Meisenheimer complex formation between 4,6-dinitrobenzofurazan 1-oxide and primary, secondary and tertiary aromatic amines

The uncatalysed formation of stable 1 : 1 Meisenheimer complexes between primary, secondary and tertiary aromatic amines and 4,6-dinitrobenzofurazan 1-oxide has been investigated. The thermodynamic product is derived from reaction through the aromatic carbon para or, if this position is substituted, ortho to the amino group of the aromatic amine. The complexes are stable to acid but react in aqueous potassium hydrogen carbonate solution or with aliphatic or aromatic amines to give crystalline salts of the complexes. In the presence of 1,4-diazabicyclo[2.2.2]octane, aniline reacts with 4,6-dinitrobenzofurazan 1-oxide to give an unstable nitrogen-bonded complex which is slowly converted into the carbon-bonded complex. The scope of the complexation reaction has been investigated and some of the mechanistic implications of the results are discussed.