Sodium Arenetellurolate Catalyzed Selective Conversion of Nitroaromatics to Aromatic Azoxy or Azo Compounds and Its Application for Facile Preparation of 3,3'- and 4,4'-Bisazobenzenes from (3- and 4-Nitrophenyl)acetylenes

Article abstract of DOI:10.1021/jo00278a034

Treatment of aromatic nitro compounds with sodium borohydride in alkaline ethanol in the presence of a catalytic amount of diaryl ditelluride at room temperature affords the corresponding azoxy compounds selectively in fair to excellent yields.Under reflux aromatic azo compounds are obtained as major products.In situ generated sodium arenetellurolate (ArTeNa) is the active species to reduce nitroaromatics into aromatic nitroso compounds, the latter being easily converted into azoxy compounds in alkaline ethanol.Higher temperature enables ArTeNa to reduce the initially produced azoxy compounds into azo compounds.A new vinylic telluride having an azo group in the molecule, 3,3'-bis<β-(aryltelluro)vinyl>azobenzene, was prepared in one pot in 66-91percent isolated yield by treating (3-nitrophenyl)acetylene with a stoichiometric amount of ArTeNa in alkaline ethanol at reflux temperature, the structure of which was determined unambiguously by X-ray crystallography.The corresponding 4, 4'-isomer was similarly prepared, but in lower yield.