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Intraparticle Diffusional versus Site Effects on Reaction Pathways in Liquid-Phase Cross Aldol Reactions
Koushik Ponnuru1, Jinesh C Manayil2, Hong Je Cho1
1Department of Chemical Engineering, University of Massachusetts Amherst, 159 Goessmann Laboratory, 686 N Pleasant, Amherst, MA, 01003, USA.
Summary
Catalyst properties and reaction conditions control chemo- and regioselectivity in cross aldol reactions. Tuning these factors influences product formation, favoring branched aldol products or leading to fission products under specific conditions.
Area of Science:
- Heterogeneous catalysis
- Organic synthesis
- Reaction mechanism
Background:
- Aldol reactions are fundamental in organic synthesis.
- Controlling selectivity in aldol reactions remains a challenge.
- Heterogeneous catalysts offer tunable properties for reaction control.
Purpose of the Study:
- To investigate chemo- and regioselectivity in heterogeneously catalyzed cross aldol reactions.
- To understand the influence of catalyst properties and reaction conditions on product distribution.
- To elucidate the reaction pathways, including aldol addition, condensation, and fission.
Main Methods:
- Utilized sulfonic acid-functionalized resins and SBA-15 materials with varying properties.
- Employed H-BEA zeolites and Sn-BEA zeotype catalysts.
- Conducted reactions under varying temperatures (25–170 °C) in organic media.
- Analyzed product distributions including branched and linear aldol products, condensation products, and fission products.
Main Results:
- Catalyst properties (acidity, textural) and reaction conditions significantly impacted chemo- and regioselectivity.
- Resins and functionalized SBA-15 predominantly yielded branched condensation products.
- Diffusion limitations or high temperatures led to increased fission products (Wheeler Type II selectivity).
- H-form zeolites showed competition between branched aldol fission and linear aldol dehydration, attributed to weaker acidity or steric effects.
Conclusions:
- Catalyst design and reaction engineering are crucial for directing selectivity in cross aldol reactions.
- Understanding the interplay between catalyst properties, reaction conditions, and diffusion is key to optimizing product yields.
- The study provides insights into controlling complex reaction networks involving aldol addition, condensation, and subsequent transformations.
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