Research On The Application Of Biomass-based Sliver Nanoparticles In The Transformation Of Terminal Alkynes

Under the background of"dual carbon"strategy,as the only renewable carbon resource,the exploitation and utilization of biomass has become one of the most attractive action plans.In addition to the production of high value-added fuels and chemicals,biomass is also used to synthesize a variety of functional materials,such as bio-based polymers,bio-based plastics,bio-based fibers,etc.Among them,the biomass-derived activated carbon,with good porosity,thermal stability,surface function and chemical reactivity,is an ideal catalyst support material.Highly active carbon-loaded metal catalysts could be synthesized by loading metal nanoparticles on biochar,which have been successfully used in experimental research and industrial production,and with excellent catalytic effects.On the other hand,the transformation of terminal alkynes is one of the important reactions in organic synthesis,which showed great potential in the production of fine chemicals,such as olefins,ketones,imines.However,most of the catalytic systems for terminal alkynes are homogeneous systems,there still exist some problems such as difficult catalyst/product separation,relatively harsh reaction conditions and difficult catalyst recycling.Therefore,it is necessary to develop efficient,green catalytic systems for the conversion of terminal alkynes.Based on this,a series of biomass-based carbon-loaded silver catalysts（Ag@C）were synthesized and applied to catalyze the halogenation and cleavage reaction of terminal alkynes,the haloalkynes and nitrile compounds was obtained,respectively.The composition,morphology,valence and physicochemical properties of the catalyst were investigated through structural characterization.Through the research on catalyst screening,reaction condition optimization,mechanism research and catalyst recycling,a new method for efficient catalytic conversion of terminal alkynes has been established.The specific research content is as follows:Firstly,in this paper,using bamboo powder as raw material and Ag NO₃ as metal precursor,three Ag@C catalysts（Ag@C-1,Ag@C-2,Ag@C-3）with different Ag loading（6.2%,12.1%,15.5%）were prepared by an in-situ reduction-pyrolysis process.The XRD and XPS results indicated that the catalyst was mainly composed of metallic silver nanoparticles Ag（0）.SEM and TEM characterization results showed that the Ag nanoparticles with average size of 11.8～16.5nm were uniformly dispersed on the mesoporous carbon.The average pore size increased as the Ag loading increased,together with a decreasing in the total pore volume.Secondly,we used the above catalysts for the halogenation reaction of terminal alkynes and N-halosuccinimides（NXS,X=Cl,Br,I）to produce haloalkynes.Used phenylacetylene and N-chlorosuccinimide（NCS）as model substrates,investigated the effects of catalyst types,base,reaction solvent,reaction time and reaction temperature on the reaction activity.Used Ag@C-2as the best catalyst,Me CN as the solvent and KOAc as the base,93%yield of 1-chlorinated alkynes was obtained after 6 h at room temperature.The catalytic system was further extended to iodination,and bromination reactions of the terminal alkyne,with high catalytic efficiency and good compatibility of substrates.In addition,the Ag@C-2 catalyst could be recycled three times without obvious deactivation.Competitive experiments and theoretical calculations showed that the base could effectively activate chlorinated reagents NCS and reduced the N-Cl bond energy,thus achieved efficient conversion at room temperature.Finally,the method was applied to the synthesize the important organic intermediates o-dihalogenated heteroalkenes and N-containing organic compounds ynamine from terminal alkynes.Finally,Ag@C catalyzed C≡C bond cleavage of terminal alkyne to nitrile was also studied.We used phenylacetylene and azidotrimethylsilane（TMSN3）as model substrates,and optimized the reaction parameters such as catalyst type,catalyst amount,reaction solvent,reaction time,and reaction temperature.Used Ag@C-2 as the best catalyst,DMSO as the solvent,87%yield of benzonitril was obtained after 12 h at 100 ^oC.The catalytic system was used for the conversion of various terminal alkynes with different substituents,and good yields were achieved.Finally,the Ag@C-2 catalyst had good stability,the yield remained almost unchanged after four consecutive runs.