Preparation Polymerization Of Polyaniline Containing TEMPO And Its Electrochemical Catalytic Activities

Use of the stable nitroxyl radical 2,2,6,6-tetramethylpiperidinloxyl?TEMPO?as an efficient catalyst for alcohol and amine oxidation is highly desirable due to its environmentally friendly and the high selectivities.In order to facilitate the separation and recycling of TEMPO,it needs to perform immobilization.Polyaniline?PAn?is a conducting polymer with unique properties,such as high conductivity,good environmental stability and easy preparation.Therefore,it has been applied to the research of immobilization of TEMPO.In this paper,monomer4-?2-aminobenzoyl-oxy?-2,2,6,6-tetramethylpiperidin-1-yloxy?An-TEMPO?,can be obtained by the ester linkage of methyl anthranilate and 4-hydroxy-TEMPO.Then,its corresponding polyaniline containing TEMPO?PAn-TEMPO?was successfully prepared by electrochemical polymerization.And the electrocatalytic oxidation performance of alcohols and amines is investigated by cyclic voltammetry,in situ FTIR and preparative electrolysis experiments.Firstly,preparation of PAn-TEMPO electrode was carried out in water/acetone solution by electrochemical polymerization of An-TEMPO.Its electrocatalytic activity and the mechanism of oxidation reaction of alcohols were studied by cyclic voltammetry and in situ FTIR.The results showed that the TEMPO⁺was formed by electrochemical one-electron oxidation of TEMPO,then the TEMPO⁺served as a slective oxidizing agent for oxidation alcohols to correspoding aldehydes or ketones.2,6-Lutidine or Na₂CO₃/NaHCO₃ could improve the rate of alcohol consumption to generate aldehydes or ketones.The oxidation reaction of alcohol was mainly carried out on the PAn-TEMPO film instead of the substrate electrode.In addition,various alcohols were efficiently oxidized to their corresponding aldehydes or ketones in water solution by preparative electrolysis experiments.The results showed that the PAn-TEMPO electrode presented high electrocatalytic activity and selectivity for oxidation of alcohols,and the oxidation of aromatic alcohols exhibited better.Secondly,cyclic voltammetry and electrochemical in situ FTIR were applied to study the electrocatalytic activity of amines in different conditions.Results showed that PAn-TEMPO presented high electrocatalytic activity for oxidation of benzylamine,?-phenylethylamine,4-methoxybenzylamine and propylamine.The oxidation product was imine in nonaqueous system.However,the oxidation product was aldehyde in aqueous system.Finally,the PAn-TEMPO/BTh electrode was achieved by electrochemical copolymerization of An-TEMPO and BTh.Its catalytic activity for the oxidation of benzyl alcohol was investigated by cyclic voltammetry combined with in situ FTIR.According to the results,benzyl alcohol was selectively oxidized to benzaldehyde by PAn-TEMPO/BTh electrode.In addition,bithiophene was essential on the polymer film and improved the conductivity of the polymer,which leaded to the PAn-TEMPO/BTh has high electrocatalytic activity.