Kinetics and mechanism of the Fischer–Hepp rearrangement. Part III. Rearrangement and denitrosation in the presence of urea and other nucleophiles

Abstract

Rate measurements and product analyses have been carried out for the reaction of N-methyl-N-nitrosoaniline in both hydrochloric and sulphuric acid in the presence of added urea, sulphamic acid, sodium azide, and aniline. From the variation of the observed first-order rate coefficient (k_obs) with urea etc., added N-methylaniline, added salts, and the changing acidity of the medium, together with the deuterium solvent isotope effect, a rate equation is established which is derived from a reaction mechanism involving concurrent rearrangement and (reversible) denitrosation. Features of the denitrosation reaction have been determined for the first time. In the presence of chloride (or bromide) ions the immediate product of denitrosation is N-methylaniline and nitrosyl chloride (or bromide) which then reacts rapidly with the added nucleophiles. The same mechanism, but involving the nitrous acidium ion H₂NO₂, is found for reaction in sulphuric acid. There is no evidence for a direct transnitrosation which does not involve the intermediacy of a free nitrosating agent either in hydrochloric or in sulphuric acid.