Solvent-induced changes in nitrosation mechanisms. Part 3. The effects of tetrahydrofuran–water and dimethyl sulfoxide–water mixtures on the nitrosation of ureas

Abstract

Kinetic studies of the nitrosation of 1,3-dimethylurea and 2-imidazolidone in tetrahydrofuran–water and dimiethl sulfoxide–water mixtures have been carried out. In tetrahydrofuran–water mixtures, the results obtained show that the kinetic characteristics of the reaction depend on the proportion of tetrahydrofuran in the medium. At low concentrations of organic solvent, the reaction is not catalysed by chloride ions and the reaction mechanism is probably the same as in pure water. At very high proportions of tetrahydrofuran (more than 80% by weight), there is a change in the reaction mechanism. Halide ions catalyse the process, which is interpreted in terms of formation of the corresponding nitrosyl halides which act as efficient nitrosating agents of ureas. In dimethyl sulfoxide–water mixtures the results obtained show that the addition of the organic solvent up to 85% by weight of dimethyl sulfoxide inhibits the reaction rate, which increases slightly upon further increasing the proportion of dimethyl sulfoxide. However, unlike other organic solvents, in dimethyl sulfoxide–water mixture we did not observe catalysis by halide ions. The reaction mechanism seems to be the same as in pure water, with the proton transfer from the protonated nitroso compound to the medium being the rate limiting step.