Studies on internal nitroso group transfer. Nitrosation of thiomorpholine

Abstract

The kinetics of nitrosation of thiomorpholine have been studied under different experimental conditions. At low nitrite concentration and high acidity the reaction rate is first order with respect to nitrite and thiomorpholine and independent of acidity. The results are interpreted through a mechanism in which the S-nitroso intermediate with a deprotonated amino group must acquire a boat conformation to facilitate the migration of the NO group from the sulphur to the nitrogen atom. The mechanism is supported by the low isotope effect observed when the reaction is studied in D₂O. In the pH range 2.3–3.6 and high nitrite concentration, the reaction rate is second order with respect to nitrite, the accepted mechanism being the nitrosation of deprotonated thiomorpholine by dinitrogen trioxide.