Kinetic and equilibrium studies of the ambident reactivity of aniline, and some derivatives, towards 4,6-dinitrobenzofuroxan

The reactions of aniline and its derivatives at the 7-position of 4,6-dinitrobenzofuroxan (DNBF) may result in rapid reaction via the nitrogen centre to give anionic sigma-adducts. Equilibrium constants for these reactions in DMSO are reported and correlate with pK(a) values of the corresponding anilinium ions. Slower reactions are observed involving electrophilic substitution by DNBF at ring-carbon atoms of the aniline derivatives; rate constants are reported. These reactions produce zwitterionic carbon-bonded sigma-adducts which, in the presence of excess aniline, are in rapid equilibrium with deprotonated forms. Equilibrium constants for this acid-base process have been measured and indicate that the negatively charged DNBF moiety is electron withdrawing relative to hydrogen.