Catalytic Transfer Hydrogenation Of Nitroarenes Under Different Catalytic Systems

The conversion of aromatic nitroarenes to the corresponding amines and N-arylhydroxylamines is of an importance synthetically both in the laboratory and in industry. Normally,aromatic amines and N-arylhydroxylamines are prepared through the reduction of the corresponding nitroarenes using Fe/HCl and alkali sulphide.However,these methods are environmental pollution protocols.Although catalytic hydrogenation is an environmentally friendly method for the reduction of aromatic nitro compounds,it suffers from some difficulties such as hydrodehalogenation,bad selectivity and higher demands for safety. Recently,catalytic transfer hydrogenation(CTH)Of nitroarenes has been developed.This method is environmentally friendly,chemoselective,and especially simple,compared to the traditional method.CTH of nitroarenes was researched in this study.(a)Iron-zirconium mixed oxide was used as catalyst in the hydrazine hydrate reduction of nitroarenes.The yields of aromatic amines were up to 83%-96%after reduction for 60-300 min.Chloro,cyano and ester groups remained intact during the reaction.Then,experiments were carried out to investigate the reuse of catalyst and effect of different aromatic nitro compounds.Also,sulphur-containing nitroarenes were reduced over iron-zirconium mixed oxide catalyst in the presence of hydrazine hydrate.The yields of aromatic amines were up to 91%-96%after reduction for 1.5-3 h;(b)The feasibility of the reduction of aromatic nitro compounds with propan-2-ol over mixed metal oxides catalyst was investigated.The results indicated that the relative content of aromatic amines were up to 66%-89%after reducing for 1.5-12 h in the presence of vanadium-containing aluminium-zinc mixed oxide;(c)Aromatic nitro compounds could be reduced to the corresponding amines in high yields(93%-99%)with hydrazine hydrate in the presence of commercial CoCl₂-6H₂O under refluxed condition in water/CH₃CN(v/v,7/3)and N-arylhydroxylamines(80%-93%)at room temperature in water/CH₃CN(v/v,2/3), respectively.The reaction could be completed within 1-9 h.Furthermore,many functional groups,such as chloro,nitrile,ester,and carbonyl groups,were tolerated.The reduction of sulphur-containing nitroarenes was carried out in the presence of CoCl₂·6H₂O catalyst using hydrazine hydrate.The results demonstrate that 96%-99%relative content of aromatic amines was obtained after 0.5-1.5 h;(d)Arylhydroxylamines were prepared successfully by CTH of the corresponding nitroarenes using the Zn/HCOONH₄/CH₃CN/ultrasound system.The yields of N-arylhydroxylamines were up to 64%-97%after reduction for 40-180 min at room temperature.In the case of 3-chloronitrobenzene,the effects of various operating parameters on this reaction,such as different commercial zinc,solvent,reaction temperature and substituents have been investigated in detail.And two most important factors of the reduction were considered as zinc and solvent.