Study On Nitration Of 2,4-Dichlorotrifluorotoluene Catalyzed By Ionic Liquids

The nitro derivatives of trifluoromethyl are a kind of chemical products widely used in the fields of medicine,agricultural medicine and dyestuff.The nitration product of 2,4-dichlorotrifluoromethyl is a typical representative of trifluoromethyl derivatives,and the development of nitration process is of great significance.At present,there are many shortcomings in the widely used nitration process of nitric acid sulfuric acid mixed acid,such as 1.The nitration efficiency of the mixed acid process is affected by the concentration of the mixed acid,and the mixed acid can not be used repeatedly.2.A large amout of waste acid will be produced in the nitrification process,which will cause environmental pollution and post-treatment problems.3.Mixed acid will cause corrosion to reaction equipment.Ionic liquids,as green catalysts and solvents,have made progress in many organic reactions,but in the past research,the research on the nitration of aromatic compounds such as trifluoromethyl,which are replaced by strong electron absorbing group,is relatively rare.In this paper,2,4-dichlorotrifluoromethyl was used as nitrifying substrate,nitric acid as nitrifying agent,and a variety of ionic liquids with strong acidity as nitration catalysts.In order to explore the feasibility of nitration of2,4-dichlorotrifluoromethyltoluene catalyzed by ionic liquids,12 kinds of ionic liquids based on triethylamine,N-methylpyrrolidone and N-methylimidazole as cation skeleton were synthesized by"one-step"method,and the ionic liquids were characterized by providing anions with trifluoromethylsulfonic acid,sulfuric acid,trifluoroacetic acid and p-toluenesulfonic acid.Using 4-nitroaniline as indicator,the relative acidity of each group of ionic liquids were compared by UV Vis combined with Hammett indicator.The order of acidity of each group of ionic liquids is:trifluoromethylsulfonic ionic liquids>hydrogen sulfate ionic liquids>p-toluenesulfonic ionic liquid>trifluoroacetic ionic liquids,which is consistent with the acidity of conjugated acid.The acidity of the synthesized ionic liquids were confirmed to be Br?nsted acid by IR pyridine probe.In order to further enhance the acidity of ionic liquids,triethylamine and N-methylimidazole were used as cation skeletons,and sulfonic acid functional groups were introduced through quaternization reaction.Four functional ionic liquids were synthesized and characterized,including[TEA-PS][OTf],[TEA-PS][HSO₄],[Hmim-PS][OTF],[Hmim-PS][HSO₄],the combination of UV-vis and Hammett indicator to test acidity shows that it is indeed strengthened.The synthesized ionic liquids were used in Nitration of 2,4-dichloro-trifluoromethyl.It was found that 12 kinds of ionic liquids directly synthesized by one-step method can make the reaction obtain nitration products,but the conversion rates were relatively low.Under the catalysis of[TEA][OTf],the amount of catalyst is25%of the substrate,the conversion rate is 50.6%at 80?,and the reaction lasts for2 hours.The reaction conditions such as catalyst dosage,reaction temperature,reaction time and nitric acid dosage were optimized,and after 5 cycles,the catalytic effect was only slightly reduced.Four sulfonic acid functionalized ionic liquids were used in Nitration of2,4-dichlorotrifluoromethyl.The results show that sulfonic acid functionalization is an effective method to improve the catalytic activity of ionic liquids.At 80?,nitric acid reacts with 2,4-dichlorotrifluoromethyl in a molar ratio of 3:1,and 35%and 25%of the molar amount of substrate[TEA-PS][OTf]and[Hmim-PS][OTf]are added as catalysts respectively,and the conversion can reach 89.1%and 77.2%respectively,and the activity of the catalyst has not decreased after 5 cycles.In this paper,the rare earth metal salt was dissolved into the ionic liquid to make the rare earth metal composite ionic liquid,and the reaction conditions were explored.Ytterbium trifluoride sulfonate has higher catalytic activity when added into ionic liquid.Under the catalysis of Yb?OTf?3 rare earth metal sulfonate and rare earth metal composite ionic liquid obtained from sulfonic acid functional ionic liquid[TEA-PS][OTf],at 80?,the reaction can be completed in about 2 h.The optimum amount of rare earth metal composite ionic liquid is 15%of the molar amount of nitration substrate 2,4-dichlorotrifluoromethane,and the molar ratio of rare earth metal salt to ionic liquid is 1:2.Under the above conditions,the conversion rate of nitrification can reach 92.5%.