SOLVENT-INDUCED CHANGES IN NITROSATION MECHANISMS .3. THE EFFECTS OF TETRAHYDROFURAN-WATER AND DIMETHYL SULFOXIDE-WATER MIXTURES ON THE NITROSATION OF UREAS

Kinetic studies of the nitrosation of 1,3-dimethylurea and 2-imidazoli done dagger in tetrahydrofuran-water and dimethyl sulfoxide-water mixt ures have been carried out. In tetrahydrofuran-water mixtures, the res ults obtained show that the kinetic characteristics of the reaction de pend on the proportion of tetrahydrofuran in the medium. At low concen trations 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 t he process, which is interpreted in terms of formation of the correspo nding nitrosyl halides which act as efficient nitrosating agents of ur eas. In dimethyl sulfoxide-water mixtures the results obtained show th at the addition of the organic solvent up to 85% by weight of dimethyl sulfoxide inhibits the reaction rate, which increases slightly upon f urther increasing the proportion of dimethyl sulfoxide. However, unlik e other organic solvents, in dimethyl sulfoxide-water mixtures 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 proton ated nitroso compound to the medium being the rate limiting step.