| Selective oxidation of alcohols into aldehydes and ketone compounds is an important chemical reaction in organic synthesis.Traditional oxidation methods mostly use oxidants such as potassium dichromate,chromium oxide,potassium permanganate,sodium hypochlorite,etc.,and the reaction produces a large amount of metal salt waste,which is not the development concept of today's green chemistry.The green oxidation reaction of O2 as an oxidant is the essence of organic synthesis.O2 has a wide range of sources,low prices,and does not cause environmental pollution.Therefore,O2 as an oxidant is an inevitable trend for the development of green oxidation reactions.In organic synthesis,2,2,6,6-tetramethylpiperidine-nitrogen radical?TEMPO?is often used as a catalyst for alcohol oxidation.TEMPO has the functions of capturing free radicals,quenching singlet oxygen,and selective oxidation.The TEMPO oxidation system has the advantages of mild reaction conditions and high selectivity.However,the traditional TEMPO catalytic system mostly uses NaClO as the oxidant,and the halide?such as Br—?or transition metal?such as Ru,Pd,Cu?compounds are used as co-catalysts.Large amounts of saline wastewater are difficult to handle.In the research of the production of nylon 11 monomer 11-aminoundecanoic acid from hydrogenated castor oil made from renewable resources,our laboratory uses TEMPO/NaClO oxidation system to prepare 12-Methyl carbonyl stearate by oxidation.12-Methyl carbonyl stearate has achieved high conversion and yield,but the use of NaClO as an oxidant in the oxidation system has environmental protection problems,so it is necessary to develop a more environmentally friendly and applicable oxidation route.In view of the above problems,an ionic liquid-supported TEMPO catalyst and an acidic ionic liquid co-catalyst were prepared in this experiment.The selective oxidation of methyl 12-hydroxystearate and other alcohols was studied with O2 as the oxidant.It is a green and efficient method for the catalytic oxidation of long-chain fatty alcohols.The main research contents and results of this thesis are as follows:?1?Preparation and Characterization of Ionic Liquid CatalystsChloroacetic acid,4-OH-TEMPO and N-methylimidazole were reacted at room temperature and pressure for 12 hours to prepare TEMPO-loaded ionic liquid?IL-TEMPO-Cl?,followed by a precipitation reaction with AgNO2 to convert anions into NO2—,an ionic liquid-supported TEMPO catalyst?IL-TEMPO-NO2?was prepared,achieved the combination of TEMPO and NO2—,the yield was 95%.It was characterized by infrared spectrum,ultraviolet absorption spectrum and high resolution mass spectrometry.?2?Preparation and purification of 12-hydroxystearateThe hydrogenated castor oil was transesterified with methanol,and 0.3mol%NaOH was used as a catalyst,and reacted at 70°C for 1.5 hours to obtain methyl 12-hydroxystearate.The purity was about 85%.The n-heptane was recrystallized to remove Impurities such as stearic acid were used to obtain 99%methyl 12-hydroxystearate as an oxidation reaction substrate.?3?Catalytic oxidation of methyl 12-hydroxystearateUsing methyl 12-hydroxystearate as a substrate,IL-TEMPO-NO2 as a catalyst,and O2 as an oxidant,the synergistic catalytic oxidation effect of IL-TEMPO-NO2 and different types of acidic ionic liquids was investigated.The results show that IL-TEMPO-NO2 and[PyS][OTf]have the best synergistic catalytic effect.We investigated the effects of catalyst amount,solvent and reaction time on the oxidation of methyl 12-hydroxystearate,and the optimal reaction conditions were determined:the amount of catalyst IL-TEMPO-NO2 and co-catalyst[PyS][OTf]were 30 mol%of the oxidized substrate,respectively,respectively.Ethyl acetate was used as a solvent.The reaction was carried out at room temperature for 12 hours.The yield of methyl 12-carbonylstearate reached 93%.?4?Ionic liquid catalyzes the oxidation of various alcoholsThe catalytic oxidation system of IL-TEMPO-NO2/[PyS][OTf]with O2 as oxidant was used to oxidize multiple primary alcohols,secondary alcohols and long-chain fatty alcohols.The results showed that:the primary aromatic alcohols and secondary alcohols had the best oxidation effect,and the conversion and selectivity could reach 99%;the oxidation of long-chain fatty alcohols also had a good catalytic effect,and the yield reached more than90%;The catalytic oxidation effect of naphthenic alcohol is not good,and the highest oxidation yield is 56%.?5?Analysis of oxidation reaction mechanismThe mechanism of catalytic oxidation reaction was explored through controlled variable experiments.It is speculated that the possible reaction mechanism is:IL-TEMPO-NO2 ionized NO2—oxidizes TEMPOH into nitrogen carbonyl cations with strong oxidizing properties under acidic conditions,which is reduced to NO by itself.O2 as an oxidant oxidizes NO to NO2,the nitrogen carbonyl cation oxidizes the alcohol to the corresponding aldehyde or ketone,and is itself reduced to TEMPOH to participate in the oxidation reaction again.The co-catalyst[PyS][OTf]provides an acidic environment for the catalytic system. |
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