Study On Selective Oxidations Of Alcohols

Intermediates of alcohols are widely used in the synthesis of dyes,spices,drugs,and other fields.Therefore,as an important research topic,the selective oxidation of alcohols has received much attention.Conventional methods to oxidize alcohols often involve heavy metal oxidants,such as dichromate,potassium permanganate and manganese dioxide,etc.The cost is high and the use of organic solvants will do harm to the environment.Hence,study on green catalytic systems for the oxidation of alcohols with high efficiency is still a hot spot.Researchers aim to improve the selectivity of the target product,reduce or even eliminate the environmental pollution caused by the reaction,that is,to achieve green oxidation.In this work,several novel,green catalytic systems were developed and applied for selective oxidation of alcohols with O₂ or H₂O₂ as green oxidants.A catalytic system composed of 1,1-diphenyl-2-picrylhydrazyl radical?DPPH?and tungsten oxide/alumina?WO3/Al2O3?was developed and employed in the oxidation of primary and secondary alcohols.The catalytic system has obvious color changes in the reaction process,making it easy to detect the reaction.The conversion of alcohols and selectivity for aldehydes are higher than other radical-based catalytic systems.Take the oxidation of benzyl alcohol for instance,its conversion could be up to 65%and the selectivity of benzyl aldehyde could turn to 95%after 4 hours.In addition,a plausible catalytic pathway was proposed.Catalyst Cu?0?/Cr₂O₃ was synthesized and used in the dehydrogenation of primary and secondary alcohols.Synthesis of Cu?0?/Cr₂O₃ was based on copper-chromium hydrotalcite?Cu-CrHT?with a simple calcination method.The catalyst can catalyze the substrate to dehydrogenate,thus obtaining the corresponding aldehydes and ketones with great efficiency.For example,in the oxidation of benzyl alcohol,the conversion reached 99%and the selectivity for benzyl aldehyde could be 99%after 4 hours.When the reaction was completed,the catalyst could be quickly recovered by centrifugation and reused for at least five recycles without obvious loose of copper nanoparticles.A novel homogeneous catalyst RuNP-xC-yN was synthsized and employed in the aerobic oxidation of 5-?Hydroxymethyl?furfural?HMF?.The catalyst has an obvious core-shell structure and was divided into three layers.The outer one was connected to?Me0?3SiCH₂CH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂,which made the catalyst lipophilic III and the whole reaction system homogeneous.The reaction was carried out under atmospheric pressure.After 4h,the conversion of HMF reached 94%and the selectivity of 2,5-diformylfuran?DFF?was up to 89%.The solvent is a key factor affecting the reaction efficiency.When methyl isobutyl ketone?MIBK?acted as the solvent,the reaction afforded the highest conversion and selectivity.The PdNP-xC-yN phase transfer catalyst was synthesized by improving the RuNP-xC-yN catalyst system.By adjusting the solution pH,PdNP-xC-yN can freely transfer between the ether and aqueous phases.Compared to the RuNP-xC-yN catalytic system,PdNP-xC-yN catalytic system can avoid the radioactivity of Ru and the greater toxicity of methyl isobutyl ketone with expanded substrate scope.Most of all,the catalytic system offered an innovative method of catalyst recovery without filtration or centrifugation.At the time of recovery,pH of the solution was adjusted to acidic,thus the catalyst entered the aqueous phase.Then decanted the organic phase and analyzed its composition.After the analysis is complete,fresh organic phase was added and another run could be started.Au was loaded adopting the deposition precipitation method on MnO₂ as the support to afford Au/MnO₂ catalyst.In order to explore how different structures of MnO₂ would affect the catalytic performance,several kinds of the MnO₂ nano-structures were synthesized.And the resulted catalysts were used in the oxidation of 5-?hydroxymethyl?furfural in the presence of O₂.Au/MnO₂ system was also compared with other Au supported catalytic systems.At atmospheric pressure,the conversion of HMF could achieve 82%,and the selectivity of DFF was 99%.Au-Pd/MnO₂ catalytic system was synthesized by improving Au/MnO₂ catalytic system.Au-Pd nanoparticles were synthesized by a mild biological approach with a uniform particle size and well dispersion in the solution.EDS and XPS spectra demonstrate Au and Pd formed alloys instead of simple physical mixture of Au nanoparticles and Pd nanoparticles.And the synergistic effect of Au and Pd avoided Au nanoparticles from deactivation by the intermediate?such as carboxylic acid?.The solvent was also changed from DMF to water,but the yield didn't significantly decrease.Under normal pressure,the conversion of HMF reached 76%,and the selectivity of DFF reached 98%.The iron hydrogen phosphate crystal?FeHPO?with mimic peroxidase activity was designed for the selective oxidation of benzyl alcohol.FeHPO is capable of catalyzing hydrogen peroxide to generate hydroxyl radicals,thus affording the oxidation of benzyl alcohol to benzyl aldehyde.Besides,pH,temperature and thermal time all have great influence on the oxidation.