Study On Catalytic Oxidation Of Alcohols By Piperidine-1-oxyl Task-special Ionic Liquids

Ionic liquids are liquid salts at room temperature which are composed of anions and cations. Oxidations of alcohols are catalyzed by the method based on piperidine- -1-oxyl and ionic liquids, which not only make catalysts reusably, but also have important meaning and application for the green chemical engineering.In this paper, the auther disclosed a catalytic system, 4-hydroxy- -2,2,6,6-tetramethylpiperidine-l-oxyl(TMHPO)+ CuCl, which was used to substitute the existent one, expensive 2,2,6,6-tetramethylpiperidine -l-oxyl(TEMPO)+ CuCl, for the oxidation of benzylic alcohols. For optimizing the reaction condition, the influence of several factors on reaction was studied, and then a satisfied reaction condition was obtained in 24 hours at 60℃with 2 mmol benzylic alcohols, 1MPa O2, 5 mol% TMHPO, 3 mol% CuCl and 1 mL [bmim]PF6. In this condition, the conversion of benzylic alcohol was 71%, the selectivity of benzaldehyde were 97%, but the catalytic system couldn't be recycled. Then the oxidation of series of aliphatic and aromatic alcohols were invested in the same condition, and they illustrated that this catalytic system had the best effect in aromatic primary alcohols .Basing on TMHPO, four types of piperidine-1-oxyl task-special ionic liquids with imidazole ionic liquid tags were synthesized (of these, TSIL-Ⅰand TSIL-Ⅱwere synthesized of the first). The molecular structures of TSIL-Ⅰand TSIL-Ⅱwere confirmed by FT-IR, EA and NMR, etc. Then, using benzylic alcohol as substrate, oxygen as oxidant, TSIL-Ⅰas catalyst, the auther studied the influence of several factors on reaction, and confirmed a appropriate condition: 2 mmol benzylic alcohols, 3MPa O2, 5 mol% TSIL-Ⅰ, 3mol%CuCl, 1ml H2O, room temperature for 24 hours. In this condition, the conversion of benzylic alcohol was 91%, the selectivity of benzaldehyde were 98%, but the catalytic system couldn't be recycled. Also, the oxidation of 1-penylpropan-1-ol were invested in the same condition, and it indicated that catalyst was better in aromatic primary alcohols .By seeing about the influencing factors, a satisfied condition of the oxidation system, benzylic alcohol, NaClO and TSIL-Ⅱ, was obtained: 2 mmol benzylic alcohols, 6mmol NaClO, 5 mol% TSIL-Ⅱ, room temperature for 60 minutes. In this condition, almost all the benzylic alcohol was oxidated to benzaldehyde, and TSIL-Ⅱ can be recycled and reused for five runs without any significant loss of catalytic activity.