CROATICA CREMICA ACTA CCACAA 59 (2) 443-449 (1986)

CCA-1657YU ISSN 0011-164:3

UDC 546.711OriginaL Scientific Paper

Effect of Several Auxiliary Ligands on the Extractionof Manganese(II) With 4-Benzoyl-3-methyl-l-phenyl-5-pyrazolone

Visvanathan Ramesh and G. N. RaoChemistry Department Indian Institute of TechnoLogy Hauz Khas,

New DeLhi-ll0016, India

Received April 12, 1985

The effect of 2-methyl pyridine N-oxide, 4-methyl pyridineN-oxide, pyridine N-oxide, 8-aminoquinoline, dibenzyl sulfoxideon the extraction of manganese(II) by 4-benzoyl-3-methyl-1-phe-'nyl-5-pyrazolone (BMPP) in benzene from an aqueous bufferedsolution was studied. Synergistic enhancement was observed inall systems. Equilibrtum extraction constants and adduct formationconstants were calculated. The results showed that synergisticextraction is due to the formation of adducts such as Mn(BMPP)2Bwhere B represents the auxiliary ligand.

INTRODUCTION

While the extraction of some metals with BMPP has been reported(Thakur and Rao, Zolotov), no detailed report on the extraction of manga-nese(II) with BMPP using auxiliary ligands has appeared so faro In a generalsurvey of the extraction of manganese(II) with different chelating agents a pRhalf (pR at which half of the total metal ion is extracted with 0.01 M BMPP)value for extracting manganese(II) with BMPP in benzene has been mentioned.In the present paper results of the study of the extraction of manganese(II)with 4-benzoyl-3 methyl-1 phenyl-5-pyrazolone (BMPP) using different auxi-liary ligands, such as 2-methyl pyridine N-oxide, pyridine N-oxide, 4-methylpyridine N-oxide, dibenzyl sulfoxide and 8-aminoquinoline are reported.

EXPERIMENTAL

Pyridine N-oxide (Fluka), 2-methyl pyridine N-oxide (Fluka), 4-methyl pyri-dine N-oxide (Fluka), 8-aminoquinoline (Eastman Organic Chemicals), Dibenzylsulfoxide (Fluka) were used. The ligand (BMPP) was prepared according to themethod of Jensen! by using 1-phenyl-3-methyl-5-pyrazolone, i. e. MPP (B.D.H) andbenzoyl chloride (Fluka). Acetate buffers were used for pH variation studies. Aconstant ionic strength of 0.1 M was maintained by us ing potassium nitrate solution.Ten ml of the aqueous layer containing two ml of fifty ppm manganese sulphatesolution, five ml of buffer solution and one ml of one molar potassium nitratesolution was equilibriated with ten ml of benzene containing BMPP and the auxiliaryIigand at required concentrations for thirty minutes in a thermostatic shaker at30 ± 1 "C. After equilibriation the two layers were allowed to settle. Preliminaryexperiments indicated that equilibrium was attained after shaking for ten minutesbut a shaking time of thirty minutes was employed as a precautionary measure.The concentration of manganese in the aqueous layer was measured by an SP 191atomic absorption spectrophotometer. The pH of the aqueous layer was measured

444 v. RAMESH AND G. N. RAO

by an expanded scale pH meter (ECIL India). Partition coefficient Kd is definedas the total concentration of metal in the organic phase divided over the totalconcentration of the metal in the aqueous phase.

RESULTS AND DISCUSSION

Extraction behaviour of manganese(II) with 4-benzoyl-3-methyl-1-phenyl--5-pyrazolone (BMPP) was studied by determining Kd values for differentpH values keeping the ligand concentration constant at 0.01 M BMPP. Theplot of log Kd vs. pH gave a straight line with a slope of - 2. A similarstudy of variation of Kd with ligand concentration at constant pH (6.1) indicatesthe number of ligand molecules involved in the extracted species. Since theslope of the plot of log Kd vs. pH at constant ligand concentration is - 2and the slope of log Kd VS log [HT] at constant pH is also - 2, the extractionequilibrium may be represented as

(I)

where HT represents the ligand BMPP. Equilibrium constant can be cal-eulated, as usual from the equation

(2)

However, manganese(II) present in the aqueous phase may exist in theform of complexes with aeetate, namely [MnrAc)"]. Therefore, the total eon-eentration of manganese in the aqueous phase is given by

[MnIl].q = [Mn(Actlaq + [Mn2+laq

The distribution ratio is given by

Kd = [Mn(T2)lorg/([Mn2+laq + [Mn(ActJaq)

[MnT2loraK - ~d - [Mn2+laq (1 + tJl [Ac ])

(3)

(4)

From the stability eonstants it is calculated that total Mn(II) in the aqueousphase is made up of seventy percent manganous ion and thirty pereent of[MnrAc)"]. (JI the change in the relative eoncentration of [MntAc)"] to man-ganous ion is small when the pH is varied. The value of log [Mn(Ac)+l/[Mn~+lwas calculated as a function of the observed pH by using the stability constantfor [Mn(Ae)+] (Table 1.)12

TABLE I

Relative Concentrations of Acetate Complexes

pH 4.49 4.53 4.66 4.87 5.21

[Mn(Actllog [Mn2+f 0.17 0.18 0.17 0.16 0.13

Henee, from equation (4) the relationship between Kd and Kd' is given by

Kl [MnT2lorgKd = . where Kd' = ---"--'-'-"-

1 + tJl [Ac 1 [Mn2+laq(5)

MANGANESE(II) EXTRACTION 44:)

From equations (2) and (4) we get

log Kex = log Kd - 2 log [HT]org- 2pH + log (1 + (JJ [Acj) (6)

The value of Kex was calculated from (6) using the experimental values ofKd, [HT] and pH. The effect of adding auxiliary ligands on the manganese(II)extraction with BMPP was similar1y investigated by determining the Kdvalue as a function of the concentration of auxiliary ligand (B) at constantpH and BMPP concentrations. From the plot of log Kd vs. log [Blorgthe numberof molecules of B incorporated in the extracted species was determined.Extraction of manganese(II) in the presence of auxiliary ligand B may berepresented 'ils

with the equilibrium constant Kex given by

Kex' = [MnT2Bmlorg[H+laq2/[Mn2+Lq

[HTlorg2[B1ort (8)

From equations (5) and (8)

log Kex' = log Kd - 2 log [HTlorg- 2 pH - m log [Blorg+ log (1 + (JJ [AcI)where

Kd = [MnT2Bmlorg/[Mn2+laq(1 + (31 [Ac-])

The adduct formation constant (Ks) for the equilibrium

is given by

(9).

log Ks = log Kex' -log Kex (la)

One of the possible side reactions caused by adding a pyridine base is theprotonation of the base in the aqueous phase where [Mn]total« [B]tota], thefollowing equation is obtained by mass balance

[Bltotal= [Blorg+ [BLq + [BH+laq

into which the distribution coefficient PB

[BlorgPB = [B]aq

(11).

and dissociation constant KBH for the protonated form of the base are intro-duced and the resulting situation is given by

(12).

where a B(H) is a variable defined only by the concentration of the hydrogenion and the kind of the base [B]orgfor pyridine N-oxides has been calculatedusing equation (12). The valu es of PB and pKBH for the pyridine N-oxides are-listed" in Table II.

446 V. RAMESH AND G. N. RAO

TABLE II

.Partition Coeificients (PB) and Dissociation Constants pKBH VaLues of the HeteroCycLic Base N-Oxides*

Auxiliary Ligand

Pyridine N-oxide2-methyl pyridine N-oxide4-methyl pyridine N-oxide

0.00260.01430.0034

0.6021.0341.086

* Estimated uncertainty in numerical values is ± 0.1 unit.

Adducts formation constants (Ks) and the values of K'ex are listed in Table III.

TABLE III

.Extraction Constants and Formation Constants of the Adducts Formed Betweenthe CompLex Mn[BMPP12 and Various AuxiLiary Ligands

Auxiliary ligand

Pyridine N-oxide2-mehyl pyridine N-oxide4-methyl pyridine N-oxidedibenzyl sulfoxide8-amino quinolinenil

-3.89-4.38-3.62-5.50-5.63-8.10

4.213.724.482.602.41

* Estimated uncertainty in numerical values is ± 0.1O unit.

Figure 1 shows the plots of log Kd vs. log [B]orgfor 2-methyl pyridineN-oxide (pH = 5.60), 4-methyl pyridine N-oxide (pR = 5.70) and pyridineN-oxide (ph = 5.60) at constant ligand concentration (BMPP = 0.01 M). Onemole of 2-methyl pyridine N-oxide, 4-methyl pyridine N-oxide or pyridineN-oxide is present in the extracted adduct as indicated by the slope value of- 1. Figure 2 shows the plots of log Kd vs. log [Blorgfor dibenzyl sulfoxide(pH = 5.0) and 8-amino quinoline (pR = 5.50) at constant ligand concentration(BMPP = 0.01 M). One mole of dibenzyl sulfoxide or 8-amino quinoline ispresent in the extracted adduct as indicated by the slope value of - 1. Plotsof log Kd vs. log [RTl at constant [B]org in all cases gave a slope of - 2indicating the presence of two moles of BMPP in all the adducts.

The main factors affecting the synergistic extraction of a metal chelateare considered to be the stability and the organophilic property of the resultingadduct. A competing reaction between the formation of the adduct in questionand that of BR+ also affects the extent of synergism. One of the major factorsaffecting the stability of a metal complex is the basicity of the ligand, whichis essentially the same as the affinity of the ligand towards protion. Theformation constants of the adducts decreased in the order 4-methyl pyridineN-oxide > pyridine N-oxide> 2-methyl pyridine N-oxide > dibenzyl sulfo-.xide > 8-amino quinoline. Akaiwa and Kawamoto" showed that stabilities of

MANGANESE(II) EXTRACTION 447

0.4

0.2 c

bO a

-o -0.2

'"en.s-0.4

-0.6

-0.8

-3.6 -3.4 -3.2 -3.0 -2.8 -2.6 -2.4 -2.2 -2.0 -1.8

log [BJbrg

Figure 1. Plot of logKd vs. log [Blorg for the extraction of Mn(II) with 10 mMBMPP in benzene. [Blorg represents (a) 4-methyl pyridine N-oxide (p'H= 5.70)

(b) pyridine N-oxide (pR = 5.60) (c) 2-methyl pyridine N-oxide (pR = 5.60).

the adducts of Mn(II) thenoyltrifluroacetonate with pyridine bases follow thisorder. The stability constants of metal complexes having structurally similarligands often show a roughly linear dependence on the basic strength of theIigands." Major deviations from the expected trend are attributed to thesteric effects.P Other deviations from normal rules of the stability constantsmay probably be caused by the presenee of TC bonds.f These results can beinterpreted by assuming metal to ligand back bonding, which can be achievedby back donation of electrons from the half filled metal d-orbitals to theempty TC* antibonding orbitals of the N-O bonds in the ligand.t? The energylevel of this TC* orbital increases when a methyl group is introduced in thefourth position of the ring, thereby decreasing the energy match between thehalf filled orbitals of the metals and the TC* orbital and thus decreasing thecontributioi1 of back bonding. Lower values of log Ks for 2-methyl pyridineN-oxide and 8-aminoquinoline may be attributable to the steric effects ofthese bases. In fact, 2-methyl-pyridine adduct of bis (acetyl acetonato) man-ganese(II) has been reported to be unstable compared with its pyridineadduct."

448

0.2

O

-0.2

-O.~-o

tx:eno

-0.5

-0.8

-1.0

-1.2

v. RAMESH AND G. N. RAO

a bo

-2.0 -1.8 -1.6 -I.~ -1.2 -1.0 -0.8

Log [BJorg

FIG. 2.

Figure 2. Plot of log Kd vs. log [BJO,.gfor the extraction of Mn(II) with 10 mMBMPP in benzene. [BJorg represents (a) dibenzylsulfoxide (pH = 5.0) (b) 8-amino-

quinoline (pH = 5.50).

REFERENCE S

1. B. S. Jen s e n, Acta Chem. Scand. 13 (1959) 1958.2. N. S. Al - N i ami, A. R. Al - K ara g h o u I i, and S. M. A I i w i, J. Inorg.

NucL Chem. 35 (1973) 577.3. J. S. Tha k u r and G. N. Rao, J. Sci. Ind. Res. 34 (1975) 110.4. Yu. A. ZoI o tov, Extraction of Chelate Compounds, Humprey Science Pu-

blishing Co. Inc., Ann Arbor, Michigan. (1970).5. H. K a w amo t o and H. A kai w a, J. Inorg. Nucl, Chem. 30 (1968) 3065.6. D. D. Per r i n, Organic Complexing Reagents, Interscience Publishers, New

York (1964).7. Y" Mar c u s and A. S. K e r t e s, Ion Exchange and Solvent Extraction of

Metal Complexes, Wiley Interscience, London (1969).8. E. B. S and e 11 and H. O n i s h i, Photometrie Determination of Traces of

Metals, Wiley Interscience, New York (1978).9. N. S. Al - N i ami and H. A. A. R o s u 1, J. Inorg. Nuci. Chem. 36 (1974) 2051.10. L. Rom a and G. N. Rao, Proe. Indian. Acad. Sci. Chem. Sei. 92 (1983) 167.11. E. Uh 1e man n, B. Ma a c k, and M. Raa b, AnaL Chim. Aeta. 116

(1980) 153. ,12. A. R i n g b o m, Complexation in Analytieal Chemistry, Sangyo Tosho, (1965).13. H. I r v i n g and H. R o s s o t t i, Aeta Chem. Seand. 10 (1956) 72.14. J. J. R. Fra u s t oDa S i 1v a and J. G o ne al ves, J. Inorg. Nucl, Chem.

28 (1966) 125.15. T. Se k i n e and T. Tak a h ash i, Buil. Chem. Soe. Japan. 50 (1977) 3413.16. D. P. G rad d o n and G. M. Mo c k I e r, Aust. J. Chem. 17 (1964) 1119.

MANGANESE(II) EXTRACTION 449

SAŽETAK

Utjecaj nekoliko pomoćnih liganda na ekstrakciju mangana(II) s 4-benzoil-3-me-toksi-l-fenil-4-pirazolonom

Visvanathan Ramesh and G. N. Rao

Proučavan je utjecaj 2-metilpiridin-N-oksida, 4-metilpiridin-N-oksida, piridin--N-oksida, 8-aminokinolina i dibenzilsulfoksida na ekstrakciju manganatl I) 4-ben-zoil-3-metil-l-fenil-5-pirazolonom (BMPP) u benzenu iz vodenih puferiranih otopina.

Izračunane su konstante ekstrakcije i konstante nastajanja adukata. Sinergi-stički efekt uočen je u svima proučavanim sistemima, a postignut je nastajanjemadukata Mn(BMPPl2B, u kojima je B pomoćni ligand.