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Study of bifunctional acid/base catalysts for aldol condensations · 2017. 3. 12. · J. Lauwaert,...
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Methusalem M2dcR2 Advisory board, Ghent, 19/06/2012 Study of bifunctional acid/base catalysts for aldol condensations J. 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 Technology Krijgslaan 281 (S5), 9000 Ghent, Belgium This work was supported by the ‘Long Term Structural Methusalem Fundig by the Flemish Goverment’ European Research Institute of Catalysis *Center for Ordered Materials, Organometallics & Catalysis, Krijgslaan 281 (S3), 9000 Ghent, Belgium Introduction Aldol condensations: • Create new C-C bonds and yield larger molecules • Are often catalyzed using homogeneous catalysts such as KOH, Ca(OH) 2 , NaOH or Na 2 CO 3 • Are well known in the pharmaceutical industry and the preparation of fine chemicals • Can have a bright future in the valorization of glycerol Synthesis and characterization of the catalysts Aldol condensation experiments Conclusions Proposed reaction mechanism Increasing free silanol to amine ratio • The activity of the amino groups increases with an increasing free silanol to amine ratio Species on the catalyst surface after reaction The surface of the used catalysts has been investigated with Raman spectroscopy and 13 C NMR Three Raman spectra: a) 4-nitrobenzaldehyde adsorbed on silica (silanol – amine ratio = 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 13 C NMR): a) imine; b) c=c bound conjugated with an aromatic ring • Primary amines give a certain basic activity which can be enhanced by incorporating silanol groups in the catalyst • Two components were identified on the surface of the catalyst using Raman spectroscopy and 13 C NMR • A new reaction mechanism is proposed Future work • The dataset will be expanded • The experimental data and the proposed reaction mechanism will be used for microkinetic modeling Aldol Unsaturated ketone Carbinolamine Imine Enamine Grafting with APTES Grafting with HMDS • The grafting is checked with Diffuse Reflectance Infrared Fourier Transform (DRIFT) • The amounts of amines and removed silanol groups are determined using elemental analysis (CHNS analysis) Kieselgel 60 • Catalysts with different free silanol to amine ratios were tested in the aldol condensation of 4-nitrobenzaldehyde with acetone Aldol Unsaturated keton -H 2 O A new reaction mechanism based upon the presence of the components on the surface of the catalyst is proposed
Transcript of Study of bifunctional acid/base catalysts for aldol condensations · 2017. 3. 12. · J. Lauwaert,...
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
