Abstract
The main result of reaction between 2-bromonitrobenzene and copper(I) oxide in boiling pyridine was Ullmanntype coupling, giving up to 70% of 2,2′-dinitrobiphenyl; other products were 2-nitrophenol (0–40%), nitrobenzene (0–70%), and bis-2-nitrophenylamine (ca. 1%), formed via 2-nitroaniline resulting from opening of the pyridine ring. Brief reaction of 1-bromo- or 1-chloro-2,4-dinitrobenzene under similar conditions produced 2,4-dinitroaniline. Reactions like those of 2-bromonitrobenzene were shown by some other ortho-nitrosubstituted aryl bromides or iodides, and by methyl ortho-iodobenzoate. If the appropriate element was added to reaction mixtures, biaryl formation (ArHal → ArAr) was suppressed in favour of formation of the aryl derivatives Ar2Hg, Ar2Se2(or Ar2Se), and Ar2Te. Good yields of the biaryl were produced by use of copper metal or copper(I) sulphide (also giving Ar2S) in place of the oxide, but not by copper(I) halides. Effects of various additives are reported and a mechanistic scheme is suggested.
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