Michael R. Crampton and Simon D. Lord
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 σ-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.
104 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.