Reactivity and selectivity control in the substitution reactions of nitro group and fluorine in 3-R-5-nitrobenzotrifluorides with aryloxide and arylthioxide ions

Abstract

The relative mobility of nitro group and fluorine in 3,5-dinitro- and 3-fluoro-5-nitrobenzotrifluorides under the action of both phenols and thiophenols in the presence of potassium carbonate in DMF at 40–95 °C was studied by the competitive reactions method. Correlation analysis of the relative rate constants, k/kF, and the activation parameter differences, ΔΔH≠ and ΔΔS≠, of the competitive reactions was carried out. The displacement selectivity of the nitro group and fluorine depends on the nature of the nucleophile and is characterized by isokinetic ratios: the nitro group mobility increases compared with that of fluorine with increase in the reaction temperature and the decrease in the nucleophile basicity. There are good linear relationships between Brø nsted coefficient difference ΔβNuc and reciprocal temperature, 1/T, enthalpy, ΔΔH≠, and entropy, ΔΔS≠, differences, suggesting isokinetic ratios in these reactions. The isokinetic temperatures are lower than the experimental temperature range, indicating that the displacement selectivity is controlled by entropy. Copyright © 2000 John Wiley & Sons, Ltd.