Green Catalytic Synthesis Of Cyclohexanone Oxime And Nitrocyclohexane

Direct C-H functionalization of inactive alkanes is an important strategy to streamline the preparation of new compounds,which enable access to higher-value chemical products and the increase of the efficiency of hydrocarbon conversion from petroleum.Cyclohexanone oxime is an important chemical intermediate in petrochemical industries for the manufacture of nylon-66.Cyclohexanone oxime is currently produced from cyclohexane and ammonia in multiple steps in most traditional processes which involve technical bottlenecks in the oxidation of cyclohexane to intermediate cyclohexanone.Therefore,the important goals of developing green chemistry today are to improve the effective utilization of existing reaction materials and resources and to seek new reaction processes.Direct synthesis of cyclohexanone oxime from cyclohexane and ammonia is economic,green and sustainable,but design of high-performance catalyst is the key technology of the whole route.The synthesis of cyclohexanone oxime by hydrogenation of nitrocyclohexane is also an effective way to improve the utilization of resources.However,the nitration of C-H bond in cyclohexane is difficult.The current nitrification processes have issues such as pollution of the environment by nitrating agents and C-C skeleton cleavage at high temperature.By designing new multifunctional composite catalyst and selecting suitable and clean nitrating agent,new processes to prepare cyclohexanone oxime and its intermediate nitrocyclohexane from cyclohexane in one step were explored in this paper.This realized the efficient and green synthesis of cyclohexanone oxime.The main research contents include:?1?Transition metal modified hollow-structured titanium-silicalite?M/HTS?were designed and prepared.And a new process for the direct synthesis of cyclohexanone oxime from cyclohexane with M/HTS as catalyst,H₂O₂ as green oxygen source,ammonium acetate or ammonia as nitrogen source in CH₃CN-CH₃COOH cosolvent was studied.By optimization of reaction conditons,Ni/HTS gave a cyclohexanone oxime selectivity of 51%at a cyclohexane conversion of 13.6%.Based on catalytic experiment results,catalyst characterization,DFT calculations and in-situ FT-IR tracking reaction process,a reaction mechanism was proposed.The tetrahedral TiO₄ species in Ni/HTS was identified as the bifunctional active center of the catalytic reaction.Ni metal points can effectively regulate TiO₄ to catalyze the selective oxidation of cyclohexane C-H bond to cyclohexanone,followed by oximization with hydroxylamine generated in situ from ammonium acetate activated by TiO₄ simultaneously,to cyclohexanone oxime.And the results were confirmed by the reaction occurring by tandem catalysis.?2?An operationally simple,green and effective alkane C-H nitration method was studied to access nitroalkanes without cleavage of the C-C skeleton.The different metal nitrates as nitrating agents were explored in cyclohexane nitration reaction as a probe reaction.It was found that Fe?NO₃?₃·9H₂O,Cr?NO₃?₃·9H₂O and Bi?NO₃?₃·5H₂O were the most effective nitrating agents.By optimization of reaction conditons,the conversion of cyclohexane 53.7%and nitrocyclohexane selectivity of 92.1%were achieved with Fe?NO₃?₃·9H₂O and trifluorotoluene as nitrating agent and solvent respectively at 145 ^oC.This kind of metal salt catalyst is suitable for a wide range of substrates,and preferentially nitrates cycloalkyl when the substrate contains both cycloalkyl group and aryl groups.The catalytic experiments of metal oxides and theoretical modeling of quantum chemistry have shown the iron oxide decomposed in situ as a key catalytic species for the alkane C-H and NO₂ activation.Nontoxic and inexpensive Fe?NO₃?₃·9H₂O plays a dual role as catalyst precursors as well as nitro sources for the transformation.The preliminary mechanistic studies of the reaction suggested that the reaction is radical reaction mechanism,and that hydrogen atom abstraction is the rate-limiting step of the nitration.