A. Pandey, S. Hashmi, V. Kathirvelu et al.
Journal of Molecular Liquids 323 (2021) 114944
enhance the extraction efficiency many folds than the conventional sol-
vents [16–18]. Application of ionic liquids has also induced the research
domain of chemically embedding functionalities on ionic liquid moie-
ties for task-specific applications to improve selectivity [19–21].
It is believed that the most unique characteristics of ionic liquid re-
main in their tunability. It was reported that a small modification in ei-
ther cationic or anionic part of ionic liquids can lead to a drastic change
in their physico-chemical properties. Hence, by introducing such modi-
fication, the desired property of ionic liquid can be tuned according to
the applications [22–24]. This fact led ionic liquid to be considered as
1-octyl-3-methylimidazolium triflate, 1-butyl-3-methylimidazolium bro-
mide, 1-hexyl-3-methylimidazolium bromide, and 1-octyl-3-
methylimidazolium bromide were procured from TCI Chemical Pvt. Ltd.,
India. Fig. 1 shows the structure of substitute imidazolium with the differ-
ent anionic part. Nitric acid used in the present investigation is of
Suprapure grade and was procured from Sigma Aldrich. The other analyt-
ical grade reagent like NaNO
also procured from Sigma Aldrich. Quartz double distilled (QDD) water
was used throughout the experiment. U and ThO powder with more
3 2 3
, N CO , n-dodecane and oxalic acid, were
3
O
8
2
than 99% purity were used to obtain the stock solution of U and Th respec-
tively. The purity of these powders was ascertained by the Round Robin
test between different laboratories in Department of Atomic Energy,
‘designer solvent’. Therefore, it is very interesting to investigate the ef-
fect of structural modification of ionic liquid on the extraction proper-
ties, speciation of the systems of interest.
3 8 3
India. U O powder was dissolved in Conc. HNO and after repeated evap-
U is the key metals for sustaining nuclear energy, which is one of the
prominent alternative environmentally benign resources to meet the
ever-increasing energy demand worldwide [25]. Thorium is the fertile
material, to be used at the third stage of the Indian nuclear energy pro-
gramme [26,27]. Several phosphorous based ligand functionalities in-
volving phosphate, phosphonate, phosphinic acid, phosphonic acid,
phosphine oxide showed highly efficient extraction of uranyl ion as
well as thorium ion [28–30]. However, due to the presence of P, these
ligands were not completely incinerable. In view of that, there was al-
ways a hunt to find out efficient and selective ligand functionalities.
The amide derivatives of isophthalic acid and dipicolinic acid find
numerous applications in the field of coordination, supramolecular
and analytical chemistry with broad application in health, biology, and
the environment. These groups have shown utility in the coordination
chemistry of transition metals [31], lanthanides [32] and have been
extended to the extraction of radionuclides [33–35]. Recently, an
Isophthalamide derivative has been studied in pyridinium-based ionic
oration, the final uranium stock solution was made in 1 M HNO
3
and hence
most of the U exists as UO2
+
. However, making Th stock solution using
2
ThO
2
powder was not very easy. A catalytic amount of HF was essential
−
for that. The stock solution of Th should be free of F ion and that was
achieved by repeated evaporation. Finally, the Th stock solution was also
3
prepared in 1 M HNO . The estimation of U and Th was carried out by
using Energy Dispersive X-ray Fluorescence (EDXRF) Spectroscopy. The
EDXRF based estimation was carried out using the spectrometer procured
from Xenemetrix (Model: EX3600SDD) [47].
2.2. Synthesis of ligands
2.2.1. 5-bromo-N1,N3-bis(1-methyl-1H-pyrazol-3-yl)isophthalamide (L)
A suspension of 5-bromoisophthalic acid (0.490 g, 2 mmol) and thi-
onyl chloride (2.90 ml, 40 mmol) was refluxed under nitrogen atmo-
sphere for 16 h, formed a clear colourless solution. The resulting
solution was concentrated in vacuum to remove the excess of thionyl
chloride yielded a colourless viscous liquid, 5-Bromoisophthaloyl
dichloride. This acid chloride was then dissolved in dry dichlorometh-
ane (10 ml) and cooled to 0 °C. A solution of 3-amino-1-methylpyrazole
(0.35 ml, 4.0 mmol) and triethylamine (1.1 ml, 8.0 mmol) in dry dichlo-
romethane (5 ml) was added drop wise. The reaction mixture was
stirred for 16 h at room temperature under nitrogen atmosphere [48].
The reaction mixture was then dried over the vacuum. The residue
was dissolved in dichloromethane and washed with aqueous ammo-
nium chloride solution followed by water. The organic phase was
liquid for highly effective and selective separation of UO2
+
and Th
4+
2
[36]. The isophthalamide group is one of the major anion binding motifs
in the supramolecular chemist's inventory. Since this motif was first
demonstrated by Crabtree and co-workers to bind halides [37], the
hydrogen bond donating properties of these systems have been used
in many applications, including anion sensing and transport [38–40].
Isophthalamide and dipicolinamide groups also play a significant
role in chemosensing, molecular recognition, and detection of
various analytes [41]. Secondary amide containing ligands like N,
N-dihexyloctanamide was reported to be an environmentally benign ef-
ficient alternative to the workhorse ligand tri-n-butyl phosphate for the
2 4
dried over anhydrous Na SO and concentrated to dryness yielded com-
pound (L). The compound was purified by silica gel column chromatog-
raphy with petroleum ether and ethyl acetate (80 to 90%) mixture as
2
+
4+
extraction of UO
2
and Th [42–44]. Diglycolamides, malonamides,
methyl-octyl phosphine oxides were other ligand functionalities that
eluent, afforded 0.643 g (80%) of white solid (L); R
f
= 0.35, TLC (eluent:
petroleum ether/ethyl acetate 20:80 v/v); H NMR (300 MHz, CDCl ) δ:
10.05 (s, 2H, 2 × NH amide), 8.50 (s, 1H, ArH), 8.38 (s, 2H, 2 × ArH), 7.32
(s, 2H, 2 × Pyraz.CH), 7.28 (CDCl ), 6.88 (s, 2H, 2 × Pyraz.CH), 3.84 (s,
); CNMR(75.47 MHz, CDCl ) δ: 162.46, 147.18,
2
+
4+
1
could be used for UO
2
and Th extraction. However, trivalent lantha-
3
nides and actinides were also getting co-extracted along with hexa and
tetravalent actinides [45,46]. In view of such potential of amide func-
tionalities, the novel ligand: 5-bromo-N1,N3-bis(1-methyl-1H-
pyrazol-3-yl)isophthalamide in combination with methylimidazolium
based ionic liquids with structural modification was utilized for the effi-
cient extraction of U and Th. The investigation involves an understand-
ing of extraction kinetics, complex speciation, mechanism tunning,
stripping and radiation stability of the solvent systems.
3
13
6H, 2 × Pyraz.CH
3
3
−
1
135.69, 134.76, 131.22, 123.94, 122.96, 97.79, 38.55; FTIR (KBr, cm ):
3371–3300 (s, N\\H str. amide), 3080(C\\H str. aromatic), 2933(s,
C\\H str. alkane), 1678(s, C_O str. amide), 1591–1411(C_C str. aro-
matic), 1294(C\\N str. aromatic amine), 893–754 (C\\H bending aro-
+
matic), 673(C\\Br str.); MS (LC-MS) m/z (% rel.): 403 [M + H ]
+
(
4.49), 405 (3.49), 425 [M
+
Na
]
(9.99), 427 (7.60), 827
+
2
. Experimental
.1. Materials and methods
-Bromoisophthalic Acid, 3-amino-1-methylpyrazole, and triethy-
[2 M + Na ] (49.91), 829 (100), 831 (55.54). Anal. Calcd for
16 15 6 2
C H N O
Br: С 47.6; Н 3.7; N 20.84. Found: С 47.9; Н 3.7; N 20.79
2
(Scheme 1 and Fig. 2).
5
2.2.2. Extraction
lamine were purchased from TCI Chemicals. Dichloromethane and thionyl
chloride were purchased from SRL Chemicals. The solvents were freshly
distilled before use. NMR spectra were recorded on a Bruker Avance
The extraction processes carried out in the present investigation
mainly subdivided into the following areas.
1
2
3
4
5
. Extraction profile establishment
. Metal-ligand stoichiometry determination
. Extraction kinetics
. Participation of nitrate ion in complexation
. Participation of imidazolium ion
1
13
4
300 MHz spectrometer at 300.13( H), 75.47 MHz( C) with SiMe as inter-
nal references. The mass spectrum was collected on LC-MS (Shimadzu)
instrument. The IR spectrum was recorded on IRAffinity-1, Fourier Trans-
form Infrared Spectrophotometer (Shimadzu). The ionic liquid, 1-butyl-
3-methylimidazolium triflate, 1-hexyl-3-methylimidazolium triflate,
2