Kinetic and equilibrium studies of σ-adduct formation and nucleophilic substitution in the reactions of trinitro-activated benzenes with aliphatic amines in acetonitrile
作者:Michael R. Crampton、Simon D. Lord
DOI:10.1039/a603707k
日期:——
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 Ï-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. 104 higher. These
differences may reflect strong hydrogen-bonding between DMSO and
âNH+ protons in ammonium ions and in zwitterions. In
acetonitrile homoconjugation of substituted ammonium ions with free amine
is an important factor.
在乙腈中报道了丁胺、吡咯烷和哌啶与1,3,5-三硝基苯(1)以及2,4,6-三硝基苯醚(4a)和苯基2,4,6-三硝基苯醚(4b)反应的速率和平衡常数。未取代环位的快速亲核攻击可能通过双电离中间体形成阴离子σ-加合物,而在4a和4b的1位进行较慢攻击可能导致取代反应,形成2,4,6-三硝基苯胺衍生物。取代反应中的碱催化反映了速率限制的质子转移,这可能是从双电离中间体到胺(在4b的情况下),或者是从取代铵离子到乙氧基离去基(在4a的情况下)。与DMSO中的数值比较表明,在乙腈中,加合物形成的总体平衡常数值约低104倍,而质子转移的速率常数约高104倍。这些差异可能反映了DMSO与铵离子和双电离离子中–NH+质子之间的强氢键作用。在乙腈中,取代铵离子与游离胺的同源结合是一个重要因素。