Effect of Protic Solvent on Pyrolysis of Sulfimides

Abstract

Effect of protic solvents such as methanol on the pyrolysis of S-ethyl-S-phenyl-N-tosylsulfimide (SN [1]), S-ethyl-S-2-pyridyl-N-tosylsulfimide (SN [2]), and 2-(N-tosylethanesulfinimidoyl)pyridine 1-oxide (SN [3]) were studied in comparison with those of aprotic solvents, benzene and 1, 4-dioxane.
The relative rate in benzene: 1, 4-dioxane: methanol for the pyrolysis of SN (1) was 8.5: 5.5: 5.1 at 100°C. The activation parameters of SN [1] in methanol were Ea=115.1kJ/mol and ΔS&^ne;=-41.0 J.K-1mol-1. The E_a value was similar to that for SN [3] or S-phenyl-S-(1- and 2-phenylethyl)-N-tosylsulfimides [4] whereas ΔS&^ne; was about 1/5 that for SN [3] The isotope effect in methanol, k(_MeOH)/k(_MeOD), on the pyrolysis rates of SN [1]was about 0.82, while those of SN [2] and SN [3] were found to be nearly unity. The relations between log [MeOH] and log k for SN [1] and SN [3] gave straight lines with slopes of -O.45 and -O.58, respectively. The substituent effects gave linear Hammett correlations with a positive slope in all solvents. The ρ-values were O.792 in benzene, O.809 in 1, 4-dioxane and 0.851 in methanol. The retardation of the pyrolysis of sulfimide in the protic solvent may be ascribed to the formation of hydrogen bond between the protic solvent and the nitrogen atom of sulfimide function, of the substrate in the ground state.