Katalytische Effekte bei den Reaktionen von 2, 4-Dinitrofluorbenzol mit Benzylamin und N-Methylbenzylamin in Benzol. 6. Mitteilung über nucleophile aromatische Substitutionsreaktionen

• (1) The rates of reaction of 2,4-dinitrofluorobenzene with benzylamine and with N-methylbenzylamine have been measured in benzene solution, with and without the addition of pyridine or 1, 4-diaza-bicyclo2.2.2]octane (DABCO) as catalyst.
• (2) Both reactions are catalyzed by the reacting amine, by pyridine and by 1, 4-diaza-bicyclo2.2.2]octane.
• (3) Whereas the dependence on base concentration is linear in the case of N-methyl-benzylamine, the rate constants are curvilinearly related to base concentration in the reaction with benzylamine. Steric effects are shown to be responsible for this different behaviour, which is easily understood in terms of the two-step intermediate mechanism (eq.1) for nucleophilic aromatic substitutions.
• (4) Part of the pyridine catalysis has to be attributed to a medium effect, as can be shown directly in the reaction involving benzylamine.
• (5) The sensitivity of both reactions to base catalysis is much greater than that of the reaction of piperidine with 2, 4-dinitrofluorobenzene, but is found to be considerably smaller than in the reaction of p-anisidine with the same substrate, thus suggesting a correlation between the basicity of the reacting amine and the sensitivity of the reaction to base catalysis.