Amines as leaving groups in nucleophilic aromatic substitution reactions. Part 5.~1 Substitution vs. N-oxide formation in the reaction of N-n-butyl-2,6-dinitroaniline with hydroxide ions

摘要

A kinetic study of the reaction of N-n-butyl-2,6-dinitroaniline 1 with NaOH was carried out in 10% 1,4-dioxane-water at 25 deg C, giving 2,6-dinitrophenol 2 and 7-nitro-2-n-propyl-1H-benzimidazole 3-oxide 3 in ratios depending on the HO~- concentration. The rate constant for the formation of 2 is second order in HO~- concentration while that of 3 is first order then, the relative amount of 2 : 3 formed increases with HO~-. A mecahnism involving the formation of a #sigma# complex by addition of HO~- to an unsubstituted position of the aromatic ring is proposed for 2,6-dinitrophenol formation. The mechanism suggested for the formation for the formation of the N-oxide requires the deprotonation of the substrate.