Selective Oxidative Conversion Of Ethyl Lactate,A Biomass Platform Compound

Lactic acid and lactate are important biomass platform compounds.It’s important to develop some efficient catalytic systems to promote the conversion of lactic acid and lactate to high value-added fine chemicals.Selective oxidation of ethyl lactate（EL）is an effective renewable route for preparation ethyl pyruvate（EP）.However,the conversion process is currently overly dependent on high temperature and inorganic polymetallic catalysts,so to explore the efficient catalytic systems under mild conditions is of great research importance.Herein,two novel catalytic systems were designed and developed to promote the conversion of EL to EP efficiently under the mild conditions using O₂ as the oxygen source.（1）Terpyridine vanadium-based complex（VOC）catalysts has been designed and synthesized as the catalyst for thermo-catalytic oxidation of EL to EP.When VOC was calcined at 400℃ and 500℃ respectively in an Ar gas atmosphere,the as-obtained VOC-400 and VOC-500 represent the homogeneous and heterogeneous catalytic systems,respectively.In the homogeneous system using VOC-400,the complete conversion of EL in acetonitrile at 150℃ with 77.4%yield of EP was obtained.In the heterogeneous system using VOC-500,the complete conversion of EL with 70%yield of EP in acetonitrile at 150℃ was obtained.It is worth mentioning that the catalytic activity of VOC-500 was basically unchanged after 10 cycles.Structural characterisation confirmed that the high activity and stability of VOC-500might be due to the confinement of the derived organic carbon skeleton to the active vanadium centers.（2）A mild,low-cost visible photocatalytic reaction system was developed using trace amounts of covalent bromides as photocatalysts.Catalytic performance tests showed that under visible light irradiation,using molecular oxygen as the oxygen source,trace amounts of HBr or N-bromosuccinimide resulted in the complete conversion of EL within 4 hours and near 100%yield of EP.When using air instead of pure oxygen or a 20-fold gram-scale expansion of the reaction,the high yields of over90%of EP could be still obtained.The 40.6%conversion of EL was obtained even under natural sunlight.A possible mechanism for the photocatalytic oxidation reaction of EL is proposed based on the results of controlled experiments and radical trapping experiments.