Campus Units
Chemistry, Ames Laboratory
Document Type
Article
Publication Version
Submitted Manuscript
Publication Date
5-8-2019
Journal or Book Title
ACS Catalysis
Volume
9
First Page
5574
Last Page
5582
DOI
10.1021/acscatal.9b00195
Abstract
Aminopropyl-functionalized mesoporous silica nanoparticles (AP-MSN) catalyze aldol condensations. The activity of AP-MSN decreases with increasing solvent polarity due to the stabilization of ion pairs formed between acidic silanol groups and the amines, which ultimately decreases the number of catalytically active amine sites. However, the reaction in water is faster than expected based on polarity, because water limits the formation of Schiff bases that are also responsible for blocking active sites. In this work, we combined the action of water with a low-local-polarity environment around the catalytic sites of AP-MSN to maximize active site availability and catalyst performance. We specifically demonstrate how the local polarity of AP-MSN can be controlled by modifying its surface with varying concentrations of hexyl groups, and how the dielectric constant of the silica-water interface can be determined using the solvatochromic probe Prodan. The catalytic activities of hexyl-modified AP-MSN in water were inversely proportional to their interfacial dielectric constants, and were significantly higher (roughly by a factor of 4) than those of AP-MSN in anhydrous solvents of comparable polarities. Producing low-local-polarity environments in aqueous AP-MSN also enhanced the sensitivity of the aldol reaction to the electronic effects of substituents in the substrate. The enhancement of catalytic activity by low interfacial polarity was also observed in other amine-catalyzed C-C bond forming reactions such as the Henry and Vinylogous aldol reactions. Overall, our results demonstrate that the catalytic activity of AP-MSN can be controlled by the synergistic action of water and a low interfacial dielectric constant.
Copyright Owner
American Chemical Society
Copyright Date
2019
Language
en
File Format
application/pdf
Recommended Citation
Singappuli-Arachchige, Dilini; Kobayashi, Takeshi; Wang, Zhuoran; Burkhow, Sadie J.; Smith, Emily A.; Pruski, Marek; and Slowing, Igor I., "Interfacial Control of Catalytic Activity in the Aldol Condensation: Combining the Effects of Hydrophobic Environments and Water" (2019). Chemistry Publications. 1125.
https://lib.dr.iastate.edu/chem_pubs/1125
Comments
This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in ACS Catalysis, copyright © American Chemical Society after peer review. To access the final edited and published work see DOI: 10.1021/acscatal.9b00195. Posted with permission.