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Malonamide derivatives, which are the most extensively investigated extractants for solvent extraction of lanthanides, actinides, and platinum group metal ions, were deuterated by using Pd/C and Rh/C catalysts in a D2O/2-propanol mixture. This method replaces 1H atoms in the malonamides with 2H atoms at a controllable deuteration rate. The maximum rate reached about 75%, determined by nuclear magnetic resonance and electrospray ionization – mass spectrometry. The extraction behavior of metal ions by the malonamides was unchanged by the deuteration. Deuterated malonamides are a powerful tool for fundamental research on solvent extraction systems and for structural analysis of organic phases. The large difference in the cross section of coherent neutron scattering between 1H and 2H leads to a large difference in neutron scattering length density of malonamide derivatives before and after the deuteration. Therefore, using deuterated malonamides in small-angle neutron scattering and neutron reflectivity studies may help to reveal the microscopic structure of the specific solute species in the bulk organic phase and at the liquid–liquid interface, respectively. In this paper, we report the advantage of the deuterated malonamides for a contrast-matching method in the SANS experiment. This deuteration method could be generalized and extended to a wide variety of extractant molecules.

We compare the extraction performance of new extractant, fluorous phosphate tris(4,4,5,5,6,6,7,7,7-nonafluoroheptyl) phosphate (TFP) in the fluorinated diluent perfluorohexane, for Zr(IV) with a conventional organic extractant, tri-n-butyl phosphate (TBP) in n-octane. It is surprising that fluorinating TBP to TFP improved the extraction performance, as normally fluorinating the hydrocarbon substituents on neutral extractants tends to decrease the extraction strength. We examined the origin of the superior extraction performance of TFP by analyzing the equilibrium of the chemical reaction during the extraction. The equilibrium reaction of Zr(IV) with TFP is ZrNO34aq+3TFPflu ⇌ZrNO34TFP3flu, whereas that with TBP is ZrNO34aq+2TBPorg ⇌ZrNO34(TBP)2org. Phosphorus-31 nuclear magnetic resonance and infrared spectroscopy measurements of TFP and TBP showed similar electron densities at the phosphorus atom and vibration modes of the P=O group, implying similar coordination to Zr(IV). In addition, the concentrations of all components (Zr(IV), HNO3, and water) in the fluorous and organic phases after solvent extraction were evaluated by inductively coupled plasma-mass spectrometry, ion chromatography, and Karl-Fischer titration. The concentrations of water and HNO3 molecules in the fluorous phase become low during the Zr(NO3)4(TFP)3 extraction, indicating that water and HNO3 molecules do not preferentially interact with Zr(NO3)4(TFP)3 in contrast to Zr(NO3)4(TBP)2 in n-octane We speculate that the excellent performance originated from the stability of Zr(NO3)4(TFP)3 in the fluorous phase. Hence, TFP is expected to be used as an alternative extractant to TBP.

We performed neutron polarization analysis (NPA) of extracted organic phases containing complexes, comprised of Zr(NO3)4 and tri-n-butyl phosphate, which enabled decomposition of the intensity distribution of small-angle neutron scattering (SANS) into the coherent and incoherent scattering components. The coherent scattering intensity, containing structural information, and the incoherent scattering compete over a wide range of magnitude of scattering vector, q, specifically when q is larger than q* ≈ 1/Rg, where Rg is the radius of gyration of scatterer. Therefore, it is important to determine the incoherent scattering intensity exactly to perform an accurate structural analysis from SANS data when Rg is small, such as the aforementioned extracted coordination species. Although NPA is the best method for evaluating the incoherent scattering component for accurately determining the coherent scattering in SANS, this method is not used frequently in SANS data analysis because it is technically chall...