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

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 degrees C, with 200 Nml min(-1) O2 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 degrees C.

Novel Design of Citral-Thiourea Derivatives for Enhancing Antifungal Potential against Colletotrichum gloeosporioides

“…The specific synthetic route of the generated targeted compounds is shown in Scheme . The method used was adopted from previous reports. , Briefly, citral was used as the raw material and converted into citronellal through a Pd/TPP hydrogenation reaction. Then, the obtained citronellal was oxidized to citronellic acid (compound b ) by the oxidation reaction.…”

Selectivity of Gold Catalysts for Applications of Commercial Interest

“…In the production of citronellic acid, it has been found that 1 wt% Au/TiO 2 and 1 wt% Au/Al 2 O 3 , made using the DP urea method gave conversions of 97% and 100% (as determined by GC) in aqueous conditions using oxygen at 80°C and pH 9 at atmospheric pressure [11]. Au particle Continuous conversion of glucose to gluconic acid over 110 days using 0.3% Au/Al 2 O 3 , at different retention times and resulting average conversions, adapted from ref.…”

Amine-Functionalized Hydrophobic Cross-Linked Polymer-Supported Palladium Nanoparticles: An Efficient Catalyst for the Selective Hydrogenation of Citral to Citronellal

“…One of the most important products is citronellal (Figure ), which can be used as a key compound in organic synthesis. It can be used as a key intermediate or chiral source in the total synthesis of natural and non-natural compounds such as pheromones and cyclic, polycyclic, and alycyclic compounds. − It can also be used as a raw material for fine commodities in the food, fragrance, cosmetic, and pharmaceutical industries. − …”