Kinetics and mechanism of the Fischer–Hepp rearrangement and denitrosation. Part VI. The relative reactivity of a number of nitrogen-containing species towards nitrosation, and further evidence against an intermolecular mechanism for the rearrangement

Abstract

The constant value found for the rearrangement: denitrosation product ratio from N-methyl-N-nitrosoaniline in sulphuric acid containing a wide variety of ‘nitrite traps’ at various concentrations at any one acidity, argues very strongly against a mechanism for the Fischer–Hepp rearrangement involving prior denitrosation and C-nitrosation of N-methylaniline (NMA) by the free nitrosating agent. The result is however consistent with a previously proposed intramolecular mechanism which occurs concurrently with denitrosation. The observed rate constant k₀ is decreased as NMA is added, thus reversing the denitrosation step. From the variation of k₀ with [NMA] it is possible to obtain values for the relative reactivity towards nitrosation, of a number of ‘nitrite traps,’ urea, sulphamic acid, hydroxylamine, hydrazoic acid, aniline, and hydrazine. This establishes the reactivity sequence of these compounds towards nitrosation by nitrosyl chloride, nitrosyl bromide, and the nitrous acidium ion. The observed selectivity of these three reagents NOBr > NOCl > H₂[graphic omitted]O₂ is discussed in terms of their relative reactivities.