Kinetic and equilibrium studies of sigma-adduct formations and nucleophilic substitution in the reactions of trinitro-activated benzenes with aliphatic amines in acetonitrile

Rate and equilibrium constants are reported for reactions in acetonitrile of butylamine, pyrrolidine and piperidine with 1,3,5-trinitrobenzene, 1, and with ethyl 2,4,6-trinitrophenyl ether, 4a, and phenyl 2,4,6-trinitrophenyl ether, 4b, Rapid nucleophilic attack at unsubstituted ring-positions may yield anionic sigma-adducts via zwitterionic intermediates, while slower attack at the 1-position of 4a and 4b may lead to substitution to give 2,4,6-trinitroaniline derivatives. Base catalysis in the substitution reaction reflects rate-limiting proton transfer which may be from the zwitterionic intermediates to amine in the case of 4b, or from a substituted ammonium ion to the ethoxy leaving group in the case of 4a. Comparisons with values in DMSO indicate that values of overall equilibrium constants for adduct formation are ca. 10(4) lower in acetonitrile, while rate constants for proton transfer are ca, 10(4) higher, These differences may reflect strong hydrogen-bonding between DMSO and -NH+ protons in ammonium ions and in zwitterions, In acetonitrile homoconjugation of substituted ammonium ions with free amine is an important factor.