Electrophilic aromatic substitution in substituted anilines; kinetics of the reaction with 4,6-dinitrobenzofuroxan

Kinetic results are reported for reaction of aniline and six of its N- and ring-substituted derivatives with 4,6-dinitrobenzofuroxan (DNBF) in water - dimethyl sulfoxide mixtures. In acidic solution sigma-adducts, the result of electrophilic substitution in the anilines, are formed with bonding between a ring-carbon atom of the anilines and the 7-position of DNBF Reaction normally occurs at the 4-position of the aniline unless this carries a substituent, when reaction occurs at the 2-position. A value of 2.0 for k(H)/k(D), the kinetic isotope effect, indicates that in the reaction with aniline bond formation is largely rate determining in the substitution pathway. The results allow estimates to be made for the pK(a) values relating to carbon protonation of the anilines.