负载型二乙酰氧碘苯与功能离子液体协同氧化醇为醛酮

将聚苯乙烯树脂(PS)先碘化再乙酰基化,制得了负载型二乙酰氧碘苯(PS-DIB)作为氧化剂。2,2,6,6-四甲基-N-氧自由基哌啶醇(TeMPO)与1,4-二溴丁烷反应生成4-溴丁氧基-2,2,6,6-四甲基-哌啶-1-氧化物,再与N-甲基咪唑发生季铵化反应,生成的溴化季铵盐与四氟硼酸钠进行离子交换制得氟硼酸型2,2,6,6-四甲基-N-氧自由基哌啶负载离子液体(TeMPO-IL)。室温下,以离子液体1-甲基-3-丁基咪唑四氟硼酸盐([bmim]BF4)为溶剂,PS-DIB为氧化剂,TeMPO-IL为催化剂,选择性协同氧化各种醇为相应的醛或酮。在实验条件范围内未检测到羧酸副产物。氧化剂、催化剂和溶剂均可循环使用,在苯甲醇的氧化中,循环使用5次,反应的转化率和收率均保持基本不变。

Oxidation of Alcohols to Corresponding Aldehydes and Ketones with Polystyrene-supported Hypervalent Iodine Oxidant and Functional Ionic Liquid

A selective and mild PS-DIB(diacetoxyiodo polystyrene)/ionic-liquid immobilized 2,2,6,6-tetramethyl-piperidin-4-ol-N-oxyl(TeMPO) catalytic oxidation procedure of alcohols to the corresponding aldehydes and ketones in ionic liquid [bmim]BF_4 at room temperature was developed. The oxidant PS-DIB was prepared via the iodation and acetylation of polystyrene resin. For the preparation of the ionic-liquid immobilized TeMPO(TeMPO-IL) catalyst,4-(2,2,6,6-Tetramethyl-1-oxyl-4-piperidoxyl)butyl bromide was first synthesized from TeMPO and 1,4-dibromobutane. The TeMPO-IL was then obtained via the quaternization of 1-methyl-1H-imidazole with TeMPO-IL followed by ion exchange with NaBF_4. The PS-DIB/TeMPO-IL catalytic system was applied to the oxidation of a variety of alcohols to their corresponding aldehydes or ketones selectively. No carboxylic acid was detected under the experimental conditions. In the case of the oxidation of benzyl alcohol,the oxidant,catalyst and the solvent can be recovered and reused for 5 times without decreasing the benzyl alcohol conversions and yields.