Methusalem M2dcR2 Advisory board, Ghent, 19/06/2012
Study of bifunctional acid/base catalysts for aldol condensationsJ. Lauwaert, E. De Canck*, D. Esquivel*, P. Van Der Voort*, J. Thybaut, G. Marin
http://www.lct.UGent.be E-mail: [email protected]
Laboratory for Chemical TechnologyKrijgslaan 281 (S5), 9000 Ghent, Belgium
This work was supported by the ‘Long Term Structural MethusalemFundig by the Flemish Goverment’
European Research Institute of Catalysis
*Center for Ordered Materials, Organometallics & Catalysis, Krijgslaan 281 (S3), 9000 Ghent, Belgium
Introduction
Aldol condensations:• CreatenewC-C bondsandyield larger molecules• Are oftencatalyzedusinghomogeneous catalystssuchas KOH,
Ca(OH)2, NaOHor Na2CO3
• Are well known in the pharmaceutical industry and thepreparationof fine chemicals
• Canhavea bright futurein thevalorization of glycerol
Synthesis and characterization of the catalysts
Aldol condensationexperiments
Conclusions
Proposed reaction mechanism
Increasing free silanolto amine ratio
• Theactivity of theaminogroups increases withan increasingfreesilanol toamineratio
Species on the catalyst surface after reaction
The surfaceof the usedcatalysts has beeninvestigatedwith Ramanspectroscopyand13C NMR
Three Raman spectra:a) 4-nitrobenzaldehyde adsorbed on silica (silanol – amineratio = 2.2);b) catalyst (silanol – amine ratio = 2.2) after reaction;c) catalyst (silanol – amine ratio = 0) after reaction
Species on the catalyst (confirmed by 13C NMR):a) imine;b) c=c bound conjugated with an aromatic ring
• Primaryamines givea certainbasicactivity which canbeenhancedby incorporatingsilanol groups inthecatalyst
• Two components wereidentifiedon thesurfaceof thecatalyst usingRamanspectroscopyand13C NMR
• A newreactionmechanismis proposed
Future work
• Thedataset will beexpanded• Theexperimental dataandtheproposedreactionmechanismwill be
usedfor microkineticmodeling
AldolUnsaturatedketone
Carbinolamine Imine
Enamine
Grafting with APTES
Grafting with HMDS
• The grafting is checked with Diffuse Reflectance InfraredFourier Transform (DRIFT )
• The amounts of amines andremoved silanol groups aredeterminedusingelemental analysis (CHNSanalysis)
Kieselgel 60
• Catalysts withdifferent free silanol toamine ratios weretestedin the aldol condensationof 4-nitrobenzaldehyde withacetone
Aldol Unsaturated keton
- H2O
A new reactionmechanismbaseduponthe presenceofthe components on thesurface of the catalyst isproposed