Synthesis Of Unsymmetrical Azoxyarenes Based On The Condensation Of Aromatic Amines And Nitrosoarenes

Azoxyarenes have been widely applied in dyes,pigments,pharmaceuticals,food additives,and liquid crystal materials due to their conjugated system and polar functionality.Selective oxidation of aromatic amines and reduction of nitroarenes are the most common methods for the preparation of azoxy compounds.However,azoxy compounds obtained by the above two routes are symmetric rather than unsymmetrical aromatic azoxy compounds.It is well known that unsymmetrical aromatic azoxy compounds play a key role in the applications of pharmaceuticals and liquid crystal materials.Traditional synthetic methods in the production of unsymmetrical azoxybenzene still remain several drawbacks,such as low yields,low selectivity,and complicated operation.Therefore,it is of great significance to explore a highly efficient and practical method for the synthesis of unsymmetrical azoxy compounds.In this paper,we started our investigation by examining the reaction of cheap and commercially available aromatic amines and nitrosobenzene to obtain optimized reaction conditions,unsymmetrical azoxybenzene was constructed by dehydrogenation oxidation coupling,and the following three reaction systems were developed:?1?I₂/DABCO system:The reaction system uses inexpensive iodine as an oxidant and DABCO as the base to efficiently obtain unsymmetrical azoxybenzene under mild conditions.In addition,the reaction mechanism was further studied,and the reasonable mechanism of the reaction was proposed.?2?Ag₂O system:The reaction system uses commercially available Ag₂O as an oxidant,requires no additional additives,and uses environmentally friendly ethanol as the reaction solvent to obtain unsymmetrical azoxybenzene efficiently under mild conditions.?3?MC-Cu as a heterogeneous catalyst:Firstly,MC-Cu materials were prepared by in-situ co-doping method,and the material was successfully applied to the synthesis of unsymmetrical azoxybenzene as the catalyst.The reaction system can efficiently obtain unsymmetrical azoxybenzene under the catalytic amount of MC-Cu material.