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ALCOHOL OXIDATION - A COMPARATIVE STUDY OF DIFFERENT CATALYTIC PROCESSES
Citation:
SahleDemessie*, E AND U R. Pillai**. ALCOHOL OXIDATION - A COMPARATIVE STUDY OF DIFFERENT CATALYTIC PROCESSES. Presented at AIChE, San Francisco, CA, 11/16-21/2003.
Description:
Oxidation of alcohols to aldehydes, ketones or carboxylic acids is one of the most desirable chemical transformations in organic synthesis as these products are important precursors and intermediates for many drugs, vitamins and fragrances. Numerous methods are available for alcohol oxidation, however, the development of newer methods and methodologies are gaining much attention currently due to the significance of this reaction. Oxidation over metal catalysts using eco-friendly oxidants such as hydrogen peroxide and molecular oxygen are preferred now for environmental and economical benefits. This presentation describes a comparison of different catalytic process for the alcohol oxidation such as photocatalysis over TiO2 and various metal containing catalysts viz., Fe3+/montmorillonite-K10, vanadium phosphorus oxide (VPO) and Pd/MgO using hydrogen peroxide and molecular oxygen as environmentally benign oxidants.
Selective oxidations of various primary and secondary alcohols were studied in a gas phase photochemical reactor using immobilized TiO2 catalyst at 150-200 oC with an average contact time of 32 sec. The system was found to be specifically suited for the selective oxidation of primary and secondary aliphatic alcohols to their corresponding carbonyl compounds. However, catalyst deactivation due to the surface accumulation of reaction products and high energy costs are the drawbacks of this process. Nevertheless, the catalyst regained its original activity after regeneration by calcining in air for 3 hours at 723 K. Fe3+/montmorillonite-K10 catalyst prepared by ion-exchange method and VPO catalyst were found to be suitable for the liquid phase selective oxidation of secondary alcohols to the corresponding ketones using hydrogen peroxide. Presence of -CH3 group at the -OH bearing carbon was deleterious to the oxidation. Magnesia supported Pd catalyst was found to be a highly active heterogeneous catalyst for the selective oxidation of alcohols to the corresponding carbonyl products using molecular oxygen in the presence of trifluoro toluene in which a variety of activated and non-activated alcohols could be effectively oxidized in the absence of any additives. All the above three catalysts are relatively cheap, can be prepared easily and can be readily separated from the reaction mixture by simple filtration and reused without any appreciable loss of activity and product selectivity. The mechanisms of oxidation of various catalysts are also discussed.