Catalysed chromium(VI) oxidations of trans-stilbene

The catalytic activities of 1,10-phenanthroline (Phen), oxalic acid (Oxa) and picolinic acid (PA) in the chromium(VI) oxidation of trans-stilbene to the diketone have been investigated in acidic solutions. The CrVI–Phen/Oxa/PA complex is believed to be the probable reactive electrophile. The available kinetic data very much suggests that the oxidation of trans-stilbene involves the nucleophilic attack of the ethylenic bond on CrVI–Phen/Oxa/PA complex and the formation of a ternary complex can be envisaged. Low dielectric constant of the medium favours the facile complex formation. Contrary to expectation, Mn(II) smoothly catalyses this conversion. Comparison of the catalytic efficiencies of various complexing agents reveals that the effect is more pronounced in the case of oxalic acid catalysis. The mechanistic pathway has been determined based on the detailed kinetic analysis.