Metal ions and complexes in organic reactions. Part XI. Reactions in pyridine between copper species and aryl halides, in particular between copper(I) oxide and 2-bromonitrobenzene

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.