Oxidation of Styrylpyridinium Dyes by Permanganate Ion

Article abstract of DOI:10.1246/bcsj.67.3289

The oxidation of N-alkyl substituted styrylpyridinium bromides in both KMnO4 and cetyltrimethylammonium permanganate (CTAP) results in the formation of corresponding substituted benzaldehydes. The oxidation in aqueous medium is catalyzed by acid whereas in chloroform medium the reaction proceeds at neutral condition. However, the reaction proceeds through the same mechanism in both the media. The faster rate of oxidation in aqueous medium by KMnO4 than that in chloroform medium by CTAP has been rationalized through hydrophobic effect. The overall rate equation can be represented as rate = k^1.5-0.75 in aqueous medium and rate = k^0.5-1 in chloroform medium. From the substituent effect a transition state with low electron density at the olefinic carbon has been proposed.