The Study On The C_acyl-O Bond Activation Reactions Of Esters Catalyzed By Supported Nano Au,Pd Catalysts

Esters,as important fine chemical products and raw materials and intermediates in pharmaceutical industry,are widely used in medicine,food,spices,cosmetics and other fields.Recent studies on C-O bond activation catalyzed by homogeneous transition metals have brought new impetus to the application of esters.However,due to the disadvantages of traditional homogeneous C-O activation catalytic system,such as high toxicity,difficult recovery and easy pollution,the study of heterogeneous catalytic C-O bond activation reaction has profound theoretical significance and application value.In this paper,a variety of supported nano-Au and Pd catalysts were prepared and applied to those two reactions for realize the C_acyl-O bond activation transesterification and Suzuki-Miyaura cross-coupling reaction catalyzed nano-Au,Pd catalysts.1.3 wt%Au/γ-Al₂O₃ was prepared by impregnation-reduction method protected by low concentration lysine.The transesterification of aryl esters with haloalkanes was successfully catalyzed and the corresponding transesterification products were obtained.With the alkyl halides were used as reactants and solvents,K₂CO₃ as base,reaction temperature as 100℃,reaction time as 24 h,yield of transesterification products could reached 99%.The results show that neither electron effect nor steric hindrance can affect the reaction obviously.But aliphatic acid esters can not executing this reaction successfully.The reaction has good functional group tolerance and substrate universality.In addition,the experimental results show that the catalyst has good recyclability.The catalytic activity of 3 wt%Au/γ-Al₂O₃ catalyst decrease 15%after five cycles of recycling.2.The3wt%Pd/γ-Al₂O₃catalystwaspreparedby impregnation-reduction method protected by low-concentration lysine.It was used to catalyze the cross-coupling reaction of Suzuki-Miyaura coupling between esters and phenylboronic acid..The corresponding ketones were obtained in ideal yield.Using 4-methylbenzoic acid-2-pyridyl ester as a substrate,K₃PO₄ as a base,H₂O as additive,toluene as a solvent,the reaction temperature as 120℃,and the reaction time as 48 h,the yield of aryl ketone can reached 88%.The results show that the electron effect will not affect the reaction,but the coordination ability of N in the directing group and the substituent order of the reaction substrate will have partly effect on the reaction.Alkyl boric acid could not executing this reaction.In addition,the prepared 3wt%Pd/γ-Al₂O₃catalyst was recycled eight times to study its reusability.The results show that the prepared 3wt%Pd/γ-Al₂O₃ catalyst has high stability and good recyclability.The reaction has good substrates applicability and is suitable for the Suzuki-Miyaura cross-coupling reaction of 2-pyridyl esters with aryl boric acid.