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.
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.