Electrochemical Synthesis Of Aromatic Amine Compounds

Aromatic amine compounds were found wide applications in chemical, pharmaceutical and agricultural industries in the synthesis of intermediates,medical drugs,dyestuff,and so on.The reaction of synthesis of aromatic amine compounds from aromatic nitro compounds is one of important organic synthesis unit reactions. The conventional methods of aromatic amine compounds production mainly include: the powdered iron/sodium sulfide reduction method;the catalytic hydrogenation method and the hydrazine hydrate reduction method.The conventional methods, especially the powdered iron/sodium sulfide reduction method,bring much liquid waste and waste residue.Consequently,alternative eco-friendly syntheses of aromatic amine compounds to the classical methods have been studied and proposed in the recent few years.Electrochemical synthesis of aromatic amine compounds is one of important green synthesis routes,which are easy to control,clean,little byproduct and environment friendly technology to the chemical industry.In addition,electrosynthesis,which studies the synthesis of organic compound with electrochemical technologies and methods,uses electron as reagent to replace the conventional redox agent to carry out the synthesis of organic compound.It tries to avoid pollution from the beginning.So, it could be propitious to produce it in industry.The paper is divided into four main parts.In the first part,electrosynthesis of 1,5-diaminenaphthalene from 1,5-dinitronaphthalene was studied.At room temperature,the electrochemical reduction behavior of 1,5-dinitronaphathlene has been studied on a Cu electrode by cycle voltammertry in DMF-water solution.It was an irreversible reaction controlled by diffusion.1,5-Dinitronaphthalene exhibited two successive waves in the DMF-water solution which were corresponding to the two nitro-group electroreduction.The transfer coefficients of the reaction were calculated. The value ofα₁ andα₂ was between 0.275～0.335 and 0.360～0.437 respectively. Influence of electrolysis potential(E),the concentration of 1,5-dinitronaphthalene(c¹) and the concentration of sulfuric acid(c²),the passed charge(Q),volume ratio of solvent to water(Y)was investigated to optimize the electrolytic conditions,with the maximal yield to be 77%.Furthermore,the electrochemical reduction behavior of 1,5-dinitronaphthalene was studied in HMIMBF₄-DMF. In the second part,synthesis of 2-anisidine from 2-nitroanisole was studied.The synthesis was carried out in a room-temperature ionic liquid(RTIL) 1-butyl-3-methylimidazolium tetrafluorobrate(BMIMBF₄)with little water as hydrogen source,under mild condition.RTIL was worked as electrolyte and solvent that the volatile,toxic solvents,catalysts,as well as any additional supporting electrolyte were avoided.The maximal yield of 2-anisidine reached 51.3%on Cu-grap hite couple electrodes under potentiostatic electrolysis at -1.0 V(vs.SCE)until 6 F·mo1^-1of charge was passed at 323 K,which offers a new and clean route to synthesis of 2-anisidine.The reduction behavior of 2-nitroanisole was studied in RTIL by cycle voltammertry.The diffusion coefficients of 2-nitroanisole in BMIMBF₄ were calculated to be 1.81×10^-6cm².s^-1.In the third part,The electrochemical reduction of 2-chloronitrobenzene was investigated in the room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluorobrate(BMIMBF₄)on a Cu disc microelectrode by using cyclic voltammetry and AC(Alternating Current)impedance method,taking some water as the resource of hydrogen.The results showed that the electroreduction of 2-chloronitrobenzene was a reaction mainly controlled by diffusion.The AC impedance plots at different potentials show that the reaction is controlled by both electrochemical polarization and diffusion processes,appeared at higher and lower frequencies respectively.With the increase of applied potentials,the semi-circles appeared at higher frequencies become smaller and smaller,and illustrated the easier carried out of the reaction.The diffusion coefficients of 2-chioronitrobenzene at various temperatures in BMIMBF₄ were calculated,which was corresponded to the Arrhenius equation,and the activation energy of diffusion of 2-chloronitrobenzene in BMIMBF₄ was also calculated to be 24.33 kJ·mol^-1.Influence of electrolysis potential,the concentration of 2-chloronitrobenzene and the passed charge was studied to optimize the electrolytic conditions,with the maximal yield to be 86.2%.In the fourth part,a novel electrochemical procedure for the synthesis of aromatic amine compounds from aromatic nitro compounds was developed in room temperature ionic liquids(RTILs)-H₂O.The electrochemical reduction behavior of aromatic nitro compounds has been studied on Cu electrode in RTILs-H₂O by cyclic voltammertry.The synthesis was carried out under mild and safe conditions in a divided cell.Substituted nitrobenzene with electron withdrawing group will be reduced at more positive potential,while these with electron donating group will be reduced at more negative potential.In addition,the reduction peak potential of nitro group of o-nitrobenzene shifts more negative due to the steric hindrance.Influence of the working potential,the anodal materials and the nature of ionic liquid was examined.The method of synthesis aromatic amines in ionic liquid was generality. This method provided a new,wide and clean route to synthesis aromatic amine compounds.Meanwhile,it was concerned that electrosynthesis have an advantage of high selective of production.