Solvent effects on the rate of the reaction of 2,4-dinitrofluorobenzene with the ethyl ester of tyrosine

Abstract

The reaction of 2,4-dinitrofluorobenzene with the ethyl ester of tyrosine was studied in 11 solvents; values of k_obs and k₂(second order) were determined. The k₂ values increase in the order: benzene, 1,2-dichloroethane, ethyl acetate, dioxane, acetonitrile, methanol, propylene carbonate, ethanol, propan-2- ol, NN-dimethylformamide, and dimethyl sulphoxide. The k₂ values are strongly dependent on the Lewis basicity of the solvents. A correlation analysis is made, the multiparameter equations of Koppel and Palm, of Krygowski and Fawcett, and of Kamlet and Taft all being examined. The activation parameters in eight solvents were also determined, and a linear correlation between ΔS^‡ and donor number DN is discussed.