Unprecedented Reductive Esterification of Carboxylic Acids under Hydrogen by Reusable Heterogeneous Platinum Catalysts

• Published in: Advanced synthesis & catalysis 2015-05, Vol.357 (7), p.1499-1506
• Main Authors: Touchy, Abeda S., Kon, Kenichi, Onodera, Wataru, Shimizu, Ken-ichi
• Format: Article
• Language: English
• Subjects: Carboxylic acids; Catalysis; Catalysts; Esters; heterogeneous catalysis; hydrogenation; Platinum; Reusable; tin; Tin dioxide; Tin oxides
• ISSN: 1615-4150; 1615-4169
• DOI: 10.1002/adsc.201401172

Supported metal catalysts have been tested for an unprecedented reductive dimerization of carboxylic acids to esters under 8 bar hydrogen in solvent‐free conditions. Among various metal‐loaded tin oxide catalysts, platinum‐loaded tin dioxide (Pt/SnO2) shows the highest ester yield for the reaction of dodecanoic acid. Among Pt catalysts on various supports, Lewis acidic oxides, especially SnO2, show high activity. The most active catalyst, 5 wt% Pt/SnO2 reduced at 100 °C, is effective for the reductive esterification of various carboxylic acids, and the catalyst is reusable for nine cycles, demonstrating the first successful example for the title reaction. Infrared (IR) studies of a model compound (formic acid) on some metal oxides indicate a strong Lewis acid‐base interaction between SnO2 and the carbonyl oxygen. For Pt/SnO2 catalysts with different Pt particle sizes, the activity increases with decreasing size of Pt metal. A cooperative catalysis of the Pt metal nanoparticles and the Sn4+ Lewis acid sites is proposed.