CATALYTIC OXIDATION OF AROMATIC ALDEHYDES TO CARBOXYLIC ACIDS IN MILD CONDITIONS WITH NaClO2

Abstract

This study aimed to improve the conditions for the oxidation of benzaldehyde to benzoic acid using chlorine dioxide generated from sodium chlorite, across various pH ranges and different catalysts. The powerful oxidation capability of chlorine dioxide played a crucial role in enhancing the kinetic efficiency of the reactions. In our research, we examined various reaction conditions, including sodium dihydrogen phosphate, sodium dihydrogen phosphate together with sodium chlorite, sodium dihydrogen phosphate combined with sodium chlorite and potassium permanganate, and sodium dihydrogen phosphate with sodium chlorite and V2O5. Additionally, different oxidation combinations were tested, such as sodium chlorite with sodium tripolyphosphate (STPP), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), and formic acid, as well. The stabilized chlorine dioxide solution was also used directly as an oxidation reagent. The role of chlorine dioxide in these combinations significantly impacted the selectivity and yield in terms of product. Furthermore, some Mn (III) complexes (Cat.1 and Cat.2) were used as catalysts in this study, and the findings revealed that chlorine dioxide is an effective oxidant in the selective oxidation of aromatic aldehydes to aromatic acids. For the catalytic application in buffer solutions, a leveling effect was observed. When Mn (III) complexes were used, it showed a similar leveling effect in buffer solutions with a pH >1, which was resulting in slow ClO₂ formation. With these findings it was found that the use of Mn (III) complexes in NaH2PO4+NaClO2 combination provided the highest yield in the oxidation of aromatic aldehydes to acids. These results underscore the importance of chlorine dioxide as a powerful oxidant in chemical transformation processes.