The Role of Hydroxyl Group Acidity on the Activity of Silica‐Supported Secondary Amines for the Self‐Condensation of n‐Butanal

Abstract

The catalytic activity of secondary amines supported on mesoporous silica for the self-condensation of n-butanal to 2-ethylhexenal can be altered significantly by controlling the Brønsted acidity of M--OH species present on the surface of the support. In this study, M--OH (M=Sn, Zr, Ti, and Al) groups were doped onto the surface of SBA-15, a mesoporous silica, prior to grafting secondary propyl amine groups on to the support surface. The catalytic activity was found to depend critically on the synthesis procedure, the nature and amount of metal species introduced and the spatial separation between the acidic sites and amine groups. DFT analysis of the reaction pathway indicates that, for weak Brønsted acid groups, such as Si--OH, the rate-limiting step is C--C bond formation, whereas for stronger Brønsted acid groups, such as Ti and Al, hydrolysis of iminium species produced upon C--C bond formation is the rate-limiting step. Theoretical analysis shows further that the apparent activation energy decreases with increasing Brønsted acidity of the M--OH groups, consistent with experimental observation.

Fabrication of large-pore mesoporous Ca-Si-based bioceramics for bone regeneration

“…Therefore, LPMSC-1 and LPMSC-2 could bind rhPDGF-BB via hydrogen bonds. [26][27][28][29] However, there was no Si-OH on the surface because LPMSC-3 was completely transformed…”

New Members of the National Academy of Sciences New Fellows of the Royal Society

“…Head‐Gordon’s research involves the development and application of electronic structure theory methods for molecular systems, in particular linear scaling algorithms, widely used density functionals, and a range of correlated wavefunction methods. He is co‐author of a report in ChemSusChem on the activity of silica‐supported secondary amines 4 …”

Neue Mitglieder der National Academy of Sciences Neue Fellows der Royal Society

“…In seiner Forschung befasst er sich mit der Entwicklung und Anwendung von theoretischen Methoden zur Behandlung der elektronischen Struktur von Molekülen, vor allem von Algorithmen zur linearen Skalierung, breit eingesetzten Dichtefunktionalen und einer Vielzahl korrelierter Wellenfunktionen. Er hat eine Veröffentlichung in ChemSusChem über die Aktivität sekundärer Amine auf Kieselgelträgern mitverfasst 4 …”