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Spectrophotometric and solvent extraction studies of metal complexes of some hydrazones
MICROCHEMICAL
JOURNAL
Spectrophotometric Metal
18.
85-94
and
Solvent
Complexes
of Some
G. S. VASILIKIOTIS
AND TH.
Extraction
Studies
of
Hydrazones
A. KOUIMTZIS
INTRODUCTION
In previous studies on the analytical applications of isonicotinoyl hydrazones (d-7) it was observed that these compounds form colored complexes with several cations. Some of these complexes are insoluble in aqueous solutions but soluble in various organic solvents of low dielectric constant. It was found interesting to study the extraction behavior of these metal complexes for possible analytical applications. This paper is concerned with an investigation of (a) the spectrophotometric properties in aqueous 1 : 1 (v/v) dioxane solutions and (b) the solvent extraction behavior of o-hydroxybenzaldehyde isonicotinoyl hydrazone (BIH) complexes with cobalt(II), nickel(II), zinc(II), manganese(I I) and cadmium( 1I). In addition, complex formation of ohydroxybenzaldehyde benzoyl hydrazone (BBH) with zinc(I1) and manganese(I1) is also reported. The extraction behavior of these metal complexes is interpreted in terms of the ionization of the acidic phenolic group of the ligand HL, to produce anions L-, which form with cations uncharged extractable species. EXPERIMENTAL
Hydrazones BI H and BBH were prepared according to Sah and Peoples (3) by heating together equimolar proportions of isonicotinic acid hydrazide or benzoic acid hydrazide with o-hydroxybenzaldehyde in water-ethanol solution. Their mp, after recrystallization from water-methanol mixture, were in agreement with those given in the literature (I, 3). Both hydrazides were from E. Merck A. G. and o-hydroxybenzaldehyde was from Ferak, Berlin. Organic solvents were of analytical grade from E. Merck A. G. and they were purified by standard procedures. Copyright (0 1973 by Academic Press. Inc. 411 rights of reproduction m any form reserved.
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VASILIKIOTIS
AND
KOUIMTZIS
Metal ion solutions were prepared by using nitrate salts and their concentrations were determined by conventional compleximetric methods. For buffers, the following mixtures were used: acetic acid-sodium acetate (for pH range 4.0-6.0), sodium hydroxide-sodium dihydrogen phosphate (6.0-&O), sodium hydroxide-boric acid (8.0-10.0) and sodium hydroxide-potassium hydrogen phthalate (5.0-6.0). Before their use, they were purified by extraction with the studied hydrazone solution in the corresponding organic solvent, followed by washing with several portions of the pure solvent. Apparatus Spectrophotometric measurements were made with a Zeiss, model M4QII spectrophotometer with IO-mm quartz cells. The pH values were determined with a Sargent model DR-Digital pH meter (by using a combined glass calomel electrode) standardized against 0.05 M potassium hydrogen phthalate (pH 4.00).
RESULTS
AND
DISCUSSION
Complex Formation and Absorbance Spectra Complexes were formed immediately, at room temperature, by adding an ethanolic solution of BIH or BBH to a solution of the studied cation. The absorbance was then stable for at least 90 min. Reagent BIH and its complexes with Mn(II), Ni(II), Co(II), Zn(I1) and Cd(I1) are almost insoluble in water but soluble in various organic solvents including acetone, ethanol, chloroform, 1-pentanol, I-octanol and water-dioxane mixture 1 : 1 (v/v). BIH shows acidbase indicator properties and it is colorless in slightly acidic and neutral medium but yellow in alkaline (2). The absorbance spectra of BIH and its complexes with Mn(II), Ni(II), Co(H) and Zn(I1) in aqueous dioxane 1 : 1 (v/v) are given in Fig. 1. Absorbance spectrum of BIH at pH 7.00 shows two welldefined peaks, one at 290 nm (E - 19,000) and a second at 330 nm (E - 16,000). Metal complexes of BIH have absorption maxima lying between 380 and 420 nm, except the cadmium complex where no absorption maxima up to pH 9 was defined. It can be seen that the absorbance of BIH alone is very small at the wavelength of maximum absorbance of its metal complexes. Absorption spectra of BBH and its complexes with Ni(II), Co(I1) and Cu(I1) in the same medium have been reported previously (5).
EXTRACTION
METAL
HYDRAZONE
COMPLEXES
87
FIG. 1. Absorbance spectra, in aqueous 1: 1 (v/v) dioxane, of (1) reagent BIH at pH = 7.00, (2) Mn(Il)-BIH complex at pH = 7.65, (3) Ni(II)-BIH complex at pH = 7.85, (4) Co(II)-BIH complex at pH = 8.05, and (5) Zn(II)-BIH complex at pH = 8.35. In all cases, initial concentration of BIH was 5.0 x IOm5M and initial concentration of each cation was also 5.0 x lo-” hf.
Nature of Complexes The empirical formulae of the complexes were determined by the continuous variation and mole ratio methods. It was found that all these complexes contain two molecules of reagent BlH to one metal. Work on the nature of these complexes is in progress. The results obtained suggest that BIH and BBH acts as a bidentate ligand, forming two stable six-membered chelate rings by means of the o-hydroxy group and the terminal nitrogen of the hydrazide portion. Effect of pH Standard amounts of cation and BIH solution were buffered at varying pH values and the absorbance was measured at a given wavelength for each complex. A plot of absorbance against pH values in Fig. 2 shows that the color formation is obtained at pH range 459.0. Subsequent measurements, for each complex, were carried out at pH value where the absorption showed a maximum. It was reported (5) that the copper(H)-BIH complex is formed at lower pH values, i.e., from 2.0 to 6.0. On the basis of this fact, copper
88
VASILIKIOTIS
0.01
50
6.0
AND KOUIMTZIS
7.0 PH
8.0
9.0
FIG. 2. Absorbance plotted against pH for aqueous 1: 1 (v/v) dioxane solutions of (1) Ni(II)-BIH complex at 410 nm, (2) Co(II)-BIH complex at 420 nm, (3) Mn(II)-BIH complex at 400 nm, and (4) Zn(II)-BIH at 390 nm. Initial concentration of each cation was 5.0 x IO-” M and initial concentration of BIH was 1.0 x 10m4M.
can be determined selectively at pH 4 in the presence of Zn(II), Co(H), Ni(II), Mn(I1) and Cd(I1) by using a spectrophotometric procedure. Both reagents, BBH and BIH, produce a yellow color above a pH value of 9, due to the enokation of the carbonyl group (2). Beer’s Law aad Sensitivity The absorbances of the metal complexes in aqueous 1: 1 (v/v> dioxane were found to be linearly related to the concentration of
FIG. 3. Absorbance plotted against cation concentration in aqueous 1: 1 (v/v) dioxane solutions of (I) Mn(I1) at 400 nm, (2) Ni(Il) at 410 nm, (3) Co(lI) at 420 nm, and (4) Zn(II) at 390 nm. In all cases initial concentration of BIH was 4.0 X 10m4M and the pH value was 8.40.
EXTRACTION
METAL
HYDFUZONE
TABLE MOLAR
ABSORPTIVITY
Cation Zn(II) Co(ll) Ni(ll) Mn(Il)
390 420 4 10 400
89
1
OF SOME METAL-BIH
A,,,,AW
COMPLEXES
COMPLEXES”
Molar absorptivity (I mole~km~‘) t lo-’ 2.50 2.00 1.80 I .50
-
‘l pH = 8.40
the metals over the range of 1 X lo-> M to 4.5 X lo-” M (or approximately 0.5-3 ppm) (Fig. 3). From Beer’s law, the molar absorptivity for each metal at pH 8.40 was calculated. In Table 1 these values are summarized. As a supplement to our previous work (5) BBH-Zn and BBH-Mn complexes were formed by the same procedure and their absorption spectra were also recorded at aqueous 1 : 1 (v/v) dioxane. They showed absorption maxima at 380 and 400 nm, respectively. The pH of their solutions was 8.40. Both complexes obeyed Beer’s law over the range of 1 X lo-” M to 4.5 X lo-” M (Fig. 4). The apparent molar absorptivity for the BBH-Zn complex at pH 8.40 was 2.4 X lo4 1 mole-’ cm-’ and for the BBH-Mn complex 1.35 X lo4 ‘f mole-’ cm-l in aqueous 1 : 1 (v/v) dioxane.
FIG. 4. Absorbance plotted against cation concentration in aqueous 1 : I (v/v) dioxane solutions of (1) Mn(II) at 400 nm and (2) Zn(Il) at 380 nm. In both cases initial concentration of BBH was equal to 4.0 x 10m4M and the pH value was 8.20.
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VASILIKIOTIS
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KOUIMTZIS
Solvent Extraction Studies of Metal Complexes The formation of insoluble-in-water metal complexes of BIH and BBH with Zn(II), Co(II), Ni(II), Mn(II), and Cd(I1) is probably due to the ionization of the acidic hydroxyl group of the ligand (LH). The remaining anion (L-) reacts with the metal ions and in the case of divalent cations (M2+), it forms insoluble complexes of the type ML2. These uncharged complexes are soluble in various organic solvents. The fact that the corresponding hydrazones of isonicotinic and benzoic acid hydrazides with pyridine-2-aldehyde, form soluble complexes with the same cations is most probably due to the formation of charged complexes because of the lack of an ionized hydroxyl group. As these complexes are soluble in immiscible organic solvents, a systematic study of the factors involved in solvent extraction was carried out. Chloroform (E = 4.8), 1-octanol (E = 10.3) and 1-pentanol (E = 13.9) were used as extraction solvents. The concentration of a metal complex (ML,), in the organic phase, depends, on the concentration of the ionized ligand (L-) in the aqueous phase and its concentration consequently depends on the pH of the aqueous phase. It is evident that the main factor which regulates the extraction of a cation is the pH of the aqueous phase. On the basis of this fact, the distribution ratio of cations between the aqueous and the organic phases was studied as a pH function by the following procedure. Quantities of 5 ml of 2.0 x 10V5M solution of the studied cation were placed in stoppered Erlenmeyer flasks. These solutions, presaturated with the studied solvent, were buffered at the desired pH values under a constant ionic strength of 0.1 (final volume 10 ml). A volume of IO ml of 5.0 x low4 M solution of BIH or BBH in the studied solvent, presaturated with water, was added. The mixture was shaken mechanically for 12 hr in a thermostat at 25 + 1”. After settling for 4 hr and a complete separation of the two phases, the absorbance of organic phase was measured at the wavelength for maximum absorbance against a solvent blank. At the same time the pH of the aqueous phase was measured. The distribution coefficient D of the studied cations between the two equal volume phases, was calculated from the equation D = &%mx -A) where A was the measured absorbance of the organic phase and A,,, the absorbance for a complete extraction. This value was actually the sum of absorbances measured after successive extractions of the same aqueous phase, with the studied solvent solution of BIH or BBH. In all cases the absorbance after the second extract was almost near to zero.
EXTRACTION
METAL
HYDRAZONE
COMPLEXES
91
1
a s
0
-1
6.0
zo
a0
PH Fro. 5. Distribution ratio (log D) of (1) Ni(lI) and (2) Co(U) as a pH function. In both cases initial concentration of each cation in aqueous phase was 1.O x lo-” M and initial concentration of BBH in I-octanol was 5.0 X IO+ M.
All measurements were done twice and the average values are reported. From the obtained results it is concluded that: (a) Complexes of Zn(II)-BBH, Mn(II)-BBH, and Cd(II)-BBH were not extracted with chloroform, With I-pentanol and I-octanol an improvement was noticed but generally extraction of these complexes is considered unsatisfactory. (b) Complexes of Co(H)-BBH and Ni(II)-BBH were extracted quantitatively with I-octanol as shown in Fig. 5. (c) Complexes of Zn(II)-BIH, Mn(II)-BIH, and Cd(H)-BIH are not extracted with chloroform. They are extracted with 1-pentanol. Best results were obtained with Zn(II)-BIH complex as it is shown in Fig. 6. (d) Complexes of Zn(II)-BIH, Mn(II)-BIH, Cd(H)-BIH, Co(H)-BIH, and Ni(II)-BIH were also extracted with I-octanol and results are shown in Fig. 7. By this extraction cations of Co(H), Ni(II), and Zn(I1) can be determined separately by a spectrophotometric procedure. (e) Extraction with chloroform gave fairly good results only with the Co(II)-BIH and Ni(II)-BIH complexes. It was noticed that all the studied complexes were better extracted with I-pentanol and I-octanol, i.e., with solvent of higher polarity. In the case of Co(H)-BBH complex, it was extracted with chloroform but the Co(H)-BIH complex was not. This is probably due to the more polar molecule of BIH, where a nitrogen atom is present and the complex is less soluble in a lower-polarity solvent. Conversely, the Co(H)-BIH complex is better extracted with 1-pentanol than the Co(II)-BBH complex. This is also probably the reason why the BIH
92
VASILIKIOTIS
AND KOUIMTZIS
1.0 -
a % QO-
FIG. 6. Distribution ratio (log D) of (1) Cd(II), (2) Mn(II) and (3) Zn(I1) as a pH function. Initial concentration of each cation in aqueous phase was 1.0 x 10e5M and initial concentration of BIH in I-pentanol was 5.0 X 10m4M.
complexes are better extracted with 1-pentanol than with I-octanol. The extraction of a complex may be represented by the equilibrium MY$ + ~H4ot ML(o) + aH:,,, (1) The extraction constant or the equilibrium constant of the above reac-
4.01
51)
7.0
6.0
an
I
pn
FIG. 7. Distribution ratio (log D) of (1) Cd(II), (2) Mn(II), (3) Ni(Il), (4) Zn(II), and (5) Co(I1) as a pH function. Initial concentration of each cation in aqueous phase was 1.0 x lo-” M and initial concentration of BIH in I-octanol was 5.0 x 1O-4M.
EXTRACTION
METAL
HYDRAZONE
COMPLEXES
93
tion is K, = [ML,],,[H+]~/[M”+],[LH]~
(2)
If we restrict our considerations to the pH range where the formation of intermediate complexes with the ligand may be neglected, hydrolysis products, products of reactions with other complexforming anions in the aqueous phase are also neglected and providing that only the complex ML, is extracted while all Ml’+ remains in the aqueous phase, then the ratio [ML,],/[M”+], in Eq. (2), may be considered equal to the distribution coefficient D. In this case Eq. (2) is represented as
K, = DC[H+l::/[LHl:)
or
D = K,( [LH];/[H+]$).
(3)
If a = 2 then separate plots of log D against log [LH] and against pH should be linear and of integral slope 2. The noticed deviations in the studied cases (Figs. 5-7) are probably due to complexing factors between cations and anionic buffer compounds or hydroxyl ions especially at higher pH values. Work on analytical application of the studied extraction is in progress and results will be published in due time. SUMMARY Complex formation of o-hydroxybenzaldehyde isonicotinoyl-hydrazone with Co(lt), Ni(ll), Zn(ll), Mn(ll), and Cd(I1) has been investigated. These complexes are soluble in water-dioxane 1 : 1 (v/v) solutions and they were studied spectrophotometrically. The same complexes are soluble in organic solvents and studies on their extraction with chloroform, I-pentanol and I-octanol, for possible analytical application, are reported. In addition, complex formation of o-hydroxybenzaldehyde benzoyl hydrazone with Zn(II), and Mn(l1) is also reported. REFERENCES I. Grammaticakis, P., Contribution B I’Ctude spectrale des d&i&s azotes de quelques aldChydes et &tones aromatiques. VII. Hydrazones et acidylhydrazones. Blrll. Sot. Chinz. (Frtrncr)17, 690498 (1950). 2. Katiyar, S. S., and Tandon, S. N., I-isonicotinoyl-2-salicylidene as a new chelatometric reagent. Talunta 11, 892-894 (1964). 3. *ah, P. T., and Peoples, S. A., lsonicotinoyl hydrazones as antitubercular agents and derivatives for identification of aldehydes and ketones. J. Amer. Pl~arm. Ass., Sci. Ed., 43, 5 13-524 (1954). 4. Vasilikiotis, G. S., Study on the complex formation of isonicotinoyl hydrazones with some cations and their application in the analysis. Dissertation, University of Thessaloniki. 1968. 5. Vasilikiotis, G. S., Analytical applications of isonicotinoyl hydrazones. I. A new selective reagent for mercury. Microchem. J. 13, 526-528 (1968). 6. Vasilikiotis, G. S., and Tossidis, J. A., Analytical applications of isonicotinoyl hydrazones. II. Spectrophotometric determination of aluminum with l-isonico-
94
VASILIKIOTU
AND KOUIMTZIS
tinoyl-Z-salicylidene hydrazone as chromogenic reagent. Micro&em. J. 14, 380-384 (1969). 7. Vasilikiotis, G. S., Papavasiliou, 0. Ch., and Kouimtzis Th. A., Spectrophotometric and solvent extraction studies of the complexes of copper”, cobalt” and nickel” with some hydrazones. Chimica Chronica, Proc. IVth Conf.GreekChemists, Athens 1970, p. 107.
JOURNAL
Spectrophotometric Metal
18.
85-94
and
Solvent
Complexes
of Some
G. S. VASILIKIOTIS
AND TH.
Extraction
Studies
of
Hydrazones
A. KOUIMTZIS
INTRODUCTION
In previous studies on the analytical applications of isonicotinoyl hydrazones (d-7) it was observed that these compounds form colored complexes with several cations. Some of these complexes are insoluble in aqueous solutions but soluble in various organic solvents of low dielectric constant. It was found interesting to study the extraction behavior of these metal complexes for possible analytical applications. This paper is concerned with an investigation of (a) the spectrophotometric properties in aqueous 1 : 1 (v/v) dioxane solutions and (b) the solvent extraction behavior of o-hydroxybenzaldehyde isonicotinoyl hydrazone (BIH) complexes with cobalt(II), nickel(II), zinc(II), manganese(I I) and cadmium( 1I). In addition, complex formation of ohydroxybenzaldehyde benzoyl hydrazone (BBH) with zinc(I1) and manganese(I1) is also reported. The extraction behavior of these metal complexes is interpreted in terms of the ionization of the acidic phenolic group of the ligand HL, to produce anions L-, which form with cations uncharged extractable species. EXPERIMENTAL
Hydrazones BI H and BBH were prepared according to Sah and Peoples (3) by heating together equimolar proportions of isonicotinic acid hydrazide or benzoic acid hydrazide with o-hydroxybenzaldehyde in water-ethanol solution. Their mp, after recrystallization from water-methanol mixture, were in agreement with those given in the literature (I, 3). Both hydrazides were from E. Merck A. G. and o-hydroxybenzaldehyde was from Ferak, Berlin. Organic solvents were of analytical grade from E. Merck A. G. and they were purified by standard procedures. Copyright (0 1973 by Academic Press. Inc. 411 rights of reproduction m any form reserved.
86
VASILIKIOTIS
AND
KOUIMTZIS
Metal ion solutions were prepared by using nitrate salts and their concentrations were determined by conventional compleximetric methods. For buffers, the following mixtures were used: acetic acid-sodium acetate (for pH range 4.0-6.0), sodium hydroxide-sodium dihydrogen phosphate (6.0-&O), sodium hydroxide-boric acid (8.0-10.0) and sodium hydroxide-potassium hydrogen phthalate (5.0-6.0). Before their use, they were purified by extraction with the studied hydrazone solution in the corresponding organic solvent, followed by washing with several portions of the pure solvent. Apparatus Spectrophotometric measurements were made with a Zeiss, model M4QII spectrophotometer with IO-mm quartz cells. The pH values were determined with a Sargent model DR-Digital pH meter (by using a combined glass calomel electrode) standardized against 0.05 M potassium hydrogen phthalate (pH 4.00).
RESULTS
AND
DISCUSSION
Complex Formation and Absorbance Spectra Complexes were formed immediately, at room temperature, by adding an ethanolic solution of BIH or BBH to a solution of the studied cation. The absorbance was then stable for at least 90 min. Reagent BIH and its complexes with Mn(II), Ni(II), Co(II), Zn(I1) and Cd(I1) are almost insoluble in water but soluble in various organic solvents including acetone, ethanol, chloroform, 1-pentanol, I-octanol and water-dioxane mixture 1 : 1 (v/v). BIH shows acidbase indicator properties and it is colorless in slightly acidic and neutral medium but yellow in alkaline (2). The absorbance spectra of BIH and its complexes with Mn(II), Ni(II), Co(H) and Zn(I1) in aqueous dioxane 1 : 1 (v/v) are given in Fig. 1. Absorbance spectrum of BIH at pH 7.00 shows two welldefined peaks, one at 290 nm (E - 19,000) and a second at 330 nm (E - 16,000). Metal complexes of BIH have absorption maxima lying between 380 and 420 nm, except the cadmium complex where no absorption maxima up to pH 9 was defined. It can be seen that the absorbance of BIH alone is very small at the wavelength of maximum absorbance of its metal complexes. Absorption spectra of BBH and its complexes with Ni(II), Co(I1) and Cu(I1) in the same medium have been reported previously (5).
EXTRACTION
METAL
HYDRAZONE
COMPLEXES
87
FIG. 1. Absorbance spectra, in aqueous 1: 1 (v/v) dioxane, of (1) reagent BIH at pH = 7.00, (2) Mn(Il)-BIH complex at pH = 7.65, (3) Ni(II)-BIH complex at pH = 7.85, (4) Co(II)-BIH complex at pH = 8.05, and (5) Zn(II)-BIH complex at pH = 8.35. In all cases, initial concentration of BIH was 5.0 x IOm5M and initial concentration of each cation was also 5.0 x lo-” hf.
Nature of Complexes The empirical formulae of the complexes were determined by the continuous variation and mole ratio methods. It was found that all these complexes contain two molecules of reagent BlH to one metal. Work on the nature of these complexes is in progress. The results obtained suggest that BIH and BBH acts as a bidentate ligand, forming two stable six-membered chelate rings by means of the o-hydroxy group and the terminal nitrogen of the hydrazide portion. Effect of pH Standard amounts of cation and BIH solution were buffered at varying pH values and the absorbance was measured at a given wavelength for each complex. A plot of absorbance against pH values in Fig. 2 shows that the color formation is obtained at pH range 459.0. Subsequent measurements, for each complex, were carried out at pH value where the absorption showed a maximum. It was reported (5) that the copper(H)-BIH complex is formed at lower pH values, i.e., from 2.0 to 6.0. On the basis of this fact, copper
88
VASILIKIOTIS
0.01
50
6.0
AND KOUIMTZIS
7.0 PH
8.0
9.0
FIG. 2. Absorbance plotted against pH for aqueous 1: 1 (v/v) dioxane solutions of (1) Ni(II)-BIH complex at 410 nm, (2) Co(II)-BIH complex at 420 nm, (3) Mn(II)-BIH complex at 400 nm, and (4) Zn(II)-BIH at 390 nm. Initial concentration of each cation was 5.0 x IO-” M and initial concentration of BIH was 1.0 x 10m4M.
can be determined selectively at pH 4 in the presence of Zn(II), Co(H), Ni(II), Mn(I1) and Cd(I1) by using a spectrophotometric procedure. Both reagents, BBH and BIH, produce a yellow color above a pH value of 9, due to the enokation of the carbonyl group (2). Beer’s Law aad Sensitivity The absorbances of the metal complexes in aqueous 1: 1 (v/v> dioxane were found to be linearly related to the concentration of
FIG. 3. Absorbance plotted against cation concentration in aqueous 1: 1 (v/v) dioxane solutions of (I) Mn(I1) at 400 nm, (2) Ni(Il) at 410 nm, (3) Co(lI) at 420 nm, and (4) Zn(II) at 390 nm. In all cases initial concentration of BIH was 4.0 X 10m4M and the pH value was 8.40.
EXTRACTION
METAL
HYDFUZONE
TABLE MOLAR
ABSORPTIVITY
Cation Zn(II) Co(ll) Ni(ll) Mn(Il)
390 420 4 10 400
89
1
OF SOME METAL-BIH
A,,,,AW
COMPLEXES
COMPLEXES”
Molar absorptivity (I mole~km~‘) t lo-’ 2.50 2.00 1.80 I .50
-
‘l pH = 8.40
the metals over the range of 1 X lo-> M to 4.5 X lo-” M (or approximately 0.5-3 ppm) (Fig. 3). From Beer’s law, the molar absorptivity for each metal at pH 8.40 was calculated. In Table 1 these values are summarized. As a supplement to our previous work (5) BBH-Zn and BBH-Mn complexes were formed by the same procedure and their absorption spectra were also recorded at aqueous 1 : 1 (v/v) dioxane. They showed absorption maxima at 380 and 400 nm, respectively. The pH of their solutions was 8.40. Both complexes obeyed Beer’s law over the range of 1 X lo-” M to 4.5 X lo-” M (Fig. 4). The apparent molar absorptivity for the BBH-Zn complex at pH 8.40 was 2.4 X lo4 1 mole-’ cm-’ and for the BBH-Mn complex 1.35 X lo4 ‘f mole-’ cm-l in aqueous 1 : 1 (v/v) dioxane.
FIG. 4. Absorbance plotted against cation concentration in aqueous 1 : I (v/v) dioxane solutions of (1) Mn(II) at 400 nm and (2) Zn(Il) at 380 nm. In both cases initial concentration of BBH was equal to 4.0 x 10m4M and the pH value was 8.20.
90
VASILIKIOTIS
AND
KOUIMTZIS
Solvent Extraction Studies of Metal Complexes The formation of insoluble-in-water metal complexes of BIH and BBH with Zn(II), Co(II), Ni(II), Mn(II), and Cd(I1) is probably due to the ionization of the acidic hydroxyl group of the ligand (LH). The remaining anion (L-) reacts with the metal ions and in the case of divalent cations (M2+), it forms insoluble complexes of the type ML2. These uncharged complexes are soluble in various organic solvents. The fact that the corresponding hydrazones of isonicotinic and benzoic acid hydrazides with pyridine-2-aldehyde, form soluble complexes with the same cations is most probably due to the formation of charged complexes because of the lack of an ionized hydroxyl group. As these complexes are soluble in immiscible organic solvents, a systematic study of the factors involved in solvent extraction was carried out. Chloroform (E = 4.8), 1-octanol (E = 10.3) and 1-pentanol (E = 13.9) were used as extraction solvents. The concentration of a metal complex (ML,), in the organic phase, depends, on the concentration of the ionized ligand (L-) in the aqueous phase and its concentration consequently depends on the pH of the aqueous phase. It is evident that the main factor which regulates the extraction of a cation is the pH of the aqueous phase. On the basis of this fact, the distribution ratio of cations between the aqueous and the organic phases was studied as a pH function by the following procedure. Quantities of 5 ml of 2.0 x 10V5M solution of the studied cation were placed in stoppered Erlenmeyer flasks. These solutions, presaturated with the studied solvent, were buffered at the desired pH values under a constant ionic strength of 0.1 (final volume 10 ml). A volume of IO ml of 5.0 x low4 M solution of BIH or BBH in the studied solvent, presaturated with water, was added. The mixture was shaken mechanically for 12 hr in a thermostat at 25 + 1”. After settling for 4 hr and a complete separation of the two phases, the absorbance of organic phase was measured at the wavelength for maximum absorbance against a solvent blank. At the same time the pH of the aqueous phase was measured. The distribution coefficient D of the studied cations between the two equal volume phases, was calculated from the equation D = &%mx -A) where A was the measured absorbance of the organic phase and A,,, the absorbance for a complete extraction. This value was actually the sum of absorbances measured after successive extractions of the same aqueous phase, with the studied solvent solution of BIH or BBH. In all cases the absorbance after the second extract was almost near to zero.
EXTRACTION
METAL
HYDRAZONE
COMPLEXES
91
1
a s
0
-1
6.0
zo
a0
PH Fro. 5. Distribution ratio (log D) of (1) Ni(lI) and (2) Co(U) as a pH function. In both cases initial concentration of each cation in aqueous phase was 1.O x lo-” M and initial concentration of BBH in I-octanol was 5.0 X IO+ M.
All measurements were done twice and the average values are reported. From the obtained results it is concluded that: (a) Complexes of Zn(II)-BBH, Mn(II)-BBH, and Cd(II)-BBH were not extracted with chloroform, With I-pentanol and I-octanol an improvement was noticed but generally extraction of these complexes is considered unsatisfactory. (b) Complexes of Co(H)-BBH and Ni(II)-BBH were extracted quantitatively with I-octanol as shown in Fig. 5. (c) Complexes of Zn(II)-BIH, Mn(II)-BIH, and Cd(H)-BIH are not extracted with chloroform. They are extracted with 1-pentanol. Best results were obtained with Zn(II)-BIH complex as it is shown in Fig. 6. (d) Complexes of Zn(II)-BIH, Mn(II)-BIH, Cd(H)-BIH, Co(H)-BIH, and Ni(II)-BIH were also extracted with I-octanol and results are shown in Fig. 7. By this extraction cations of Co(H), Ni(II), and Zn(I1) can be determined separately by a spectrophotometric procedure. (e) Extraction with chloroform gave fairly good results only with the Co(II)-BIH and Ni(II)-BIH complexes. It was noticed that all the studied complexes were better extracted with I-pentanol and I-octanol, i.e., with solvent of higher polarity. In the case of Co(H)-BBH complex, it was extracted with chloroform but the Co(H)-BIH complex was not. This is probably due to the more polar molecule of BIH, where a nitrogen atom is present and the complex is less soluble in a lower-polarity solvent. Conversely, the Co(H)-BIH complex is better extracted with 1-pentanol than the Co(II)-BBH complex. This is also probably the reason why the BIH
92
VASILIKIOTIS
AND KOUIMTZIS
1.0 -
a % QO-
FIG. 6. Distribution ratio (log D) of (1) Cd(II), (2) Mn(II) and (3) Zn(I1) as a pH function. Initial concentration of each cation in aqueous phase was 1.0 x 10e5M and initial concentration of BIH in I-pentanol was 5.0 X 10m4M.
complexes are better extracted with 1-pentanol than with I-octanol. The extraction of a complex may be represented by the equilibrium MY$ + ~H4ot ML(o) + aH:,,, (1) The extraction constant or the equilibrium constant of the above reac-
4.01
51)
7.0
6.0
an
I
pn
FIG. 7. Distribution ratio (log D) of (1) Cd(II), (2) Mn(II), (3) Ni(Il), (4) Zn(II), and (5) Co(I1) as a pH function. Initial concentration of each cation in aqueous phase was 1.0 x lo-” M and initial concentration of BIH in I-octanol was 5.0 x 1O-4M.
EXTRACTION
METAL
HYDRAZONE
COMPLEXES
93
tion is K, = [ML,],,[H+]~/[M”+],[LH]~
(2)
If we restrict our considerations to the pH range where the formation of intermediate complexes with the ligand may be neglected, hydrolysis products, products of reactions with other complexforming anions in the aqueous phase are also neglected and providing that only the complex ML, is extracted while all Ml’+ remains in the aqueous phase, then the ratio [ML,],/[M”+], in Eq. (2), may be considered equal to the distribution coefficient D. In this case Eq. (2) is represented as
K, = DC[H+l::/[LHl:)
or
D = K,( [LH];/[H+]$).
(3)
If a = 2 then separate plots of log D against log [LH] and against pH should be linear and of integral slope 2. The noticed deviations in the studied cases (Figs. 5-7) are probably due to complexing factors between cations and anionic buffer compounds or hydroxyl ions especially at higher pH values. Work on analytical application of the studied extraction is in progress and results will be published in due time. SUMMARY Complex formation of o-hydroxybenzaldehyde isonicotinoyl-hydrazone with Co(lt), Ni(ll), Zn(ll), Mn(ll), and Cd(I1) has been investigated. These complexes are soluble in water-dioxane 1 : 1 (v/v) solutions and they were studied spectrophotometrically. The same complexes are soluble in organic solvents and studies on their extraction with chloroform, I-pentanol and I-octanol, for possible analytical application, are reported. In addition, complex formation of o-hydroxybenzaldehyde benzoyl hydrazone with Zn(II), and Mn(l1) is also reported. REFERENCES I. Grammaticakis, P., Contribution B I’Ctude spectrale des d&i&s azotes de quelques aldChydes et &tones aromatiques. VII. Hydrazones et acidylhydrazones. Blrll. Sot. Chinz. (Frtrncr)17, 690498 (1950). 2. Katiyar, S. S., and Tandon, S. N., I-isonicotinoyl-2-salicylidene as a new chelatometric reagent. Talunta 11, 892-894 (1964). 3. *ah, P. T., and Peoples, S. A., lsonicotinoyl hydrazones as antitubercular agents and derivatives for identification of aldehydes and ketones. J. Amer. Pl~arm. Ass., Sci. Ed., 43, 5 13-524 (1954). 4. Vasilikiotis, G. S., Study on the complex formation of isonicotinoyl hydrazones with some cations and their application in the analysis. Dissertation, University of Thessaloniki. 1968. 5. Vasilikiotis, G. S., Analytical applications of isonicotinoyl hydrazones. I. A new selective reagent for mercury. Microchem. J. 13, 526-528 (1968). 6. Vasilikiotis, G. S., and Tossidis, J. A., Analytical applications of isonicotinoyl hydrazones. II. Spectrophotometric determination of aluminum with l-isonico-
94
VASILIKIOTU
AND KOUIMTZIS
tinoyl-Z-salicylidene hydrazone as chromogenic reagent. Micro&em. J. 14, 380-384 (1969). 7. Vasilikiotis, G. S., Papavasiliou, 0. Ch., and Kouimtzis Th. A., Spectrophotometric and solvent extraction studies of the complexes of copper”, cobalt” and nickel” with some hydrazones. Chimica Chronica, Proc. IVth Conf.GreekChemists, Athens 1970, p. 107.