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

Anisole can be nitrosated in good yield under the acidic and anaerobic cond itions previously reported for methylbenzenes. The product, 4-nitrosoanisol e, is slowly converted into 4-nitrosophenol in acetic-sulfuric acid mixture s. The decrease in the rate constant for this reaction with increasing conc entration of nitrosonium ion leads to an estimate of the stability constant of the complex between 4-nitrosoanisole and nitrosonium ion. Stability con stants for the similar complexes formed by 4-nitrosotoluene and 1,3-dimethy l-4-nitrosobenzene with nitrosonium ion in trifluoroacetic acid have been d etermined by UV spectroscopy. Restricted rotation about the bond between ni trogen and aromatic carbon is evident from the H-1 NMR spectra of the compl exes; activation parameters for the rotation are reported and compared with similar data in the literature for restricted rotation in uncomplexed arom atic nitroso compounds.