Reconstructed Hydrotalcite as a Highly Active Heterogeneous Base Catalyst for Carbon-Carbon Bond Formations in the Presence of Water
Kohki Ebitani, Ken Motokura, Kohsuke Mori, Tomoo Mizugaki and Kiyotomi Kaneda*
*Department of Materials Engineering Science, Graduate School of Engineering
Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan, Email:
kanedacheng.es.osaka-u.ac.jp
K. Ebitani, K. Motokura, K. Mori, T. Mizugaki, K. Kaneda, J. Org. Chem., 2006, 71, 5440-5447.
DOI: 10.1021/jo060345l
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Abstract
Aldol, Knoevenagel, and Michael reactions of carbonyl compounds are efficiently catalyzed in the presence of water by reconstructed hydrotalcites as solid base catalysts, obtained by treating Mg-Al mixed oxide with water. Reconstructed hydrotalcites provide a unique acid-base bifunctional surface.
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Details
The study explores the use of reconstructed hydrotalcites (HTs) as highly active heterogeneous base catalysts for carbon-carbon bond formations, specifically aldol, Knoevenagel, and Michael reactions, in the presence of water. Reconstructed HTs are prepared by treating Mg-Al mixed oxides with water, creating surface hydroxyl anions that act as base sites. These catalysts offer an environmentally friendly alternative to traditional bases like NaOH and KOH, which are harmful and difficult to recover. The research demonstrates that reconstructed HTs efficiently catalyze aldol reactions of aldehydes, yielding high amounts of β-hydroxy carbonyl compounds without dehydration. The catalysts also promote Knoevenagel and Michael reactions of nitriles with carbonyl compounds, showcasing their acid-base bifunctional surface. The study highlights the importance of water in maintaining the catalytic activity of HTs and discusses the mechanism involving surface OH- species and Lewis acid sites. The reconstructed HTs exhibit a narrow base strength range, making them effective for selective carbon-carbon bond formations. The catalysts are reusable, maintaining high activity and selectivity, and offer a promising approach for green chemistry applications in fine chemical and pharmaceutical syntheses.
T. Hara, S. Kanai, K. Mori, T. Mizugaki, K. Ebitani, K. Jitsukawa, K. Kaneda, J. Org. Chem., 2006, 71, 7455-7462.
Key Words
Aldol Addition, Knoevenagel Condensation, Michael Addition
ID: J42-Y2006-2030