Preparation Of 4-nitro-o-xylene From Liquid Phase Catalytic Nitration Of O-xylene With Nitrogen Dioxide

4-Nitro-o-xylene is mainly used in the production of the newherbicide N-mevalin,vitamin B₂ and dimethylaniline.At present,the industrial synthesis of 4-nitro-o-xylene is mainly obtained from the nitration of o-xylene with nitro-sulfur mixed acid.But the nitration product in this process is mainly 3-nitro o-xylene.Only a bit of 4-nitro o-xylene is produced.And the large amount of waste acid discharged pollutes the environment.In this paper,a new solid acid catalyst is designed and prepared to replace the existing liquid acid.Replace nitric acid with nitrogen dioxide（NO₂）as a green nitrifying agent.A new process route for preparing 4-nitro-o-xylene withhigh selectivity under mild conditions in oxygen with o-xylene as raw material.Various nitration methodshave been explored to nitrate o-xylene,and it is found that oxygen has a significant promotion effect on the nitrification capacity of NO₂.the catalytic effects of different Br（?）nsted acids were compared,and the results showed that silicic acid,as a new type of solid super acid,has stable and excellent catalytic performance and is easy to separate from the product.Under optimized reaction conditions,the conversion rate of o-xylene is 46.7%,the selectivity of 4-nitro-o-xylene is up to 64.6%,and the ratio to o-xylene is 1.94.A series of microstructure characterizations such as N₂ adsorption,XRD,FT-IR,TG/DTG,NH₃-TPD,Py-FT-IR,etc.were carried out on silicon sulfonic acid,and the mechanism of its catalytic nitration reaction was speculated.In order to further improve the selectivity of 4-nitro o-xylene,the catalytic performance of different Lewis acids was investigated,and it was found that under the catalysis of BiCl₃,the selectivity of 4-nitro-o-xylene can be significantly improved.however,BiCl₃ is easilyhydrolyzed in the nitration reaction andhas poor stability.therefore,the chemical bonding method is used to bond BiCl₃ to thehydroxyl-rich silicic acid surface to prepare a solid-supported BiCl₃-H₂SiO₃catalyst.Under optimized reaction conditions,the conversion rate of o-xylene is 52.4%,the selectivity of 4-nitro o-xylene can reach 68.4%,and the ratio of o-xylene is2.43.And the solid-supported Lewis acid catalyst maintains good stability in this reaction.And a series of characterization of BiCl₃-H₂SiO₃,such as XPS,N₂ adsorption,XRD,FT-IR,TG/DTG,NH₃-TPD,Py-FT-IR,etc.,Combined with the experimental data and characterization results under the system the reaction mechanism was explored.In this paper,a mild,green andhigh-efficiency liquid phase catalytic nitrification method has been developed.the introduction of molecular oxygen significantly improves the nitration efficiency,and the solid acid catalyst further improves the selectivity of the target product,and is easy to separate and reusable.From the theoretical point of view of Br（?）nsted acid and Lewis acid catalysis,it was discovered that two different solid acid catalysts can improve their reaction activity and target product selectivity,further improve the atom utilization rate,and have potential industrial application value.