Nitrosation of amines in non-aqueous solvents: difference between N-N=O and O-N=O Nitroso donors

A kinetic study has been carried out on nitroso group transfer from substituted N-methyl-N-nitroso-benzenesulfonamides to different secondary amines: pyrrolidine, piperidine, Nmethylpiperazine,and morpholine in cyclohexane. The observed pseudo-first-order rate constant kobs shows a linear and quadratic dependency on the amine concentration with the existence of a primary kinetic isotope effect. Experiments carried out at different temperatures show Arrhenius-type behavior. Addition of isopropylamine(iPrNH2) to the reaction medium produces an increase in kobs. In the presence of a high iPrNH2 concentrations the influence of secondary amine concentration on kobs shows the disappearance of the quadratic dependency of kobs on the secondary amine. These results would be compatible with an addition-elimination mechanism, similar to that observed for the aminolysis of thealkyl nitrites in apolar solvents. The observed behavior in the presence of 18-crown-6 is very different, however. Addition of crown ether catalyses the reaction of aminolysis of alkyl nitrites insofar as it does not alter the rate of the nitroso group transfer from N-nitrososulfonamides. This behavior has been interpreted in terms of a concerted reaction mechanism through cyclical transition states, with four or six centers, involving one or two molecules of secondary amine. Addition of iPrNH2 to the reaction medium causes the appearance of a third reaction path, which emerges through a mixed transition state formed by a molecule of a secondary amine and a molecule of isopropylamine