Synthesis of symmetric dithiophosphinic acids for “minor actinide” extraction

New aromatic dithiophosphinic acid (R2PS2H; DPAH) derivatives were isolated using a synthetic pathway based on nucleophilic addition at phosphorus, which leads to regiospecific aromatic substituents on phosphorus. The synthesis improves DPAH designs that can provide insight into the differences in binding/chelation between DPAH and trivalent actinides/lanthanides. The synthesis gives good yields via isolation of the DPAH as the ammonium salt. Multinuclear NMR spectroscopy and X-ray structure determination are used for the identification of both the ammonium salt and free acid of the dithiophosphinic derivatives. The DPAH products are stable when exposed to the ambient atmospheric conditions for long periods. For instance, the bis(o-trifluoromethylphenyl) DPAH derivative showed very little degradation when contacted with water and nitric acid for prolonged periods. Furthermore, this derivative selectively extracts a trivalent actinide from a lanthanide with separation factors of ∼100 000 at low pH. Overall, these DPAH derivatives are exciting new compounds for potential application in actinide and lanthanide separations technologies.

Graphical abstractNew dithiophosphinic acid (DPAH) derivatives were synthesized using a nucleophilic addition at phosphorus. The synthesis improves DPAH designs that can provide insight to the differences between trivalent actinide and lanthanide binding/chelation. The DPAH products are stable when exposed to the atmosphere, water and nitric acid for long periods. The most important finding is that bis(o-trifluoromethylphenyl) DPAH (figure shown) selectively separates Am(III) from Eu(III) with separation factors of ∼100 000 at low pH.Figure optionsDownload full-size imageDownload as PowerPoint slide