Preparation And Application Of Water-soluble Macromolecular Catalyst Containing TEMPO

2,2,6,6-Tetramethylpiperidine-1-oxyl radical?TEMPO?,as a stable radical,is an efficient selective oxidation catalyst.It can not only selectively oxidize small molecular alcohols,but also selectively oxidize the C6 primary hydroxyl groups of cellulose to carboxyl groups to produce oxidized cellulose.However,TEMPO is expensive and toxic,which can be overcome by loading TEMPO on polymer carriers for recycling.Cellulose is a water-insoluble polymer.However,TEMPO-mediated oxidation of cellulose is usually carried out in water.The contact of water-insoluble polymer carrier with cellulose will have a large steric hindrance,which greatly reduces the catalytic oxidation performance.Therefore,it is necessary to prepare water-soluble supported TEMPO catalytic system to improve the catalytic performance of cellulose oxidation in aqueous medium.In this work,three water-soluble polymers were selected as carriers to prepare water-soluble macromolecular TEMPO catalysts,and their catalytic properties for oxidation of benzyl alcohol and cellulose were studied.Firstly,polyacrylamide was prepared by polymerization of acrylamide and then degraded by Hofmann reaction to prepare polyvinylamine.The polyvinylamine-supported TEMPO macromolecular catalysts?P?AM-co-VAm-T??was obtained by the condensation and reduction reaction between polyvinylamine and 4-O-TEMPO.P?AM-co-VAm-T?was used as catalyst to selectively oxidize benzyl alcohol and its catalytic performance was equivalent to 96%of free TEMPO.It was further applied to the selective catalytic oxidation of cellulose and achieve 76%of free TEMPO level.The higher the TEMPO grafting rate,the better catalytic performance of P?AM-co-VAm-T?.The catalyst recycling was achieved by circulating the supernatant and the circulation performance was good.Next,in order to facilitate the recovery of the water-soluble macromolecular catalyst,the temperature-sensitive polymer-supported catalytic system of P?NIPAM-co-TAM?was prepared.The monomer of AATP was prepared by the reaction of acryloyl chloride with2,2,6,6-tetramethylpiperidine,AATP was copolymerized with N-isopropylacrylamide to obtain a random copolymer of P?NIPAM-co-AATP?.The temperature sensitive nitroxide random copolymer of P?NIPAM-co-TAM?was prepared by oxidation of P?NIPAM-co-AATP?.It was applied as catalyst to selective catalytic oxidation of benzyl alcohol with 98.5%of the TEMPO level.When applied to selective oxidation of cellulose,its catalytic effect only reached 20%of free TEMPO level.Finally,in order to balance the easy recovery and high catalytic performance,a water-soluble polyacrylic acid-supported TEMPO catalytic system of P?AA-co-TA?with pH responsiveness was prepared.Partial acylation of polyacrylic acid by SOCl₂ afforded P?AA-co-AC?,which reacted with hydroxyl group in 4-OH-TEMPO to give P?AA-co-TA?.P?AA-co-TA?was used to oxidize benzyl alcohol and reached 90%of the catalytic level of free TEMPO.The selective catalytic oxidation of cellulose showed that the catalytic performance increased when the grafting rate of TEMPO increased from 12.8%to 26.5%.Further increasing the TEMPO grafting rate,the catalytic effect began to decline.The carboxyl group content of the oxidized cellulose was up to 60%of TEMPO level.P?AA-co-TA?was separated from the reaction system by ion exchange method and pH adjusting method.It was continued to be recycled as catalyst and no significant decrease in catalytic performance was found after 4 recycling cycles.