Nucleophilic displacement reactions in aromatic systems. Part X. Kinetics of the reactions of substituted α-halogenopyridines with aniline, N-methyl-, and N-ethyl-aniline in ethanol or ethyl acetate, and of 1-fluoro-2,4-dinitrobenzene with aniline in various solvents. The influence of basic catalysts

Abstract

Rate coefficients for the reactions of 2-chloro- or -fluoro-3- or -5-nitropyridine with N-methylaniline in ethanol at 80° and for the reactions of 2-chloro-3-cyano- or 3-cyano-2-fluoro-5-nitropyridine with aniline, N-methyl-, or N-ethyl-aniline in ethanol at 20° have been determined. The effect of the initial concentration of the amine and of the concentration of added potassium acetate, acetic acid, or sodium perchlorate has been extensively investigated. Catalysis of the reactions of the fluoro-compounds (but not the chloro-compounds) by acetate ion is typical, except with aniline as nucleophile, but catalysis by the amine is not usually observed. The acetateion catalysis and the relative mobility of fluorine and chlorine in the various reactions are discussed in terms of the two-stage mechanism of nucleophilic aromatic substitution. The role of the amine and the occurrence of side reactions (ethanolysis and acetolysis) are also examined. Rate coefficients for the reactions of 2-chloro-3-cyano- or 3-cyano-2-fluoro-5-nitropyridine with aniline, N-methyl-, or N-ethyl-aniline in ethyl acetate (at various convenient temperatures) have also been measured. The reactions of the fluoro-compound (but not of the chloro-compound) are subject to strong catalysis by the amine. Rate coefficients have also been measured for the reactions of 1-fluoro-2,4-dinitrobenzene with aniline or N-methylaniline in methanol, ethanol, benzyl alcohol, ethyl acetate, or toluene. In the less polar solvents, pyridine or triethylamine catalyses the amination strongly, and catalysis by the reactant amine is also observed. All these results are discussed in terms of the two-stage mechanism.