Efficient catalytic oxidation of primary benzylic CH bonds with molecular oxygen catalyzed by cobalt porphyrins and N-hydroxyphthalimide (NHPI) in supercritical carbon dioxide

Abstract

The oxidation of benzylic CH bonds by metalloporphyrins in supercritical carbon dioxide (scCO2) has still limited. Herein, an efficient protocol of aerobic oxidation of primary benzylic CH bond by cobalt porphyrin and NHPI (N-hydroxyphthalimide) in scCO2 was established. Using toluene as model substrate, 21.6% conversion and 81.2% benzoic acid selectivity was obtained under the optimized conditions. The protocol also exhibited good tolerance towards the oxidation of various substrates with different electron property groups. Moreover, a plausible mechanism involving free radical and high-valence cobalt species was proposed.

Keywords

• CH bond
• Toluene
• Oxidation
• Cobalt porphyrins
• Supercritical carbon dioxide