Deuterated Malonamide Synthesis for Fundamental Research on Solvent Extraction Systems

ABSTRACT

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.

KEYWORDS:

• Malonamide
• deuteration
• solvent extraction
• neutron scattering

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/07366299.2023.2166351

Acknowledgments

This work was supported in part by the Ministry of Education, Culture, Sports, Science and Technology, Japan (Grants-in-Aid for Young Scientists (B), 2021-2023, No. 21K17911; Grant-in-Aid for Scientific Research B, 2022–2025, No. 22H02010; Grant-in-Aid for Research Activity Start-up, 2022−2024, No. 22K20487; and the Japan-France bilateral cooperative program, Sakura Project, No. JPJSBP120223211). We gratefully acknowledge the Center for Instrumental Analysis at Ibaraki University for providing the opportunity to use the NMR instrument. We thank Dr. Mitsuhiro Honda and Ms. Yui Kaneta for assisting with X-ray fluorescence measurements. Direct deuteration reactions were conducted at the User Experiment Preparation LabIII (CROSS). ¹H, ²H, ¹³C NMR, and ESI–MS spectroscopy experiments were conducted at the Deuteration Laboratory in J-PARC MLF. Access to the experiment at the SANS-J (C3-2) was provided by JRR-3 with the approval of the Japan Atomic Energy Agency (JAEA; Proposal no. 2022-D568).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the JSPS [21K17911,22H02010,22K20487,JPJSBP120223211]; Ministère des Affaires Étrangères [JPJSBP120223211].