A nuclear magnetic resonance study on ligand exchange reaction in U(VI) nitrate complex with n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide in acetone containing oxalic acid

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) nitrate 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 UO22+: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. (author)