Oxidation of Citronellal to Citronellic Acid by Molecular Oxygen Using Supported Gold Catalysts

✍ Scribed by A. Martin; U. Armbruster; D. Decker; T. Gedig; A. Köckritz

• Publisher: Wiley (John Wiley & Sons)
• Year: 2008
• Tongue: English
• Weight: 241 KB
• Volume: 1
• Category: Article
• ISSN: 1864-5631
• DOI: 10.1002/cssc.200700140

✦ Synopsis

Abstract

The oxidation of citronellal to citronellic acid was studied using molecular oxygen as oxidant and gold‐containing supported catalysts under aqueous conditions. The reactions were carried out at 60–90 °C, with 200 Nml min^−1^ O~2~ and at pH values from 9 to 12. The alumina‐ or titania‐supported catalysts were synthesized according to the deposition–precipitation procedure using urea or NaOH. Mechanistic studies have revealed that radical‐initiated reactions lead to undesired by‐products especially at pH<9, that is, the CC bond is attacked and a diol is primarily formed probably via an epoxide intermediate. This side reaction can be suppressed to a large extent by increasing the pH to 12 and by raising the catalyst/oxygen ratio. Furthermore, detailed studies on the influence of reaction time, pH value, reactant concentration and amount of catalyst show that citronellic acid can be obtained in over 90 % yield with total conversion of citronellal at pH 12 and a temperature of 80 °C.