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Phosphorous-doped graphitic material as a solid acid catalyst for microwave-assisted synthesis of β-ketoenamines and baeyer-villiger oxidation
, Maity S., Ram F.
Published in American Chemical Society
Volume: 5
Issue: 26
Pages: 15962 - 15972
Synthesis of phosphorous-doped graphitic materials (P-Gc) using phytic acid as a precursor was done in a microwave oven in a cost- and time-effective green way. The material was used as a solid acid catalyst for microwave (MW)-assisted synthesis of β-ketoenamines and Baeyer-Villiger (BV) oxidation. In the case of BV oxidation, hydrogen peroxide (H2O2) was used as a green oxidant. For β-ketoenamines, in most cases, 100\% conversion with an ∼95\% yield was achieved in ethyl acetate medium. In solventfree conditions, the yield of β-ketoenamines was ∼75\%. A kinetic study suggested that the resonance stabilization of the positive reaction center happens in the transition state for β-ketoenamine synthesis. In BV oxidation, cyclic ketones were converted to their corresponding cyclic esters in good to high yields (∼80\% yield) in a shorter reaction time (6-20 min). As per our knowledge, this is the first report of BV oxidation catalyzed by a heteroatom-doped graphitic material. For BV oxidation, the phosphoric acid functional groups present in P-Gc might increase the electrophilicity of the carbonyl group of the ketones to compensate for the weakness of H2O2 as a nucleophile and a spiro-bisperoxide intermediate has been identified in high-resolution mass spectrometry. © 2020 American Chemical Society.
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