The use of radioisotopes in studies of reaction mechanism. Part I. Reaction order and activation parameters of iodide exchange in 1-iodo-2,4-dinitrobenzene

Abstract

The exchange reaction between iodide ion and 1-iodo-2,4-dinitrobenzene in methanol has been reinvestigated in a series of kinetic studies using a modified experimental technique. It has been shown that, contrary to earlier published work but in accordance with theoretical expectations, the reaction is overall second-order, being first-order with respect to each reagent. The Arrhenius activation energy of 22·8 kcal. is significantly higher than previously published values and in reasonable agreement with the value of ΔE* calculated by Miller's method for a bimolecular mechanism. It supports further the existence of a heavy-atom interaction mildly reducing the value of ΔE* below that calculated but with compensating reduction in ΔS*.