Solvent extraction of metal ions from nitric acid solution using N,N ′-substituted malonamides. Experimental and crystallographic evidence for two mechanisms of extraction, metal complexation and ion-pair formation
作者:Gabriel Y. S. Chan、Michael G. B. Drew、Michael J. Hudson、Peter B. Iveson、Jan-Olov Liljenzin、Mats Skålberg、Lena Spjuth、Charles Madic
DOI:10.1039/a605577j
日期:——
The solvent extraction of actinides including Am
III
and
Cm
III
together with some trivalent lanthanides from nitric
acid solutions by two newly synthesized malonamides,
N,Nâ²-dimethyl-N,Nâ²
-diphenyltetradecylmalonamide (dmptdma) and
N,Nâ²-dicyclohexyl-N,Nâ²
-dimethyltetradecylmalonamide (dcmtdma) has been investigated and
compared with data for the reference malonamide,
N,Nâ²-dibutyl-N,Nâ²
-dimethyloctadecylmalonamide (dbmocma). The dependence of the extraction
on the nitric acid and malonamide concentrations together with the
probable molecular structure of the extraction species from nitric acid
solution suggests that there are two principal mechanisms of extraction.
For low nitric acid concentrations (up to 1 mol dm
-3
) a
co-ordinative mechanism dominates for the extraction of metal cations,
whereas at higher nitric acid concentrations (1â14 mol
dm
-3
) an ion-pair mechanism involving the mono- or
di-protonated malonamide and the metal anions
[M(NO
3
)
4
]
-
or
[M(NO
3
)
5
]
2-
appears to be more
important. Crystal structures show that in the protonated, unalkylated
species Hdcmma
+
(dcmma = N,Nâ²-dicyclohexyl-N
,Nâ²-dimethylmalonamide) and in the chelated
complexes [Nd(NO
3
)
3
(dcmma)
2
],
[Nd(NO
3
)
3
(H
2
O)
2
(dmpma)] and
[Yb(NO
3
)
3
(H
2
O)(dmpma)]
(dmpma = N,Nâ²-dimethyl-N
,Nâ²-diphenylmalonamide) the carbonyl oxygens lie
cis to each other suggesting that it is the cis form
which is involved in extraction. However, crystal structures of the free
unalkylated malonamides
N,Nâ²-dicyclohexyl-N,Nâ²
-diethylmalonamide and
N,Nâ²-dicyclohexyl-N,Nâ²
-diisopropylmalonamide show that the carbonyl amide groups adopt a
trans configuration in which the carbonyl oxygens are at
maximum separation. By contrast, in the crystal structure of the
diphenyl derivative dmpma the carbonyl amide groups adopt a
gauche configuration with an
OC · · · C
O torsion angle of 57.2°. Conformational analysis
confirms that the differences in these structures reflect the
differences between the lowest-energy gas-phase conformations and are
not caused by packing effects.
研究了两种新合成的丙二酰胺(N,N²-二甲基-N,N²-二苯基十四烷基丙二酰胺(dmptdma)和 N、N,N²-二甲基-N,N²-二苯基十四烷基丙二酰胺(dmptdma)和 N,N²-二环己基-N,N²-二甲基十八烷基丙二酰胺(dbmocma)进行了研究,并与参考丙二酰胺 N,N²-二丁基-N,N²-二甲基十八烷基丙二酰胺(dbmocma)的数据进行了比较。萃取率与硝酸和丙二酰胺浓度的关系以及硝酸溶液中萃取物的可能分子结构表明,萃取主要有两种机制。
在硝酸浓度较低(1 摩尔分米-3 以下)的情况下,金属阳离子的萃取主要采用协同机制,而在硝酸浓度较高(1â14 摩尔分米-3)的情况下,涉及单质子或双质子丙二酰胺和金属阴离子 [M(NO 3 ) 4 ] - 或 [M(NO 3 ) 5 ] 2 - 的离子对机制似乎更为重要。
[Nd(NO 3 ) 3 (H 2 O) 2 (dmpma)]和[Yb(NO 3 ) 3 (H 2 O) (dmpma)](dmpma = N,N²-二甲基-N,N²-二苯基丙二酰胺)的螯合物中,羰基氧原子互为顺式,表明参与萃取的是顺式。然而,游离的未烷基化丙二酰胺 N,N²-二环己基-N,N²-二乙基丙二酰胺和 N,N²-二环己基-N,N²-二异丙基丙二酰胺的晶体结构显示,羰基酰胺基团采用反式构型,其中羰基氧原子的距离最大。与此相反,在二苯基衍生物 dmpma 的晶体结构中,羰基酰胺基团采用的是 OC Â- Â- Â- C O 扭转角为 57.2°的高扭构型。构象分析证实,这些结构的差异反映了最低能量气相构象之间的差异,而不是由堆积效应引起的。