MECHANISM OF MOLECULAR NITROGEN REDUCTION TO HYDRAZINE BY BIVALENT CHROMIUM HYDROXIDE

The effect of the water concentration on the rates of the hydrazine an d hydrogen formation in the reactions involving Cr(II) hydroxide is st udied in alkaline CH3OH-H2O and CH3OD-D2O mixtures. It was shown that the rate of nitrogen reduction to hydrazine in the deuterated solvent is higher than that in the nondeuterated solvent in the range [H2O] = 1.32-4.10 mol/l. The rate constant ratio k(D)/k(H) for the hydrogen ev olution is higher than unity at [H2O] > 2.5 and lower than unity at [H 2O] < 2.5 mol/l. In the protium system, HD is found to be formed in th e presence of D-2. A conclusion is made that the rate of the hydrazine formation is determined by the step of intramolecular transfer of the hydride atom to the coordinated nitrogen molecule. A kinetic model pr oposed explains adequately the influence of the water concentration on the k(D)/k(H) value for both reactions. The structure of the active c enter is discussed.