Medium Effect on the Reaction of N‐Butyl‐2,4,6‐trinitroaniline with NaOH
The kinetics of the reaction of N-butyl-2,4,6-trinitroaniline (3) with NaOH have been studied in 10 and 60 % 1,4-dioxane/H2O at 25 °C. In both cases, several processes were observed. In 10 % 1,4-dioxane/H2O the only product formed was 2,4,6-trinitrophenol (4), whereas in 60 % 1,4-dioxane/H2O a mixture of 4 and 5,7-dinitro-2-propyl-1H-benzimidazole 3-oxide (5) was observed in ratios that depend on the HO– concentration. A mechanism involving the formation of σ complexes through the addition of one or two HO– anions to unsubstituted ring positions is proposed for 2,4,6-trinitrophenol formation. The presence of these complexes was confirmed by NMR studies in 60 % [D8]1,4-dioxane/D2O. The mechanism suggested for the formation of the N-oxide includes the cyclization of an N-alkylidene-2-nitrosoaniline-type intermediate as the rate-determining step. The decrease in solvent polarity produces a decrease in the observed rate constant for the formation of 4 of about one order of magnitude making the cyclization reaction a competitive pathway. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)