The role of hydroxyl group acidity on the activity of silica-supported secondary amines for the self-condensation of n-butanal

Sankaranarayanapillai Shylesh, David Hanna, Joseph Gomes, Christian G. Canlas, Martin Head-Gordon, Alexis T. Bell*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

The catalytic activity of secondary amines supported on meso-porous 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 in-troduced 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.

Original languageEnglish (US)
Pages (from-to)466-472
Number of pages7
JournalChemSusChem
Volume8
Issue number3
DOIs
StatePublished - 2015
Externally publishedYes

Keywords

  • Aldol reaction
  • Amines
  • Mesoporous silica
  • Organocatalysis
  • Titanium

ASJC Scopus subject areas

  • Energy(all)
  • Environmental Chemistry
  • Materials Science(all)
  • Chemical Engineering(all)
  • Medicine(all)

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