A Nuclear Magnetic Resonance Study on Ligand Exchange Reaction in U(Ⅵ) Nitrato Complex with n-Octyl(phenyl)- N, N-Diisobutylcarbamoylmethylphosphine Oxide in Acetone Containing Oxalic Acid

摘要

In order to examine the effect of oxalic acid(H_2ox) on the exchange reaction of n-octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (oφcmpo) in U(Ⅵ) nitrato complex with oφcmpo, structural and kinetic studies have been carried out for the solutions prepared by dissolving UO_2(NO_3)(oφcmpo), oφcmpo, and H_2ox in CD_3COCD_3 using ~(31)P and ~(13)C NMR method. The number of coordinated oφcmpo was determined to be 2 by the area integration of ~(31)P NMR signals of free and coordinated oφcmpo. From the area integration of ~(13)C signals of free H_2ox and coordinated oxalate(Cox), the number of Cox was estimated to be 1. Hence, the complex with composition ratio of UO_2~(2+) : oφcmpo : Cox=1: 2 :1 was supposed to be formed in the present solution system. The exchange rate of oφcmpo in this complex was found to show a first-order dependence on the free oφcmpo concentrations and to decrease with increasing free H_2ox concentrations. From these results, it is proposed that the exchange reaction of oφcmpo proceeds through the interchange (Ⅰ) mechanism and that the retardation effect of free H_2ox is due to the formation of outer-sphere complex.