Kinetics of the reaction between 2,4-dinitrophenol and tri-n-octylamine in chlorobenzene solution. Diffusion and other Rate-limiting Factors

Abstract

The kinetics of the reaction between 2,4-dinitrophenol and tri-n-octylamine in chlorobenzene solution have been investigated by a microwave temperature-jump technique. The rate constant is about 30 times smaller than the value calculated from the Smoluchowski treatment for a diffusion-controlled reaction. The activation enthalpy is slightly negative (ΔH^{[graphic omitted]}=–6.7 ± 2 kJ mol^–1 or –1.6 ± 0.5 kcal mol^–1). This is strong evidence against a one-step mechanism. A three-step mechanism accommodates the results. For this mechanism the significant fact about ΔH^{[graphic omitted]} is that it is lower than the viscosity-controlled value, rather than the fact that it is negative.