Study On Oxidation Of Alcohols To The Corresponding Carbonylcompounds With Hypervalent Iodine(Ⅲ) Compounds

The oxidation of alcohols to the corresponding carbonylcompounds is one of the most fundamental and important transformations in synthetic organic chemistry. Over the past two decades, hypervalent iodine(III) compounds have been widely used in alcohol oxidation reactions due to their mild, easy preparation and chemoselective oxidizing properties and their environmentally benign character.Oxidation of alcohols with hypervalent iodine(III) reagents in the presence of TEMPO as a catalyst was studied in this paper.4-Nitrophenyl methanol can be oxidized to 4-nitrobenzaldehyde in 93% yield with 1.1 equivalent of PhI(OAc)2 and 0.1 equivalent of 4-OH-TEMPO in AcOH at room temperature for 2 hours. The scope of the reaction was then tested. A series of benzyl alcohols, allyl alcohols, naphthene alcohols, heterocyclic alcohols and aliphatic alcohols were oxidized to the correspongding aldehydes and no acid was detected in all cases.Poly[4-(diacetoxyiodo)styrene] (PSDIB) was prepared as an oxidant by iodination and acylation of polystyrene. A task-special inonic liquid, TEMPO-IL was prepared through immobilization of 2,2,6,6-tetramethyl-piperidin-4-ol-N-oxyl to inonic liquid by the literature method. A series of primary and secondary alcohols were successfully oxidized to the corresponding aldehydes and ketones in good yields, respectively, with poly[4-(diacetoxyiodo)styrene] (PSDIB) in the presence of TEMPO-IL (cat.) in [bmim][BF4] at room temperature. This system is environment-friendly and economic in which all the oxidant, catalyst and the solvent can be recovered and reused.We also studied the oxidation of alcohols to methyl eaters using PhIO in the presence of KBr in mixed solvent of methanol and 0.5 mol-L^-1 HBr solution (2:1). Benzyl alcohol can be transformed to benzoate in 90% yield with 3.5 equiv. of PhIO and 1.0 equiv. of KBr in the mixed solvent at room temperature for 6 hours. It is found that under these conditions benzyl alcohols with electron withdrawing groups in para position can be oxidized to the corresponding methyl esters.