Study On The Selective Catalytic Oxidation Of ?-Hydroxy Esters To ?-Keto Esters

Selective catalytic oxidation of?-hydroxy esters to prepare high value-added?-keto esters is one of the most important significance.The efficient catalytic system consisting of Zn?NO₃?₂/VOC₂O₄ and Amberlyst-15/1,3-dibromo-5,5-dimethylhydantoin are reported here for catalytic oxidation of?-hydroxy esters to high yields of?-keto esters by using cheap and environmentally friendly molecular oxygen and hydrogen peroxide as oxidants under mild reaction conditions.In this paper,a new strategy for selective catalytic oxidation of?-hydroxy esters to?-keto esters using VOC₂O₄/Zn?NO₃?₂ with molecular oxygen was reported.Up to 99%conversion of?-hydroxy esters could be facilely obtained with above 95%selectivity for its corresponding?-keto ester under mild reaction conditions?80?,0.2 MPa O₂ 1.5 h or 25?,0.1 MPa O₂ 48-72 h?.The control experiment result of metal nitrates suggested that Zn?NO₃?₂showed the best performance among those metal nitrates tested in this work.The catalytic activity difference of Zn?NO₃?₂ or Fe?NO₃?₃ as catalyst component was then studied.The FT-IR and situ ATR-IR results indicated that the interaction derived from Zn?NO₃?₂ or Fe?NO₃?₃ with VOC₂O₄ respectively was quite different,and different nitric species in vapor phases were generated under this oxidative condition,which was HNO₃ vapor,N₂O₃ and N₂O₄ mixture gas respectively.The XPS spectra suggested that active vanadium?V?species were generated after the interaction of Zn?NO₃?₂/VOC₂O₄,while no active vanadium?V?species were obtained when VOC₂O₄ was reacted with Fe?NO₃?₃ under the same reaction conditions.The ATR-IR and XPS result suggested that HNO₃ gas derived from the interaction of Zn?NO₃?₂ with VOC₂O₄ could be in favor of oxidizing vanadium?IV?to active vanadium?V?species,Thus explaining why Zn?NO₃?₂ combination with VOC₂O₄ exhibited unique catalytic activity,compared with other tested metal nitrates such as Fe?NO₃?₃ under the same reaction conditions.In this paper,another new strategy for selective catalytic oxidation of?-hydroxy esters to?-keto esters using Amberlyst-15/1,3-dibromo-5,5-dimethylhydantoin with hydrogen peroxide was then reported.Up to 99%conversion of?-hydroxy esters could be facilely obtained with above 95%selectivity for its corresponding?-keto ester under mild reaction conditions?25?,8 h?.After 6 runs,the catalytic activity of Amberlyst-15 catalyst remained basically unchanged.Various aromatic alcohols and aliphatic second alcohols undergo selective oxidation to afford the corresponding carbonyl compounds with good or excellent yields using Amberlyst-15/1,3-dibromo-5,5-dimethylhydantoin as catalysts.72-99%conversion of 10 case of alcohols other than 1-pentanol was obtained with 81-99%selectivity for its corresponding ketone,and corresponding plausible catalytic reaction mechanism was proposed.