Synergistic effects in the solvent extraction of nickel salicylaldoxime

J. inorg,nucl.Chem.,1972,Vol.34, pp. 2041-2049. PergamonPress. PrintedinGreat Britain

SYNERGISTIC EFFECTS EXTRACTION OF NICKEL

IN THE SOLVENT SALICYLALDOXIME

A. P. RAO and S. P. D U B E Y Chemistry Department, Indian Institute of Technology, New Delhi-29, India

(First received 9 August 1971 ; in revised form 22 October 1971) S u m m a r y - T h e extraction of nickel with salicylaldoxime was studied. The adduct forming tendency of nickel salicylaldoxime with pyridine, c~-picofine, fl-picoline, quinoline and iso-quinoline was investigated and compared with those of zinc saiicylaldoxime and copper salicylaldoxime. The adduct forming tendency with various bases in the case of nickel is in the order: //-picoline > pyridine > iso-quinoline > quinoline > c~-picoline.

DYRSS~N and Hennicks[1] found that the partition of Ni(II) dimethylglyoxime into chloroform was not enhanced by quinoline or dodecylamine. Basolo and Matoush [2] have failed to isolate solid adducts of nickel dimethylglyoxime with pyridine. On the other hand they have isolated solid adducts of nickel salicylaldoxime. Csazar [3] has confirmed adduct formation of Ni(II) salicylaldoxime with various bases by magnetic and spectrophotometric measurements. In the light of the above observations we thought it worthwhile to investigate the solvent extraction behaviour of Ni(II) with salicylaldoxime (HA) in the presence of some heterocyclic bases (L) and compare it with the adduct forming tendencies of Zn(II) and Cu(II) salicylaldoximes. EXPERIMENTAL

Reagents All the reagents used were of analytical grade. Salicylaidoxime, B.D.H. indicator grade, was used without further purification. Pyridine, c~-Picoline, ~-Picoline, quinoline and iso-qninoline were dried and fractionated immediately before use. Benzene (B.D.H.) was purified by the standard methods [4]. Procedure: In every case the pH of the aqueous phase was measured after the extraction, for preliminary experiments showed that the buffering capacity of the aqueous phase was insufficient to maintain a constant pH throughout the range of concentration of the base investigated, because of their appreciable solubility in water. All experiments were carried out at 35-+0"I°C. The initial volumes of both phases were 20.0 ml. The concentration of Ni(II) in the system was 5 × 10-4 M, and the ionic strength of the aqueous phase was kept constant at 0.2 M using NaCIO4 (0.1 M NaCIO4 + 0.1 M buffer). The hydrogen ion concentration of the aqueous phase was maintained using sodium acetate-acetic acid buffer. The organic and aqueous solutions were placed in stoppered glass bottles and shaken in a thermostat (35 __0.1°(2) for one hour, which is the time required for equilibrium to be reached. Aliquots were pipetted from both phases for spectrophotometric estimation of Ni(II) with dimethylglyoxime [5]. 1. D. Dyrssen and M. Hennicks, Acta chem. seand. 15, 47 (1961). 2. F. Basolo and W. R. Matoush, J. Am. chem. Soc. 75, 5663 (1953). 3. J. Csazar, Acta. Univ; Szeged, Acta phys. Chem. 12, 117 (1966). 4. A. Weissberger, Technique of Organic Chemistry; Organic Solvents, Voi. VII. Interscience, New York (1955). 5. A. I. Vogel, A Text Book of Quantitative Inorganic Analysis, p. 794, Longmans Green, London (1962). 2041

2042

A.P.

R A O a n d S. P. D U B E Y

T h e s e p r o c e d u r e s were carried out carefully to avoid a n y contamination o f o n e p h a s e by the other. T h e remaining a q u e o u s p h a s e was taken for p H m e a s u r e m e n t s . T h e K d values were calculated according to the formula: K d - Total concentration o f Ni(II) in the organic p h a s e - Total concentration o f Ni(II) in the a q u e o u s phase.

Preparation o f the solid complexes and their adducts T h e metal chlorides were dissolved in methanol a n d m i x e d with a methanol solution o f salicylaldoxime (the ratio o f metal: salicylaldoxime being 1 : 2). T h e metal complex w a s then precipitated by adding dropwise a m m o n i a solution. T h e c o m p o u n d precipitated was then w a s h e d thoroughly with methanol, dried a n d analysed. T h e pyridine a d d u c t s of t h e s e [Ni(II) a n d Zn(II)] c o m p l e x e s were prepared by dissolving t h e m in pyridine and crystallizing. T h e crystals obtained were then removed, dried and analysed: NiA2 (found; C = 56.0%, H = 4.0%, N = 9.4% a n d Ni = 19.75%, calculated; C = 56.2%, H = 4.02%, N = 9.38% a n d Ni = 19-70%). NiA2PY2 (found; C = 63.1%, H = 4.8%, N = 13.0%, Ni = 12-4%, calculated; C = 63-1%, H --- 4.82%, N = 13.14% and Ni = 12.30%). ZnA2 (found; C = 54-9%, H = 3.98%, N = 9-2% and Z n = 21-50%, calculated; C = 55%, H = 3.93%, N = 9.17% and Z n = 21.42%). ZnA2PY (found; C = 59.0%, H = 4.3%, N = 11.0% and Z n = 17.00%, calculated; C = 59.3%, H = 4-42%, N = 10.93% and Z n = 17.00%). CuA2 (found; C = 55.3%, H = 3.8%, N = 9.3% and C u = 21.00%, calculated; C = 55.4%, H = 3-95%, N = 9-23% and C u = 20.92%).

Infrared spectra T h e i.r. spectra of the metal c o m p l e x e s and their adducts were recorded as mulls in Nujol using a Hilger and Watts i.r. spectrophotometer.

Thermograrns T h e t h e r m o g r a m s were recorded using a Stanton thermogravimetric balance at a constant heating rate o f 5°C/min.

A bsorption spectra

The absorption spectra were recorded on UNICAM SP 500 spectrophotometer using 3.5 cm cells. RESULTS AND DISCUSSION

The extraction of metal chelates can be described by (i) the plot of log Kd vs pH at constant reagent concentration in the organic phase which gives the number of protons released during complex formation. (ii) the plot of log Kd vs reagent concentration in the organic phase at constant pH. This gives the number of reagent molecules incorporated into the extractable complex. Figure 1 shows a plot of log Kdo vs pH. This gave a straight line of slope 2, indicating that two protons are released during complex formation. Figure 2 shows the plot of log Kdo + 2 log [H ÷] vs log [HA]org keeping the pH constant; this gave a straight line of slope 2, indicating that two molecules of H A are required for complex formation. This also indicates that Ni(II)-salicylaldoxime does not form an adduct with the excess reagent. Hence the extraction equilibrium for the Ni(II)-salicylaldoxime is given by: Ni+~aq) + 2HA~org~ ~-~ NiA~org~ + 2H+aqj.

( 1)

The equilibrium constant is given by:

Kex = [NiAz]or~[H+]Z[Ni+Z] -' [HA]o ~

(2)

Synergistic effects

1-5

-7-0

I-0

-~0

0-5

2043

-9"0

0

-I00 t

-0.5

--I1"0

-I.0

--12"0

-1.5

45

s-o

s.5

s.o

I 6s

I

-13"0

-~

Fig. 1. Ni(II)-0.01 M HA system, Y = log.Kd, X = pH.

Fig.

2.

J -2

I

Ni(II)-HA

I

I

I

I

-3

system,

Y=

IogKd + 2 log H +, X = log [HA]o,..

when no complexes are formed in the aqueous phase the distribution ratio is given by:

Kdo= [NiA2]o~[Ni+21-1.

(3)

Kdo = K e x [ H +]-2 [HA]2o,.,.

(4)

From (2) and (3)

Adduct formation with neutral donors can be written as Ni~az~ + 2HA(o~> + nL(o~) ~ NiA~Ln(o~g)+ 2H~q) 1"51 1"4

t.2 1.0 ! 0"8 0"6

0.4 I 0-2 0 -5.0

-,,'.~

-,;.o

-~.s

' -~.o

' -~.5

' -20

' -,.5

' -,.o

' -o.5

Fig. 3. N i ( l l ) - 0 - 0 1 M H A - B system, pH = 5.5: (1) /3-picoline, (2) pyridine, (3) ~picofine, (4) iso-quinoline, (5) quinoline (axis shifted by 0-5 units). Y = logKa . K ~ , X = log [ L ] ~ .

(5)

2044

A . P . RAO and S. P. D U B E Y

with the equilibrium constant /3,Kex = [NiA2LnJ0rg [H+] z [Ni +2]-1 [HA]o~ [L]o~

(6)

/3. = [NiA2Ln]org[NiA2]o~ [L]o~,

(7)

K d = {NiA2Ln] o~ [Ni +~-]aq1

(8)

where and

substitution of/3. and Kex into Equation (8) gives log Kd[H+]2 [HA]o~ = log Kex(1 '~/31 [L]or~ + t2 [L]2or~+/3, [L]~r~)

(9)

substituting for Kex from Equation (4), log K d . Kdo -1 = log (1 '~/31 [L]or~+/3~[L]oS~+fl,[L]~)

(10)

/31,132. . . . . /3, were evaluated by the procedures of Sekine and Dyrssen [6]. Since the partition co-efficients of the bases in the organic solvents are low, the concentration of the bases in the organic, phase were obtained by using the formula [7] (11) where PL = [L]o~/[L] and KLH = [L][H+]/[LH+], that is the protonation constant of the base. PL values of pyridine, a-picoline and/3-picoline were assumed to be the same as those of y-picoline which has a value 1.6 [8]. The PL and KLn values of quinoline and iso-quinoline were taken from the data of Irving and AI-Niami[9]. The calculated [L]org was used in the plots of log K d . Kdo -1 vs log [L]or~. Figure 3 gives the plots of log K d . Kdo -1 v s log [L]or~ for pyridine, a-picoline, fl-picoline, quinoline and iso-quinoline at constant HA of 0.01 M and pH of 5-55. The plots for pyridine,/3-picoline and iso-quinoline gave curves with a limiting slope of unity, and fit the normalised curve Y = log ( 1 + v); X = log v. This shows that NiAz forms an adduct with one molecule of the base in the range of concentrations of the bases investigated. The/31 values calculated are given in Table 1. Spectrophotometric study of the adduct formation The absorption spectra of nickel salicylaldoxime complex dissolved in benzene (at a fixed concentration of 0.0025 M) containing varying concentration of the bases were recorded. One of these spectra is given in Fig. 4. The pure complex has an absorption maximum at 620 nm. The absorption at this wave length decreases with increasing concentration of the bases becoming zero at very high 6. 7. 8. 9.

T. Sekine and D. Dyrssen, J. inorg, nucl. Chem. 26, 1727 (1964). H. Akaiwa and H. Kawamoto, ibid29, 1345 (1967). H. Irving and N. S. AI-Niami, ibid 27, 717 (1965). H. Irving and N. S. AI-Niami, ibid 27, 1671 (1965),

Synergistic effects

2045

t.O

0.9 I

I

0"8 07 0"6

_ 0.5 o

0

0.4 0-3

0:1 5

O0

I

I

i

i

[

600

i

i

i

Wavelength,

F i g . 4.

I 700

nm

750

Effect of fl-picoline on the absorption spectra of Ni(Sal)= in bemzene: (1) 0 . 0 M , (2) 0.01 M , (3) 0 . 0 2 M , (4) 0 . 0 3 M , (5) 0 . 0 5 M .

Table 1. Stability constants of NiA2 adducts with various N-base donors

Adduct forming base

log B1 values from solvent extn

log/~2 from UV-Visible spectrophotometry

log B2from

2.38 2.46 2-02

3.14 0.00 3.43 2.05 2-95

3.7 ( ± 0 . 0 8 ) 0.00 3"84 ( ± 0 . 0 9 ) -

Pyridine a-Picoline B-Picoline Quinoline Iso-quinoline

literature [ l 0]

concentration of the base. The absorption spectra of the complex in pure pyridine has an absorption maxima at 540 nm. Since there is no precipitation of nickel on adding the base to the benzene solution of the complex, it is evident that no complexes of the type NiL "+ are formed in solution. This proves that the decrease in absorption at 620 nm is due to adduct formation. Assuming the absorption at this wave length to be proportional to the amount of nickel salicylaldoxime, the equilibrium constants for the equilibrium; N i A 2 + 2 L ~ NiA2Lj were calculated. The calculated/~ values for this reaction for different concentrations agreed with one another showing the formation of NiAeL~. The calculated fl~ values are given in Table 1, along with those obtained by other authors. 10. M . F r a n c e s c o , R . V i n c e n z o , P.

,

J I N C vel. 24, no. 6 - - I t

Tecla and P. Lorrenzo, Anal. Chim., Rome 58, 7 2 5 ( 1 9 6 8 ) .

2046

A.P. RAO and S. P. DUBEY

0"40

0.35 ~~, 2

5

0-25 -

.~ 0-20

8 ..

OI5 o,o

o.o~ 0

400

.,~:~ I

I

450

I

500

I

I

550 600 Wovelength,

650 nm

I

700

I

I

750

800

Fig. 5. Effect of pyridine on the absorption spectra of Cu(Sal)2 in benzene: (1) 0-0, (2) 0-01 M, (3) 0.02 M, (4) 0.05 M, (5) 0"I M. Adduct formation constants of zinc salicylaldoxime were taken from our previous

paper[1 1]. The adduct formation constants for copper salicylaldoxime were not available in the literature, so we have tried to obtain the adduct formation constants spectrophotometrically. These were obtained just like those of NiA2. But here, unlike NiA2, the absorption spectra of CuA2 and CuA2Ln overlap very much. So we have tried to obtain the adduct formation constants from the increase in optical density at 680 nm. The spectra of CuA2 in benzene in the presence of 12C H0

~"~

I

i0o-- 3_L4

o,F 80

\\ '

7O

.} 6o ~

5O 4O 3O

I£

" ~ I

o

,0o

~;o

~o Temperature,

Fig. 6. T h e r m o g r a m s

~;o

5 0 '0

6 0' O

°C

for: (1) Ni(Sal)=, (2) Ni(Sal)2Py~, (3) Zn(Sal)2, (4) Zn(Sal)2Py.

11. A. P. R a o and S. P. D u b e y , Talanta (in p r e s s ) .

Synergistic effects

2047

pyridine is given in Fig. 5. All these spectra gave a single isosbestic point showing the formation of a 1 : 1 adduct. The stability constants were calculated assuming 1 : 1 adduct. The concentration of the adduct for a given concentration of the base was calculated using the formula

[Adduct] = [Cu]o • ~ - Eo

(12)

E~ -- Eo

where [Cu]o is the total concentration of the copper complex, ~ = molar extinction coefficient in the presence of the base, E~ = molar extinction coefficient in the pure base and ~o = molar extinction coefficient in the absence of the base. Because of the small changes in optical density values, the calculated stability constants will not be accurate and only give a rough estimate of the stability constants. The 131values for the adducts of Ni(II) salicylaldoxime, Zn(II) salicylaldoxime and Cu(II) salicylaldoxime are given in Table 2 along with the stability constants for the pure complex. Table 2. Stability constant values of the adducts of NiA2, ZnA2 and CuA2 log stability constant of the pure complex from Complex literature [ 13] NiA2

14"3

ZnA2

13.5

CuA~

21 "5

Adduct

log/3t of the adduct from solvent extn

NiAe.pyridine NiA2.¢-picofine NiA2.fl-picoline NiA~.quinoline NiA~.isoquinoline ZnA2.pyridine ZnA~.ol-picoline ZnA~.B-picoline ZnA2.quinoline ZnA~.isoquinoline CuA~.pyridine CuA~.~-picoline CuA~.~0-picoline

2"38 2'46 2.02 4.26" 4.14" 4.60* 3.74" 4.08" 0.5181 - 0.366t 0-634t

*Taken from Ref. [ 11]. tThese values are from spectrophotometric data.

It can be seen from the above results that while N i A 2 f o r m s an 1 : 2 adduct in spectrophotometric studies, it forms 1 : 1 adduct in solvent extraction in the range of base concentrations investigated. Akaiwa and Kawamoto [12] during their studies on the synergistic extraction of Ni(II)-thenoyl trifluoro acetone with neutral bases also found the formation of 1 : 1 adducts up to a certain concentration of the base. I n the c a s e o f s y n e r g i s t i c e x t r a c t i o n in p r e s e n c e o f q u i n o l i n e a n d a - p i c o l i n e , it w a s n o t i c e d , t h a t the e x t r a c t i o n i n c r e a s e s u p to a b a s e c o n c e n t r a t i o n o f 10 -2 M. 12. H. Akaiwa and H. Kawamoto, J. inorg, nucl. Chem. 31, 1141 (1969). 13. K. Burger and I. Egyed, ibid27, 2361 (1965).

2048

A . P . R A O and S. P. D U B E Y

But a destruction of synergism occurs after this. This is most probably due to the formation of complex cations of the type NiLn +~ in the aqueous phase. Akaiwa and Kawamoto[12] have also made similar observations at high concentrations of these bases. With all the metal ions the mono adduct forming tendencies with various heterocyclic base is: fl-picoline > pyridine > a-picoline > iso-quinoline > quinoline. This is the order of decreasing base strengths of these donors. The apparent discrepancy in the position of a-picoline is due to the steric hindrance produced by the a-methyl group. The stabilities of the adducts of these elements decrease in the order: Zn(II) > Ni(II) > Cu(II). Similar observations have been made on the adducts of metal fl-diketenates [ 14]. The thermograms of Ni(II) and Zn(II) chelates and their pyridine adducts are given in Fig. 6. Zinc salicylaldoxime decomposes above 280°C and becomes oxide at 440°C. Its adduct looses pyridine at 160°C, and the first step corresponds to the formation of ZnA2 from ZnA2Py. The second step corresponds to the conversion of ZnA2 to ZnO. Nickel salicylaldoxime decomposes above 240°C and becomes NiO at 400°C. Its adduct looses pyridine at 160°C; the first step corresponds to the formation of NiAz from NiAz.Py2 and the final step corresponds to the formation of NiO from NiA2. Table 3. Infrared frequencies of metal chelates and their adducts in cm -~ NiA2

NiA~Py2

ZnA~

ZnA2.Py

Assigned group O - - H deformation C-~-N stretching coupled to C = C stretching

1640vs 1600vs,b

1644vs 1616vs

1600v s

1650 1608v s

1556vs

1592vs,b 1536s,b

1548s,b

1580s 1560m

1340vs

1344vs 1312s,b 1212

1316s 1296vs -

1302 ] - J 1248s 1220vs

1296vs,b 1256s -

Pyridine ~N stretching coupled to C = C stretching

C - - H inplane vibration

Pyridine mixed with N - - O stretching

1200s

1184vs

1198s

1160sh l 148sh 1125vs,b 1040 1020vs 976m,b

1152vs l 120s 1072vs 1036 1012vs 960s

1148m,sh 1116vs 1000vs 960m

948m 916vs

916w

1160s,b ] ~ I 120s,b J 1072vs 1044vs 1016vs 980m ] I

916vs

N - - O stretching Pyridine and O-disubstituted benzene ring vibrations. Pyridine benzene ring vibration ---(C--O) stretching N - - O stretching

-

s = strong, vs = very strong, w = weak, b = broad band, m = medium, sh = shoulder. 14. H. Irving, In Solvent Extraction Chemistry (Edited by D. Dyrssen, J. O. Liljenzin and J. Rydgberg) p. 91. North-Holland, Amsterdam (1967).

Synergistic effects

2049

The temperature at which the adducts loose the pyridine definitely shows that the pyridine molecules are bound to the metal directly in the chelate. The i.r. absorption frequencies are given in Table 3. The absorption frequencies definitely show the frequencies of the pyridine in the adducts. The i.r. frequencies of metal salicylaldoxime were reported previously by Ramaswamy et al. [ 15]. Acknowledgements-One of the authors (S.P.D.) isthankful to Council of Scientific & Industrial Research, New Delhi (India) for providing financial assistance.

15. K. K. Ramaswamy, C. I. Jose and D. N. Sen, Ind. J. Chem. 5, 153 (1967).