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: jeroen.lauwaert@UGent.be

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