Abstract:

A selective and mild PS-DIB (Diacetoxyiodo polystyrene)/ionic-liquid immobilized TEMPO catalytic oxidation procedure of alcohols to the corresponding aldehydes and ketones in ionic liquid [bmim]BF4 at room temperature was developed. The oxidant PS-DIB was prepared via 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 2,2,6,6-tetramethyl-piperidin-4-ol-N-oxyl (TEMPO) and 1,4-dibromobutane. The TEMPO-IL was then obtained via the quaternization of 1-methyl-1H-imidazole with 4-(2,2,6,6-Tetramethyl-1-oxyl-4-piperidoxyl)butyl bromide followed by ion exchange with NaBF4. The PS-DIB/TEMPO-IL catalytic system applied to the oxidation of a variety of alcohols to the corresponding aldehyde 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 were recovered and reused for 5 times with no decreases of benzyl alcohol conversion and product yield.

Key words: polystyrene, task-specific ionic liquids, oxidation, alcohol