Nitrosation of anisole, stability constants of complexes of the nitrosonium ion with aromatic nitroso compounds, and NMR studies of restricted rotation in the complexes

Abstract

Anisole can be nitrosated in good yield under the acidic and anaerobic conditions previously reported for methylbenzenes. The product, 4-nitrosoanisole, is slowly converted into 4-nitrosophenol in acetic–sulfuric acid mixtures. The decrease in the rate constant for this reaction with increasing concentration of nitrosonium ion leads to an estimate of the stability constant of the complex between 4-nitrosoanisole and nitrosonium ion. Stability constants for the similar complexes formed by 4-nitrosotoluene and 1,3-dimethyl-4-nitrosobenzene with nitrosonium ion in trifluoroacetic acid have been determined by UV spectroscopy. Restricted rotation about the bond between nitrogen and aromatic carbon is evident from the ¹H NMR spectra of the complexes; activation parameters for the rotation are reported and compared with similar data in the literature for restricted rotation in uncomplexed aromatic nitroso compounds.