Kinetic study of the nitrosation reaction of 1,3-dimethylurea in dioxane–water mixtures

Abstract

The nitrosation of dimethylurea has been studied in dioxane–water mixtures showing that the kinetic characteristics of the reaction depend on the proportion of dioxane in the medium. Adding dioxane to pure water causes the reaction rate to decrease, and pass through a minimum as a certain concentration of dioxane is reached. The further addition of dioxane increases the reaction rate steadily. At low concentrations of dioxane the system shows the behaviour seen in water, i.e. catalysis by bases and not by nucleophiles, suggesting proton transfer as the slow step. At very high proportions of dioxane, halides and thiocyanate catalyse the process, which is interpreted in terms of the formation of the corresponding nitrosyl halides which may act as efficient nitrosating agents towards the urea. The observed order of efficiency of the catalysts is the opposite to that seen in nitrosation or diazotization processes in water.