Molecular Organization of Reagents in the Kinetics and Catalysis of Liquid-Phase Reactions: XI. Manifestation of the Structure of Solution in the Kinetics of Water Addition to Isocyanate in Water–Dioxane Mixtures

Abstract

Evidence for the structural effect of liquids associated by hydrogen bonds on the kinetics of molecular reactions was experimentally found. The kinetics of hydrolysis of (phenylaza)phenyl isocyanate in water–dioxane mixtures was studied at various temperatures and in the presence of structure-making and structure-breaking additives. The apparent order γ of reaction with respect to water concentration increased with temperature because of the partial breaking of the H-bond solution structure. It was found that the value of γ was affected by salt additives, for which positive (Et4NCl) or negative (KI) hydration is typical. This hydration resulted in strengthening or partially breaking the H-bond structure of water, respectively. It follows from the kinetic data that the addition of 0.1 mol/l Et4NCl was equivalent to a decrease in the solution temperature by 6 to 7°С, whereas the addition of 0.1 mol/l KI was equivalent to an increase in the temperature by 5 to 6°С. The effect of poly(ethylene oxide) additives (which stabilize the structure of water) on the value of γ was similar to the effect of the tetraethylammonium salt, which is characterized by positive hydration.