,General Chemical Engineering,Environmental Chemistry,Aldol reaction,Acid-base catalysis,Water effect,Silanol promotion,Solvent effects,AB-INITIO CALCULATIONS,MESOPOROUS SILICA,HETEROGENEOUS CATALYSTS,CARBINOLAMINE FORMATION,ISOLATED HYDROXYLS,CONDENSATION,SURFACE,DIMETHYLAMINE,ARRANGEMENT,GEOMETRIES}},
  language     = {{eng}},
  pages        = {{13}},
  title        = {{A comprehensive model for the role of water and silanols in the amine catalyzed aldol reaction}},
  url          = {{http://dx.doi.org/10.1016/j.cej.2020.127070}},
  volume       = {{404}},
  year         = {{2021}},
}

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