Research On The Synthesis Of 3,5-Dichloroaniline

As an important organic intermediate,3,5-dichloroaniline can be used for the synthesis of dyes,pesticides and pharmaceuticals.In recent years,more and more attention has been given to the exploitation and utilization of 3,5-dichloroaniline.The synthesis of 3,5-dichloroaniline from 4-nitroaniline by chlorination,diazotization-dediazoniation and reduction is unsatisfactory with low chlorine utilization rate,high treatment cost of by-product sodium sulfate and low yield.In order to solve these problems,we provide some improvement methods in our article.Firstly,2,6-dichloro-4-nitroaniline was prepared from 4-nitroaniline by Cl2-HCl/H2O2 alternating chlorination.In the first phase of chlorination,4-nitroaniline was chloridized by Cl2 which was introduced into the reaction vessel at the rate of 80 ml/min at 70?,using 15%hydrochloric acid as the solvent.The molar ratio of Cl2/4-nitroaniline was 2.15.The product was got by filtration after the reaction finished,detected by TLC.In the second phase of chlorination,after the supplement of 4-nitroaniline,30%hydrogen peroxide solution was used to chlorideze the 4-nitroaniline at 55? for 1.5h.The molar ratio of H2O2/4-nitroaniline was 2.2.The product was got by filtration after the reaction finished.The leachate in which the concentration of hydrogen chloride was closed to 15%could be reused,so very few wasterwater was discharged.The percent conversion of 4-nitroaniline was 100%.The yield of 2,6-dichloro-4-nitroaniline was 94.4%.The structure of product was confirmed by 1H-NMR and 13C-NMR.Secondly,3,5-dichloronitrobenzene was prepared from 2,6-dichloro-4-nitroaniline by diazotization-dediazoniation,using 98%H2SO4 and 2.2mol/L ammonium nitrite solution as diazotization agent.The optimal conditions for reaction was as follows:n(2,6-dichloro-4-nitroaniline):n(NH4NO2):n(H2SO4)=1:1.1:2.5,reaction temperature was 55?,reaction time was 2h,ethanol displayed as solvent and reducting agent.After neutralization by ammonia water and filtration,the product was got.The ethanol in leachate was recycled to reuse and ammonium sulfate was sold as raw material of nitrogenous fertilizer.The percent conversion of 2,6-dichloro-4-nitroaniline was 100%.The yield of 3,5-dichloronitrobenzene was 89.5%.The structure of product was confirmed by GC-MS,1H-NMR and 13C-NMRFinally,3,5-dichloroaniline was prepared by two methods:catalytic transfer hydrogenation reduction and catalytic hydrogenation reduction.In the catalytic transfer hydrogenation reduction,the optimal conditions for reaction was as follows:n(3,5-dichloronitrobenzene):n(formic acid)=1:3.6,reaction temperature=30?,reaction time=3h,ethanol as solvent,Na2CO3 as aided reducing agent(4 wt%),Pd/C as catalyst(5 wt%).The yield of 3,5-dichloroaniline was 93.8%.The structure of product was confirmed by GC-MS,1H-NMR and 13C-NMR.In the catalytic hydrogenation reduction,3,5-dichloroaniline was synthesized by 3,5-dichloronitrobenzene and H2 in a sealed autoclave.The optimal conditions for reaction was as follows:reaction temperature=50?)reaction pressure=1.6MPa,ethanol as solvent,Raney Ni as catalyst(4 wt%).The yield of 3,5-dichloroaniline was 90.1%.Through comparison and analysis,the method of catalytic hydrogenation reduction was more suitable for industry production because of the low cost,although the method of catalytic transfer hydrogenation reduction had the advangages of simplicity,mild reaction conditions,no dechlorination reaction.