| The selective oxidation of alcohols to the corresponding aldehydes or ketones compounds is of great importance in both organic synthesis experiments and industrial production,but the oxidation conditions are often rather harsh and It may produce a lot of organic wastes.2,2,6,6-tetramethylpiperidine-nitroxide(TEMPO)is a mild and efficient catalyst,but it is a challenge to recovery the expensive TEMPO catalyst in homogeneous catalytic systems.Therefore,this paper focuses on the construction of heterogeneous catalytic system by chemical immobilization of 4-hydroxy-2,2,6,6-tetramethylpiperidine-nitroxide(4-OH-TEMPO)with activated carbon,graphene oxide or ionic liquid as a carrier material.The catalytic system is intended to achieve the selective oxidation of alcohols under the conditions of room temperature,atmospheric pressure.At the same time,it can reduce the difficulty of post-processing and achieve the recycling use of the catalyst system.Firstly,activated carbon which has excellent adsorption properties was used as the carrier material in this paper,the oxygen-containing functional groups were produced on the inner and outer surfaces of the activated carbon by acidification treatment.The carboxyl groups on the surface of activated carbon reacted with 4-OH-TEMPO,synthesising the AC-TEMPO catalyst.Then,considering the excellent adsorption of activated carbon,the activated carbon-TEMPO /NOx catalytic system was constructed by adsorbing NOx to channels of activated carbon.This catalysts syetem were characterized by IR,elemental analysis,thermogravimetric analysis,laser fiber Raman,electron spectroscopy and electron paramagnetic resonance.The loading of 4-OH-TEMPO reached to 1.011 mmol / g.In the oxidation of 17 common alcohols,the catalytic system can achieve 99% efficiency of most aromatic alcohols within 3 h.Meanwhile,the post-treatment is much more simple and easy to operate.With another 10 cycles of benzyl alcohol oxidation,the recovered catalyst can also afford above 88% efficiency.Secondly,the graphene oxide(GO)which was treated by modified Hummers method was used as another carrier material.After 4-OH-TEMPO was immobilized on the surface of graphene oxide by acylation,the GO-TEMPO was synthesised.two-component catalytic oxidation system,GO-TEMPO/TBN was constructed with TBN as a nitrogen source.The optimal oxidation conditions were determined for the catalytic system: 0.2 g GO-TEMPO catalyst,20 mol% TBN,0.1 g deionized water were added to 1 mmol of benzyl alcohol substrate,dissolved in 8 ml of acetonitrile solvent.Under the optimum conditions,14 kinds of common alcohol substrates were oxidized by the catalytic system,and most aromatic alcohols were selectively oxidized to aldehydes and ketoneswith over 99% selectivity.Finally,4-OH-TEMPO was reacted with N-methylimidazole by chloroacetyl chloride to obtain TEMPO type ionic liquid.The anion was converted into or through precipitation.reaction to realize the organic combination of TEMPO and nitrogen source.It is the first time to synthesis the functionalized ionic liquid type one-component catalyst,which achieve the organic combination of TEMPO and nitrogen source.The ionic liquid type catalysts were characterized by nuclear magnetic spectroscopy,infrared spectroscopy and high precision mass spectrometry.The reaction process and product were analyzed by GC and GC-MS.The catalyst can achieve over 99% oxidation of benzyl alcohol at room temperature usuing air as oxidant in 3 h.After the oxidation reaction,the oxidation products and the ionic liquid type catalyst can be separated by liquid separation.After five cycles of oxidation reaction,the the recovered catalyst system still maintains the high efficiency oxidation ability and the catalyst recovery rate isas high as 95%. |
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