Structural Characterization of Some Acylisoxazolone Extractants

From IR, UV, ³¹P, ¹H, and ¹³C NMR spectroscopic data, it is shown that the three 3-phenyl-4-acyl-isoxazol-5-ones, HPXI (HPBI, HPTI, and HPtbBI with acyl-, benzoyl-, toluoyl-, and para-(tert-butyl)benzoyl-, respectively), promising extractants of actinides, appear under the same major tautomeric forms, both in the solid and in solutions in various solvents: the diketo-enamine form in methanol, a -ketoenolic form in the solid, and in chloroform, benzene, and toluene. The radiocrystallographic structures of HPTI and HPtbBI have been determined. They appear as 3-phenyl-4-(-hydroxybenzylidene)isoxazol-5-ones, forming intramolecular chelates through H-bonds. -Aryl interactions might influence the relative positions of the -ketoenolic oxygen atoms and, hence, the bite angle and the cone angle of these ligands. Spectroscopic data give evidence of strong TOPO–HPXI interactions (TOPO: tri-n-octylphosphine oxide) in toluene, of the same order of magnitude for the three acylisoxazolones, in the order: HPBI > HPTI > HPtbBI.