Reaction of ethyl iodide with bromide ion. Kinetics, transfer enthalpies of anions and extended Brönsted relationships in acetonitrile + methanol and NN-dimethylacetamide + methanol mixtures

Abstract

Rate constants and activation parameters have been determined for the reaction of ethyl iodide plus bromide ion in acetonitrile + methanol and NN-dimethylacetamide + methanol mixtures. Single-ion transfer enthalpies have also been determined in these two solvent mixtures for the ions Br^–, I^–, ClO^–₄ and (n-Bu)₄)B^– on the basis of tetra-n-butylammonium/tetra-n-butylborate exchange. Experimental analysis and model calculations indicated that the halide-ion solvation enthalpy is a composite of the hydrogen-bonding energy and of the ‘more physical’ interaction energy. The physical meaning of the abnormal coefficient of the extended Brönsted relationships observed for the present reactions is discussed by dissecting anion transfer enthalpies into their constituent terms.