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

Abstract

In order to examine the effect of oxalic acid(H₂ox) 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 UO₂(NO₃)₂(oφcmpo), oφcmpo, and H₂ox in CD₃COCD₃ using ³¹P and ¹³C NMR method. The number of coordinated oφcmpo was determined to be 2 by the area integration of ³¹P NMR signals of free and coordinated oφcmpo. From the area integration of ¹³C signals of free H₂ox and coordinated oxalate(Cox), the number of Cox was estimated to be 1. Hence, the complex with composition ratio of UO²⁺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 H₂ox 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 H₂ox is due to the formation of outer-sphere complex.