Studies of the Liquid-Liquid Partition Systems. VIII. Stabilities and Extractabilities of Copper(II) and Zinc(II) Complexes with Acetylacetone, Trifluoroacetylacetone, and Hexafluoroacetylacetone in Aqueous Sodium Perchlorate Solution-Carbon Tetrachloride Systems
Abstract:The distribution of copper(II) and zinc(II) chelates with three β-diketones, acetylacetone (AA), trifluoroacetylacetone (TFA), and hexafluoroacetylacetone (HFA) between carbon tetrachloride and aqueous sodium perchlorate solutions at 0.1m, 1m, and 3m has been determined at 25°C as a function of the concentration of the dissociated chelate anions. The stability constants for the metal chelates in the aqueous phase and the two phasedistribution constants for the uncharged complexes have been determined by a grap… Show more
“…Furthermore, the model successfully predicted the inability of acetylacetone to extract copper in a single equilibrium stage even when used in large excess. For model calculations, the equilibrium constant data were obtained from Sekine and Ihara (8), and a model run was made for 35 °C and 96 atm. The computer model yielded an extraction efficiency of less than 1%, consistent with the observed phenomena.…”
Section: Discussionmentioning
confidence: 99%
“…System selection was based on the availability of the input data necessary to model the system behavior. Solvent extraction of copper from aqueous solutions using carbon tetrachloride as a solvent was investigated in detail by Sekine and Ihara (8). The authors reported values of copper complex stability constants for acetylacetone and hexafluoroacetylacetone.…”
The primary goal of this research was to investigate the
feasibility of removing heavy metals from wastewater by
chelation in supercritical carbon dioxide. Copper was
used
as the model contaminant. Extraction efficiency was
determined as a function of temperature, pressure, initial moles
of chelating agent, and initial moles of copper in a
300-cm3
autoclave. Results indicated that 60% removal of
copper
can be achieved in a single equilibrium stage with an
initial copper concentration of 100 ppm and
hexafluoroacetylacetone (HFA), present in excess, as the chelating
agent.
Experimental extraction efficiencies ranged from 14 to
60%
and increased with increasing initial chelate
concentration
and CO2 density and with decreasing initial
copper
concentration. A thermodynamic model based on
combined
reaction and phase equilibria was developed for the
prediction of extraction efficiencies. Five
aqueous-phase
reactions and four phase equilibrium relations were
considered in the development of the model.
Equilibrium
constants and phase distribution coefficients were either
drawn from the available literature or measured. The
distribution coefficient of the copper−chelate complex
was estimated as the ratio of the solubility of the
complex
in the supercritical phase to its solubility in the
aqueous
phase. The model successfully predicted the effects of
tem
perature, pressure, and initial amounts of chelating agent
and metal contaminant on extraction efficiencies without
the use of any adjustable parameters.
“…Furthermore, the model successfully predicted the inability of acetylacetone to extract copper in a single equilibrium stage even when used in large excess. For model calculations, the equilibrium constant data were obtained from Sekine and Ihara (8), and a model run was made for 35 °C and 96 atm. The computer model yielded an extraction efficiency of less than 1%, consistent with the observed phenomena.…”
Section: Discussionmentioning
confidence: 99%
“…System selection was based on the availability of the input data necessary to model the system behavior. Solvent extraction of copper from aqueous solutions using carbon tetrachloride as a solvent was investigated in detail by Sekine and Ihara (8). The authors reported values of copper complex stability constants for acetylacetone and hexafluoroacetylacetone.…”
The primary goal of this research was to investigate the
feasibility of removing heavy metals from wastewater by
chelation in supercritical carbon dioxide. Copper was
used
as the model contaminant. Extraction efficiency was
determined as a function of temperature, pressure, initial moles
of chelating agent, and initial moles of copper in a
300-cm3
autoclave. Results indicated that 60% removal of
copper
can be achieved in a single equilibrium stage with an
initial copper concentration of 100 ppm and
hexafluoroacetylacetone (HFA), present in excess, as the chelating
agent.
Experimental extraction efficiencies ranged from 14 to
60%
and increased with increasing initial chelate
concentration
and CO2 density and with decreasing initial
copper
concentration. A thermodynamic model based on
combined
reaction and phase equilibria was developed for the
prediction of extraction efficiencies. Five
aqueous-phase
reactions and four phase equilibrium relations were
considered in the development of the model.
Equilibrium
constants and phase distribution coefficients were either
drawn from the available literature or measured. The
distribution coefficient of the copper−chelate complex
was estimated as the ratio of the solubility of the
complex
in the supercritical phase to its solubility in the
aqueous
phase. The model successfully predicted the effects of
tem
perature, pressure, and initial amounts of chelating agent
and metal contaminant on extraction efficiencies without
the use of any adjustable parameters.
“…The nucleophilic attack of the pyrrolenine nitrogen is more advantageous for the CuL 2 complex with the more fluorinated L, because more positive charge on the Cu(II) ion is expected for CuL 2 with the less negative O atoms, which is the case of the CuL 2 complex with more fluorinated L. The electrostatic repulsion between the peripheral C 6 F 5 groups of H 2 tpfpp and the terminal substituents of L contributes to the faster Cu(II) ion incorporation for the CuL 2 complex, since the dissociation of the L - ligand from the Cu(II) center can be assisted by such repulsion. Furthermore, because the required energy to dissociate L - from the Cu(II) ion should be smaller for the CuL 2 complex with the more fluorinated L, as indicated by the stability constants for the formation of CuL 2 in aqueous solution, the activation process is considered to be much easier for the CuL 2 complex with the more fluorinated L. According to the above discussions, an expected feature of the transition state is depicted in Scheme . 2 …”
The copper(II) ion incorporation reactions into 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H2tpfpp) to
form the Cu(tpfpp) complex have been kinetically investigated with bis(β-diketonato)copper(II) complexes
(CuL2) such as bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)copper(II) (Cu(hfac)2), bis(1,1,1-trifluoropentane-2,4-dionato)copper(II) (Cu(tfac)2), bis(2,2,6,6-tetramethylheptane-3,5-dionato)copper(II) (Cu(hmac)2), and bis(pentane-2,4-dionato)copper(II) (Cu(acac)2) in supercritical carbon dioxide (scCO2) using a previously developed
stopped-flow instrument and spectrophotometric cell. Saturation dependence was observed for the conditional
first-order rate constants (k
obs) as a function of the mole fraction of excess CuL2 (x
Cu): k
obs = k
2
K
1
x
Cu/(1 +
K
1
x
Cu), where K
1 is the preequilibrium constant for the fast outer sphere association between H2tpfpp and
CuL2 and k
2 is the first-order rate constant for the rate-determining copper(II) ion incorporation into the
porphyrin core. Under constant temperature (333 K) and pressure (20.0 MPa), the K
1 values are in the order
of Cu(hfac)2 < Cu(tfac)2 < Cu(hmac)2 < Cu(acac)2; this trend has been interpreted by the differences in the
solvation energy of the CuL2 complexes in scCO2 and in the electrostatic repulsion between H2tpfpp and
CuL2 anticipated in the outer sphere association complex. On the other hand, the k
2 values are in the following
order: Cu(hfac)2 > Cu(tfac)2 > Cu(hmac)2 > Cu(acac)2. This order may be explained by the affinity of
CuL2 for the nucleophile of the pyrrolenine nitrogen, the easiness of dissociation of the β-diketonate ligand,
and the electrostatic repulsion between H2tpfpp and CuL2. The thermodynamic and kinetic parameters in
scCO2 were obtained as follows: K
1 = (5.2 ± 0.1) × 104 (333 K, 20.0 MPa), ΔH
1
° = 76 ± 2 kJ mol-1 (20.0
MPa), ΔS
1
° = (3.2 ± 0.7) × 102 J mol-1 K-1 (20.0 MPa), ΔV
1
° = (7.9 ± 0.6) × 102 cm3 mol-1 (333 K), k
2
= (2.7 ± 0.3) × 10-4 s-1 (333 K, 20.0 MPa), Δ‡
H
2
° = −49 ± 9 kJ mol-1 (20.0 MPa), Δ‡
S
2
° =
(−4.6 ± 0.3) × 102 J mol-1 K-1 (20.0 MPa), and Δ‡
V
2
° = (−4.4 ± 0.6) × 102 cm3 mol-1 (333 K). In
addition, the reaction of H2tpfpp with Cu(hfac)2 has been studied in n-hexane in order to compare the results
in scCO2 with those in a conventional nonpolar solvent.
“…The standard enthalpies of formation of both of the chelating agents were assumed to be the same as that of acetylacetone, which was calculated by fitting the dissociation constants of acetylacetone in the temperature range 283-323 K (Liljenzin, 1969) to the van't Hoff equation. The complexation constant of Cu(TFA) 2 was obtained from Sekine and Ihara (1971). The complexation constant of Cu(FOD) 2 was treated as an adjustable parameter in the model.…”
Copper removal from aqueous solutions by chelation in supercritical carbon dioxide was investigated. The chelating agents were 1,1,1-trifluoroacetylacetone (TFA) and 2,2-dimethyl- 6,6,7,7,8,8,. Extraction efficiencies were determined for a single equilibrium stage in the temperature range 308-328 K and the pressure range 9.9-24.0 MPa and ranged from 4% to 84%. The extraction efficiencies increased with increasing the initial amount of chelating agent and with decreasing the initial copper concentration. No significant changes in extraction efficiencies were observed with temperature and pressure at a fixed initial amount of chelating agent. A thermodynamic model based on combined reaction and phase equilibria was also developed for prediction of extraction efficiencies.
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