Organic and Third Phase in HNO3/TBP/n-Dodecane System: No Reverse Micelles

ABSTRACTThe composition and speciation of the organic and third phases in the system HNO3/TBP (tri-n-butyl phosphate)/n-dodecane have been examined by a combination of gravimetric, Karl Fischer analysis, chemical analysis, FTIR, and 31P NMR spectroscopy, with particular emphasis on the transition from the two-phase to the three-phase region. Phase densities indicate that third-phase formation takes place for initial aqueous HNO3 concentrations above 15 M, while the results from the stoichiometric analysis imply that the organic and third phases are characterized by two distinct species, namely the mono-solvate TBP⋅HNO3 and the hemi-solvate TBP⋅2HNO3, respectively. Furthermore, the 31P NMR spectra of organic and third phase show no significant chemical differences at the phosphorus centers, suggesting that the second HNO3 molecule in the third phase is bound to HNO3 rather than TBP. The third-phase FTIR spectra reveal stronger vibrational absorption bands at 1028, 1310, 1653, and 3200–3500 cm−1, reflecting...