A highly efficient solvent system containing functionalized diglycolamides and an ionic liquid for americium recovery from radioactive wastes

Three room temperature ionic liquids (RTILs), viz. C(4)mim(+)·PF(6)(-), C(6)mim(+)·PF(6)(-) and C(8)mim(+)·PF(6)(-), were evaluated as diluents for the extraction of Am(III) by N,N,N',N'-tetraoctyl diglycolamide (TODGA). At 3 M HNO(3), the D(Am)-values by 0.01 M TODGA were found to be 102, 34 and 74 for C(4)mim(+)·PF(6)(-), C(6)mim(+)·PF(6)(-) and C(8)mim(+)·PF(6)(-), respectively. The extraction of Am(III) decreased with increasing feed acidity for all three diluents, indicating an ion exchange mechanism for the extraction. The stoichiometry of the extracted species suggested that two TODGA molecules were associated with Am(III) during the extraction for all three RTILs and the conditional extraction constants have been determined. The D(M)-values for different metal ions followed the order: 75 (Am(III)) > 30.7 (Pu(IV)) > 3.9 (Np(IV)) > 1.19 (Pu(VI)) > 0.52 (U(VI)) > 0.12 (Cs(I)) > 0.024 (Sr(II)). The distribution behaviour of Am(III) was also studied with a recently synthesized calix[4]arene-4DGA (C4DGA) extractant dissolved in C(8)mim(+)·PF(6)(-). Using this extractant diluent combination, the D(Am)-value was 194 at 3 M HNO(3) using 5 × 10(-5) M C4DGA, suggesting a very high distribution coefficient at very low extractant concentrations. The stoichiometry of the extracted species containing Am was found to be 1:2 (M:L) in C(8)mim(+)·PF(6)(-). The thermodynamics of the extraction was also studied for both extractants in C(8)mim(+)·PF(6)(-). The use of RTILs gives rise to significantly improved extraction properties than the commonly used n-dodecane and an unusual increase in separation factor values was seen for the first time which can lead to selective separation of Am from wastes containing a mixture of U, Pu and Am.     

Product distribution of peroxynitrite decay as a function of pH, temperature, and concentration.

The decay of peroxynitrite [O=NOO(-), oxoperoxonitrate(1-)] was examined as a function of concentration (0.050-2.5 mM), temperature (5-45 degrees C), and pH (2.2-10.0). Below 5 degrees C and pH 7, little amounts of the decomposition products nitrite and dioxygen are formed, even when the peroxynitrite concentration is high (2.5 mM). Instead, approximately > or =90% isomerizes to nitrate. At higher pH, decomposition increases at the expense of isomerization, up to nearly 80% at pH 10.0 at 5 degrees C and 90% at 45 degrees C. Much less nitrite and dioxygen per peroxynitrite are formed when the peroxynitrite concentration is lower; at 50 microM and pH 10.2, < or =40% decomposes. In contrast to two other reports (Pfeiffer, S.; Gorren, A. C. F.; Schmidt, K.; Werner, E. R.; Hansert, B.; Bohle, D. S.; Mayer, B. J. Biol. Chem. 1997, 272, 3465-3470, and Coddington, J. W.; Hurst, J. K.; Lymar, S. V. J. Am. Chem. Soc. 1999, 121, 2438-2443), we find that the extent of decomposition is dependent on the peroxynitrite concentration.     

Highly Efficient Diglycolamide‐Based Task‐Specific Ionic Liquids: Synthesis,Unusual Extraction Behaviour,Irradiation, and Fluorescence Studies

Two new diglycolamide‐based task‐specific ionic liquids (DGA? TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA? TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am³⁺, and even higher extraction of the lanthanide ion, Eu³⁺ (about 5–10 fold). Dilution of the DGA? TSILs in an ionic liquid, C₄mim⁺ ? NTf₂^?, afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO₃^? anion, along with the participation of two DGA? TSIL molecules. Time‐resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner‐sphere water molecule in the Eu^III? DGA? TSIL complexes in the presence and absence of C₄mim⁺ ? NTf₂^? as the diluent. The very high radiolytic stability of DGA? TSIL 6 makes it one of the most‐efficient solvent systems for the extraction of actinides under acidic feed conditions.     

Water increases rates of epoxidation by Mn(III)porphyrins/imidazole/IO4(-) in CH2Cl2. Analogy with peroxidase and chlorite dismutase

Manganese(III)-meso-tetraphenylporphyrin [Mn(TPP)] and manganese(III)-meso-tetrakis(pentafluorophenyl)porphyrin [Mn(TPFPP)] catalyse the epoxidation of cyclooctene by IO(4)(-) in the presence of excess imidazoles, in both dry CH(2)Cl(2) and CH(2)Cl(2) saturated with H(2)O. The reaction rates of the electron deficient Mn(TPFPP) are a factor 24 less than those of Mn(TPP); however, the former increases 15-30 times in the presence of water, while those of Mn(TPP) do so by a factor of 2-3. The most striking catalytic enhancement caused by the addition of water was observed with 2-methylimidazole and Mn(TPFPP). As deprotonation of imidazoles may play a significant role in the presence of water, we found that manganese(III)-meso-tetrakis(phenyl-4-sulfonato)porphyrin [Mn(TPPS)] decreases the NH proton pK(a) of axially coordinated imidazole from 14.2 to 9.5. We conclude that the imidazole ligand is partially deprotonated in the presence of water. The latter enables the solvation of imidazolium ions that are formed simultaneously. The imidazolate form of the co-catalyst is a much stronger donor than the imidazole itself, providing electron density to Mn(III) and thus promoting oxygen transfer. The failure of N-methylimidazole to increase the reaction rates upon addition of water supports this hypothesis. A functionally related deprotonation has been shown to occur in horseradish peroxidase (J. S. de Ropp, V. Thanabal, G. N. La Mar, J. Am. Chem. Soc. 1985, 107, 8270-8272) and in chlorite dismutase (B. R. Goblirsch, B. R. Streit, J. L. Dubois, C. M. Wilmot, J. Biol. Inorg. Chem. 2010, 15, 879-888). Mn(III)porphyrins in combination with imidazoles and water constitute a functional biomimetic model of peroxidases.     

Sequential isomerization and ring-closing metathesis: masked styryl and vinyloxyaryl groups for the synthesis of benzo-fused heterocycles

The use of an aryl allyl ether and an arylallyl group as masked vinyl ether and 1-propenylphenyl groups for ring-closing metathesis (RCM) leading to the synthesis of benzo-fused heterocycles was demonstrated by using a ruthenium-mediated isomerization followed by a ruthenium-mediated RCM reaction. This resulted in the syntheses of a variety of products including two substituted benzo[1,4]dioxins, a naphtho[2,3-b][1,4]dioxin, a 2H-chromene and a benzo[b]furan.     

Kinetics evidence for a complex between peroxynitrous acid and titanium(IV)

The reaction between TiO(2+) and ONOOH in 0.9 M H(2)SO(4) provides evidence for direct formation, previously unobserved, of a HOONO-metal complex. The reaction proceeds via formation of an end-on complex (k = 3.0 x 10(2) M(-1) s(-1)) that rearranges to form a side-on complex (k approximately equal to 20 s(-1)). With ONOOH in excess, this rearrangement proceeds more slowly (k approximately equal to 0.1 s(-1)), probably because multiple hydrogen oxoperoxonitrate molecules form end-on complexes with oxotitanium(IV) and hinder rearrangement to the side-on complex. The absorption spectrum of the final product is that of TiO(2)(2+). Presumably, during the rearrangement or later, NO+ is lost.