The reaction of 2,4-dinitrofluorobenzene with aniline, cyclohexylamine, and 1,2-diaminocyclohexanes in aprotic solvents. A new approach to the ‘dimer mechanism’

The reaction of 2,4-dinitrofluorobenzene (DNF) with aniline in toluene and in chloroform at 35 °C shows a third-order kinetic dependence on [amine]. In hydrogen-bond acceptor (HBA) solvents, an important rate increase, and a second-order dependence on [amine], are observed. Finally, the reaction shows a second-order dependence on non-nucleophilic tertiary amines. All these results are fully consistent with the previously proposed ‘dioner nucleophile mechanism.’Another approach towards confirming the mechanism was designed: a system where an ‘intramolecular dimer nucleophile’ is possible. The reactions of DNF with cyclohexylamine, and with cis-and trans-1,2-diaminocyclohexane, were studied in toluene, and also in toluene–methanol mixtures in some cases. The kinetic order observed, as well as the enhanced reactivity of the cis isomer and the solvent effects are new evidence in favour of the ‘dimer nucleophile’ mechanism. The results cannot be explained by other, alternative mechanisms.