Research On The Selective Reduction Of Nitro Aromatics In Fe-CO₂-H₂O System

Anilines are important intermediates and crude materials in organic synthesis, andwidely used in pharmaceuticals, agricultural chemicals, dye etc. Preparation of anilines fromthe reduction of the corresponding nitro aromatics is the main method.In this paper, the Fe-CO₂-H₂O system was explored for selective reducep-chloronitrobenzene (p-CNB)and m-dinitrobenzene to p-chloroaniline and m-nitroanilinerespectively. The carbonic acid formed by carbon dioxide and water can promote thereduction. The effects of different reaction parameters, such as temperature, CO₂ pressure, theratio of raw materials on the reaction conversion and selectivities are investigatedsystematically. The optimized conditions of p-chloronitrobenzene and m-dinitrobenzene wereestablished as follows:For the reduction of p-CNB, the reactions were carried out in a 100mL Parr autoclaveand the optimized conditions were: n(p-CNB)=10mmol, n(Fe)/n(p-CNB)=3, T=120℃,P(CO₂)=7.0 MPa, t=8h, V(water)=35mL, stirring rate 480rpm. the yield of p-chloroaniline isabove 99%;For the reduction of m-dinitrobenzene, the reactions were carried out in a 75mL stainlesssteel autoclave and the optimized conditions were: n(m-DNB)=2.5mmol, n(Fe)/n(m-DNB)=3,T=60℃, t=3h, P(CO₂)=3.4MPa, V(total)=12.5mL, V(H₂O)/V(C₂H₅OH)=8:1, theconversion of m-dinitrobenzene was up to 100% and selectivity toward m-nitroaniline almostreached 100%.This method is characterized by high reaction conversion as well as high selectivitytoward product. After the reduction, the separation of the aniline can be carried withoutaddition of base. Theoretically carbon dioxide, water and unreacted iron powder in thereaction system can all be reused and there is no waste water discharge and hence the problemof the waste water pollution to environment is avoided.