Chemistry Reference
In-Depth Information
amounts of Ln(III) in the An(III) product solution were lower than 2.5
wt%.
2. Second, as a “solvent recycle” process, which ran for 54 hours without
solvent clean-up to treat 3.85 L of a DIAMEX An(III) + Ln(III) product.
This second hot test, which generated 6.5 L of Am(III) + Cm(III) product,
revealed partial degradation of
i
iPr-BTP, probably because of alpha/gamma
radiolysis reflected by a 40% decrease in the solvent-extraction performance
observed after two cycles (
207
).
Attempts to improve the chemical stability of BTP ligands by fully substituting
the carbon atoms on the α position of the triazine rings led the organic chemists of
the University of Reading to design and synthesize Bis-Annulated-Triazine-Pyridines
(BATP, Figure 3.18), such as 2,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]
triazin-3-yl) pyridine (CyMe
4
-BTP) or 2,6-bis(9,9,10,10-tetramethyl-9,10-dihydro-
1,2,4-triaza-anthracen-3-yl) pyridine (BzCyMe
4
-BTP), in which the labile α-benzylic
hydrogens have been replaced by methyl groups (
210
). The hydrolytic stability of
CyMe
4
-BTP is as good as that of
i
iPr-BTP. It was demonstrated that the nature of the
organic diluent (aliphatic, aromatic, nitro-aromatic) also influences the stability of the
BTP ligands, especially those presenting radical-scavenging properties (
211, 212
).
The distribution ratio of Am(III) is much higher for CyMe
4
-BTP than for
i
Pr-BTP
when mixed with DMDOHEMA in
n
-octanol, and the observed An(III)/Ln(III)
selectivity is outstanding for an N-soft-donor ligand: SF
Am/Eu
> 1500 at equilibrium
(
207
). Nevertheless, stripping becomes problematic, and further investigations and
optimizations are still required before this system can be applied to countercurrent
test implementation.
Bis-Triazinyl-BiPyridines
. A new class of tetradentate N-donor polyazine ligands
was designed at the University of Reading during the European collaborative proj-
ect EUROPART of the EURATOM 6th Framework Program: the Bis-Triazinyl-
BiPyridines (BTBPs) (
207
), consisting of two 5,6-dialkyl-[1,2,4]-triazinyl groups
linked by a central dipyridyl moiety (Figure 3.18). The motivation for turning triden-
date BTPs into tetradentate BTBPs was multiple:
•
Increase the solubility of the nitrogen-donor ligands in aliphatic diluents
•
Improve the An(III)/Ln(III) selectivity by increasing the denticity of the
ligand
Improve the hydrolytic/radiolytic stability of the BTPs
•
The extraction properties of the BTBPs toward trivalent lanthanides and actinides
have been intensively investigated as a function of the nature of the organic diluent
or phase-transfer catalyst and as a function of the ionic strength and acidity of the
aqueous phase (
47, 210-215
).
The stoichiometry of the extracted M(III) complexes differs from that of the
above-mentioned BTP ligands in that M:L
2
complexes (instead of M:L
3
complexes)
have been identified by various techniques (e.g., X-ray crystallography, nuclear mag-
netic resonance, electro-spray ionization mass-spectrometry, and slope analysis in
liquid-liquid extraction).
