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61
CHAPTER 2. EXPERIMENTAL
2.1. Materials
N-benzoyl glycine, 3-aminoacetophenone, 4-dimethylaminobenzaldehyde,
potassium hydroxide, potassium nitrate and metal salts, MCl2.nH2O (M = Ni, Cu
and Cd) were purchased from E-Merck. The surfactants used in this study, triton
x-100 (TX-100), sodium dodecyl benzene sulphonate (SDBS) and
cetyltrimethylammonium bromide (CTAB) were from Sigma-Aldrich and used as
obtained without any purification. Acetonitrile, benzene, ethanol, ether,
carbontetrachloride, 1,4-dioxane, N, N- dimethylformamide, dimethylsulfoxide,
tetrahydrofuran and all the other chemicals used in the study were of AnalaR
grade.
All the solutions used in potentiometric titrations were prepared in double distilled
water.
2.2. Physico-Chemical Techniques
Potentiometric titrations were carried out using a digital pH-meter of Eutech
Cyberscan pH 1100 with a glass calomel electrode at three different temperatures
(290.15, 300.15 and 310.15) K. The desired temperature for the titrations was
maintained using a thermostat model (D8-G Haake Mess-Techinik). The pH meter
was standardized before each titration with standard buffer solution of pH 4.00,
7.00 and 9.00 obtained from Eutech Instruments, Singapore.
Carbon, Hydrogen and Nitrogen were microanalyzed on Perkin-Elmer model
240C Analyzer. Molar conductances of the complexes were measured on a
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Systronic Conductivitymeter 306. Magnetic susceptibility measurements were
carried out on a Magnetic Susceptibility Balance, Sherwood Scientific Cambridge,
UK while the variable temperature magnetic susceptibility was measured using
SQUID. Electron Spin Resonance spectra of Cu(II) complex at room and liquid
nitrogen temperature were obtained on a Varian E-line X band ESR Spectrometer
using DPPH as a g-marker. Electronic spectra of the complexes were taken on a
Shimadzu 2450 UV-Vis Spectrophotometer. Infrared Spectra of the ligands and
the complexes were obtained using a Shimadzu Fourier Transform Infrared
(FTIR) Spectrophotometer 8400S in KBr medium. 1H and
13C NMR Spectra were
recorded in DMSO-d6 on a Jeol AL 300 FT NMR Spectrometer. Mass Spectra
were obtained on a Jeol Sx102/Da-6000 Mass Spectrometer. The thermoanalytical
(TGA – DTA) measurements were carried out with Perkin Elmer Simultaneous
Thermal analyzer STA 6000.
2.3. Preparation and characterization of the ligands
2.3.1. Preparation of 4-dimethylamino benzylidene(N-benzoyl)glycyl
hydrazone (dabBzGH)
N-benzoyl glycine hydrazide was prepared as reported [1]. 4-dimethylamino
benzylidene (N-benzoyl)glycyl hydrazone, dabBzGH was prepared by refluxing
ethanolic solutions of N-benzoyl glycine hydrazide ( 0.02 M, 1.0 g, in 10 mL) and
4-dimethylamino benzaldehyde (0.02 M, 0.77 g, in 30 mL) for 4 hours. The light
yellow precipitate obtained on slow cooling of the reaction mixture was filtered,
washed repeatedly with ethanol, recrystallized from hot ethanol and dried at room
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temperature. dabBzGH is characterized by its melting point, elemental and
hydrazine analysis, infrared, nuclear magnetic resonance and mass spectral data.
Yield = 60 %; m. p. 210 - 213°C; M+ peak at m/e = 324 as molecular ion peak in
the mass spectrum of the compound.
Figure 2.1. Structure of dabBzGH.
Scheme I. Mass fragmentation of dabBzGH.
NN
H HO
O
N
H
H
H
N
C H 3
C H 3
N
H HO
O+H
N+NH
H
N
C H 3
C H 3
N H
+CH 2O
N
C H 3
C H 3
O+
O+
NH
m /e ( 3 2 4 )
m / e ( 1 6 2 )
- C O
m / e ( 1 6 1 )
m /e ( 1 2 0 )m /e ( 1 3 4 )
m /e ( 1 0 5 )
m /e ( 7 7 )
m /e ( 1 1 9 )
- H C N + H 2
NN
O
H H
N(CH 3)2
N
O
HH
H12
3
4
1'2'
3'
4'
5'
6'
Figure 2.
Characterization of dabBzGH
Elemental and hydrazine analysis
66.96 (66.60); H, 6.20 (6.17); N, 16.97
IR (v, cm-1
). 1676 (amide
moiety, 1637 (amide I), 1529
1614 (CN), 952 (NN).
Figure 2.
Figure 2.2. Mass Spectrum of dabBzGH.
dabBzGH
hydrazine analysis: Found % (calcd %) for C18H24
(6.17); N, 16.97 (17.28); N2H4, 9.90 (9.80).
(amide I), 1554 (amide II), and 1471 (amide III) of hydrazidic
, 1529 (amide II), 1313 (amide III) of benzamide moiety,
Figure 2.3. IR spectrum of dabBzGH.
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24N4O2. C,
of hydrazidic
of benzamide moiety,
1H NMR (dmso-d6), δδδδ (ppm):
7.25 – 7.74 (9H, multiplets, ring protons), 8.66, 8.47 (H, triplets, C
11.03 (H, singlet,-NNHCO).
Figure 2.
13C NMR (dmso-d6), ppm:
152.31 (12C, 8 singlets, ring carbons), 148.41 (
C6H5CONH-), 170.63 (singlet,
Figure 2.5
(ppm): 2.70 (3H, singlet, CH3), 7.90 (H, singlet,
7.74 (9H, multiplets, ring protons), 8.66, 8.47 (H, triplets, C6H5
NNHCO).
Figure 2.4. 1H NMR spectrum of dabBzGH.
), ppm: 40.07 (singlet, -CH3), 42.88 (singlet, -CH2), 112.63
152.31 (12C, 8 singlets, ring carbons), 148.41 (-NCH-), 167.48 (doublet,
170.63 (singlet, -NNHCO).
Figure 2.5. 13
C NMR spectrum of dabBzGH.
NN
O
H H
N(CH3)2
N
O
HH
H12
3
4
1'2'
3'
4'
5'
6'
65
), 7.90 (H, singlet, -NCH),
5CONH-),
), 112.63 –
), 167.48 (doublet,
66
2.3.2. Preparation of N-(2-2-[1-(3-aminophenyl)ethylidene]hydrazino-2-
oxoethyl) benzamide (aehb)
N-(2-2-[1-(3-aminophenyl)ethylidene]hydrazino-2-oxoethyl)benzamide, aehb
was prepared by refluxing ethanolic solutions of N-benzoyl glycine hydrazide
(0.02 M, 1.0 g in 30 mL) and 3-aminoacetophenone (0.02 M, 0.7 g in 10 mL) for
4 hours. The white precipitate obtained on slow cooling of the reaction mixture
was filtered and washed repeatedly with ethanol. It was then recrystallized from
hot ethanol and dried at room temperature. aehb is then characterized based on its
melting point, elemental and hydrazine analysis, infrared, nuclear magnetic
resonance and mass spectral data.
yield = 60 %; mp 213-215°C; M+ peak at 311 as the base peak in the mass
spectrum of the ligand.
Figure 2.6. Structure of aehb.
NN
O
H CH 3
N
O
HH NH 2
H
3'
5'
6' 4'
1'2'
12
3
4
Figure 2.7.
Scheme 2.
O
m /e ( 1 6 2 )
- C O
m /e ( 1 3 4 )
m /e ( 1 0 5 )
m /e ( 7 7 )
- H C N + H 2
O
N
HO
Figure 2.7. Mass Spectrum of aehb.
Scheme 2. Mass fragmentation of aehb.
N+NH
C H 3
N H
+CH 2
O+
O+
NH
m / e ( 3 1 0 )
m /e ( 1 6 2 )
- C O
m /e ( 1 4 8 )
m /e ( 1 1 9 )
NN
H H
O
NH
H
C H 3N H 2
H
O+H
m /e ( 9 3 )
67
N H 2
N H 2
68
Characterization of aehb
Elemental and hydrazine analysis: Found % (calcd %) for C17H18N4O2. C,
65.60 (65.80); H, 5.80 (5.80); N, 17.89 (18.06); N2H4, 10.40 (10.32).
IR (v, cm-1
). 1688 (amide I), 1577 (amide II), 1329 (amide III) of hydrazidic
moiety, 1634 (amide I), 1552 (amide II), 1311 (amide III) of benzamide moiety,
1597 (CN), 995 (NN).
Figure 2.8. IR Spectrum of aehb.
45060075090010501200135015001650180019502400270030003300360039001/cm
-20
-10
0
10
20
30
40
50
60
70
80
90
100
%T
3338.89
3188.44
3082.35
1687.77
1633.76
1597.11
1577.82
1552.75
1489.10
1456.30
1415.80 1
329.00
1271.13
1184.33
1124.54
995.30
910.43
887.28
837.13
632.67
597.95
532.37
509.22
462.93
420.50
P5
1H NMR (δ). 10.74, 10.92 (d, N
CH3), 4.77 (s, CH2), 5.44 (s, N
Figure 2.
13C NMR (ppm). 171.07 (s, >
benzamide), 41.37 (s, CH
(10 s, ring carbons).
Figure 2.
10.74, 10.92 (d, NHCO), 8.98, 9.14 (d, C6H5CONH), 2.50 (d, NC
), 5.44 (s, NH2), 6.93-8.22 (m, ring protons).
Figure 2.9. 1H NMR spectrum of aehb.
171.07 (s, >CO hydrazide), 166.82, 165.93 (d, >
H2), 148.55 (s, NC), 13.57, 14.24 (d, CH3), 111.45
Figure 2.10. 13
C NMR spectrum of aehb.
NN
O
H CH3
N
O
HH NH2
H
3'
5'
6' 4'
1'2'
12
3
4
69
), 2.50 (d, NC-
166.82, 165.93 (d, >CO
), 111.45-153.0
70
2.4. Preparation of the complexes
1 g of each ligand in 20 mL ethanol (3 mmol) was mixed with ethanolic
solutions of the metal chloride (MCl2.nH2O) (3 mmol). The reaction mixture was
then refluxed. Formation of the Cu(II) complex of dabBzGH occurred after
refluxing for 4 hours in ethanolic solution. The precipitate of Cu(II) complex was
separated out after cooling and filtered, washed with ethanol and dried in air.
However, Ni(II) and Cd(II) complexes could only be isolated after refluxing for ~
20 hours. The precipitation was also to be initiated by adding ~20 mL of
acetonitrile and THF to the concentrated reaction solution. The precipitates
obtained were filtered, washed with acetonitrile and THF mixture and dried in
desicator.
2.5. Analytical Procedures
The metal contents, after destroying the organic matter with concentrated
nitric acid followed by concentrated sulphuric acid, were estimated
gravimetrically using standard literature procedures [2]. Chlorine was estimated as
AgCl. Hydrazine was determined volumetrically by KIO3 method after subjecting
the ligand/complexes to acid hydrolysis with 6 N HCl for about 4 hours. Thermal
analysis data was carried out to determine the water content.
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2.6. Potentiometric techniques
2.6.1. Preparation of reaction mixtures from the stock solutions
Preparation of stock solutions
Ligand solutions
The ligands taken for the study, dabBzGH and aehb were insoluble in water.
Therefore, the stock solutions of the ligands (0.01 M) for potentiometric titrations
were prepared by dissolving 0.324 g of dabBzGH and 0.310 g of aehb separately in
100 mL 40 % (v/v) aqueous - dioxane solution.
Metal ions solutions
Three transition metals viz, Copper, Nickel and Cadmium were chosen for the
present study. The metal solutions (0.01 M) for the potentiometric studies were
prepared by dissolving 0.4262 g of CuCl2.2H2O, 0.5943 g of NiCl2.6H2O and
0.5033 g of CdCl2.H2O in 250 mL double distilled water. All solutions were
standardized following the standard procedures [2].
Potassium hydroxide solution
A standard solution of carbonate free Potassium hydroxide solution (1.088 M)
was prepared in double distilled water and standardized with standard oxalic acid
solution (0.05 M) [2].
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Nitric acid solution
A solution of Nitric acid (0.1 M) was prepared by diluting 1.619 mL of conc.
HNO3 to 250 mL with double distilled water. The acid solution was standardized
with a standard solution of KOH [2].
Potassium nitrate solution
A solution of Potassium nitrate, KNO3 (0.5 M) was prepared by dissolving
12.638 g of solid KNO3 in 250 mL of double distilled water.
Surfactant solutions
The surfactants taken for the potentiometric study in nonionic, anionic and
cationic micellar media were TX-100, SDBS and CTAB. The stock solution of the
surfactants (50 mM) were prepared by dissolving 3.1224 g of TX-100, 4.529 mL
of SDBS and 1.8225 g of CTAB each in 100 mL double distilled water.
Preparation of reaction mixtures
The following sets of reaction mixtures were prepared.
Solution (i) : [HNO3 + KNO3]
Solution (ii) : [solution (i) + Ligand], and
Solution (iii) : [solution (ii) + MCl2. nH2O] [M = Ni, Cu, Cd]
For each set of reaction mixture, three separate solutions (iii) containing
Ni(II), Cu(II) and Cd(II) ions were prepared. The metal to ligand ratio was kept
constant at 1:2 in all the reaction mixtures. The volume of each set was made up
to 25 mL with 40 % (v/v) aqueous - dioxane solution. The ionic strength of each
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reaction mixture was maintained at 0.1 M using standard KNO3 solution as the
background electrolyte. The reaction mixtures were then titrated individually
against the standard KOH solution. All the titrations were carried out at three
different temperatures (290.15, 300.15 and 310.15) K.
For the titration in micellar media, TX-100, SDBS and CTAB were added
separately in each set of the above reaction mixtures before making up the
volume.
2.6.2. Calculation
Calculation of �� , �� and pL
The determination of stability constants of the metal complexes by pH-metric
titration method was developed by Bjerrum [3], Calvin and Wilson [4] and
modified by Irving and Rossotti [5]. The following relations were given to
calculate various parameters viz, n�H, � and pL to determine the stability constants
of the complexes.
��, the average number of protons bound to the ligand was calculated using
the relation (1).
0
0
0
)(
))((
LA
ALH
TVV
ENVVYn
+
+−−=
(1)
�, the average number of ligands attached per metal ion and pL, the free ligand
exponent were determined by the following expressions:
HMA
LM
nTVV
ENVVn
0
0
0
)(
))((
+
+−=
(2)
74
]
)log
1(
[log0
0
00
0
10V
VV
TnT
pHantiH
pL M
ML
jn
n
n
n +×
−=
∑=
=β
(3)
where Y is the number of dissociable protons present in the ligand. VL and VA are
the volumes of KOH consumed to reach a particular pH by solution (ii) and
solution (i), respectively, for the same pH reading and (VL - VA) measures the
displacement of the ligand curve with respect to the acid curve. V0 is the initial
volume of the reaction mixture (25 cm3), and E
0 and 0
LT are the resultant
concentrations of nitric acid and ligand in the reaction mixtures, respectively. 0
MT
is the metal ion concentration in solution (iii) while VM is the volume of alkali
added to solution (iii) to attain the pH reading as that of VA. βnH is the overall
protonation constant of the ligand.
Bjerrum’s half �� -value method
The proton - ligand and metal - ligand formation curves are obtained by
plotting the values of �� against pH and � against pL, respectively. The proton -
ligand and metal - ligand stability constants may then be evaluated from the
formation curves using Bjerrum’s half �-value method [3]. The proton - ligand
stability constants, log KnH are obtained from the ligand protonation curves by
taking the pH value corresponding to 0.5 �� value as the first stepwise
protonation constant, log K1H and the pH value corresponding to 1.5 �� as the
second stepwise protonation constant, log K2H and so on. The metal - ligand
stability constants, log Kn are evaluated from the metal - ligand formation curves
75
by reading out the values of pL which correspond to 0.5 � and 1.5 � as the first
and second stepwise metal - ligand stability constants, log K1 and log K2,
respectively, and so on.
Calculation of the thermodynamic parameter
The thermodynamic parameters, the overall change in free energy (∆G),
change in enthalpy (∆H) and change in entropy (∆S) were calculated by using the
temperature coefficients and Gibb’s Helmholtz equations [6].
Change in free energy (∆G) was calculated from the formation constant values
(log K) at various temperatures using the following equation:
∆G = -2.303RT log K (4)
where R (ideal gas constant) = 8.314 Jk-1
·mol-1
; K = Dissociation constant of
ligand or stability constant of the complexes; T = Absolute temperature.
Change in enthalpy (∆H) for the dissociation of ligand and complexation
process were evaluated from the slope of the plot (log K1H or log K vs 1/T) using
the graphical representation of Van’t Hoff’s equation (5) while the change in
entropy (∆S) could then be calculated using relationship (6).
∆G = ∆H – T∆S (5)
∆S = (∆H – ∆G)/T (6)
∆G values were calculated at different temperatures (290.15, 300.15 and
310.15) K where ∆H and ∆S were calculated at 300.15 K only.
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References
1. T. R. Rao, Mamta Sahay and R. C. Aggarwal. Synthesis and characterisation
of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of acetone (N-
benzoyl)glycyl hydrazone, Indian J. Chem., 24A, 79-81 (1985).
2. A. I. Vogel, A Textbook of Quantitative Inorganic Analysis, 3rd
edn., Longman:
England, (1961).
3. J. Bjerrum. Metal ammine formation in aqueous solution. P. Hasse and Son:
Copenhagen, 63 (1941).
4. M. Calvin and K. W. Wilson. Stability of chelate compounds. J. Am. Chem.
Soc., 67, 2003-2007 (1945).
5. H. M. Irving and R. J. P. Williams. The stability of transition-metal complexes.
J. Chem. Soc., 3192–3210 (1953).
6. S. Glasston. Text book of physical chemistry. 2nd
edn., New York, (1974).