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Oxidation of Citronellal to Citronellic Acid by Molecular Oxygen Using Supported Gold Catalysts
Author(s) -
Martin A.,
Armbruster U.,
Decker D.,
Gedig T.,
Köckritz A.
Publication year - 2008
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.200700140
Subject(s) - catalysis , chemistry , citronellal , yield (engineering) , inorganic chemistry , aqueous solution , oxygen , urea , epoxide , organic chemistry , materials science , metallurgy
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 CC 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.