The Separation And Characterization Of O-xylene Nitration By-products

3-nitro-o-xylene and 4-nitro-o-xylene as two kinds of nitro-o-xylene isomer are important organic intermediates,are widely used in the dyes,medicines,plastics,rubber additives,sterilization and plant growth regulators.The industrial nitrification of o-xylene adopts a nitric-sulfur mixed acid process,which produces a large amount of waste acid and seriously pollutes the environment.Therefore,this paper carried out the separation and characterization of nitro-o-xylene by-products,and explored the formation mechanism of by-products,providing guidance for further improving the synthesis process,controlling the nitrification process,reducing costs,reducing three wastes,and achieving continuous and stable production.In this paper,the main product 4-nitro-o-xylene and five by-products were separated by silica gel column chromatography and recrystallization,2,3-dimethyl-1,4-dinitrobenzene,1,2-dimethyl-3,5-dinitrobenzene,1,2-dimethyl-3,4-dinitrobenzene,3,4-dimethyl-2,6-dinitrophenol and 2,6-dimethyl-3,5-dinitro-2,5-diene-1,4-cyclohexanedione.The structure was characterized by Fourier transform infrared?FTIR?spectroscopy.A high performance liquid chromatography method for the determination of nitrification products,by-products and raw materials was established,and the internal standard method was used for quantitative analysis.The optimal chromatography conditions were obtained:nitrobenzene was used as the internal standard,Hypersil ODS2 column?250 mm×4.6 mm,5?m?,UV detection wavelength was 211 nm,mobile phase methanol/0.1%phosphoric acid water=60/40?V/V?,The flow rate was 0.8 mL·min^-1,the column temperature was 25?,and the injection volume was 20?L.According to the established internal standard method,the influence of various factors on the by-products during the nitrification reaction was discussed.The amount of by-product1,2-dimethyl-3,5-dinitrobenzene increased with the increase of the ratio,the selectivity was the highest when the ratio was 1:1.1,and the amount of total by-products was the least.The amount of by-product 1,2-dimethyl-3,5-dinitrobenzene increases as the reaction time increases,the selectivity is highest at a time of 0.5 h,and the amount of total by-products is the least.The amount of by-product 1,2-dimethyl-3,5-dinitrobenzene decreases first and then increases with increasing temperature,the selectivity is highest at 20?,and the amount of total by-products is the least.