Indian Journal of ChemistryVol. 16A. June 1978. pp. 504-506

Study of Competitive Reactions by Solvent Extraction: Complexes ofZinc with Oxalate, Lactate, Glycollate & Tartrate.

PUSHPARAJA* & M. SUDERSANANAnalytical Chemistry Division, Bhabha Atomic Research Centre, Trornbay, Bombay 400085

Received 6 August 1977; accepted 15 January 1978

Complexes of zinc with oxalate, lactate, glycollate and tartrate have been studied by themethod of solvent extraction using thenoyltriftuoroacetone as the auxiliary ligand. The stabi-lity constants of the above complexes as well as of that with thenoyltrtftuoroacetone have beenevaluated using a rigorous equation.

CONNICK and McVeyl were the first to suggestthe possibility of studyir g non-extract» blecomplexes of metals by the method of

competitive re •.ctions. Sekine and coworkers+sha ve used this method to study the complexes ofeuropium. lanthanum. etc. with some inorgai.icIigands using theroyItrifluoroacetor.e (HTTA) orHTTA-TBP mixtures c s the auxiliary ligand.Complexes of cobblt "rid zinc with some organicJigar.ds ha ve also been studied by Schubert ct al.4by ion exchange and solvent extraction techr.iques.The limi ta tior.s in the a pplica bility of the methodsuggested e,irlier- under normr I experimental con-ditions ha ve been pointed out" a nd the rigorousexpression ho s been recommended for USe. Thispaper presents a study on the complexes of zincwith oxalate, lactate, glycollate and tartrate bythe method of competitive reaction using thetechnique of solvent extraction.

Materials and MethodsGlycollic, lactic (Riedel De Haen AG. Seelze,

Hannover) and oxalic (BDH, AR) acids 8S well <ispotassium sodium tartra te (E. Merck, GR) wereused without further purification and the stocksolutions were estirna ted volumetricclly. Ther.oyl-trifiuororcetone (HTTA) (Koch-Light L.bs) W2Sused a s the auxiliary ligand with chloroform(Su rabhai-Merck, GR) as the diluent, Zinc wasused in the form of 65Zn obta ined from IsotopeDivision, BARe. The ionic strength was main-t.. incd constan t a t 1·0 by the addition of requisite<1 mounts of sodium perchlora tc.

The aqueous phase (10 ml) containing the tracermetal ion, complexir g ligand, perchloric acid orsodit.m hydroxide to v,ry the pH and requisiteamount of sodium perchlorate w: s equilibratedfor 5 hr at room temperature (23°± 1°) with anequal volume of the organic phrse contairirgHTTA. The two phases were then allowed toseparate. The pH of the aqueous phase wrsmeasured using a Beckman Exp..ndomatic SS-2 pHmeter (.Mjs Beckrn; n Ir.strumer, ts Ir.c.). Aliquots

"Health Physics Division, Bhabha Atomic Research Centre,Trombay, Bombay 400085.

504

(1 ml er ch of the two phases were estirnr ted forzinc by Y-countirg usirg a sirgle channel a nc lyscrwith a well type th. Ilit.m ; ctiva tcd sodium iodidecrystal (Mjs Electronics Corpor.tion of Ir.dia ). Thereadings were corrected for b; ckgrour.d r.ctivity.

Results and DiscussionZinc-HTTA system - Although the extrr ction of

zir.c w: s studied by Akiba et al.6 ar.d ot11Crs7-9 whileinvestiga tir.g the c;dduct/rnixed complex forma tion ,the system W8 s reinvestiga ted to obta in distribu tionda ta under the present experimental conditionsfor use in the study of aqueous phase complexesbv the method of competitive rc. ctiors.

-The extraction of zir.c by HTTA in chloroformw8S studied as a fur.ction of pH. At low cor.cen-tratior s of zir.c, the forrnr.tion of polynucleer ccm-plexes and hydrolysis in the pH r,; r ge of the presentstudies could be neglected. The distribution ratio,Do> of zinc ill the preser.ce of HTT A alone is given by

Do = ~~~?J.!l = P2~2[A]2 ... (1)[ZnJ+[ZrAJ+ . .. :i~n[AJn

owhere [AJ is the cor.ccr.trr tion of the ar.ion of HTTA,[l"s refer to the ovcrnIl stability cor.str.r.t s of thecomplexes ai.d P2 is the pa rtition cocfficicr.t of ZnA2•

The cor.ccntra tion of the union of HTTA wasevaluated from the pH of the solution, the dissocia-tion constant (10-6•2)1 ar.d the partition coefficient(69)8 of HTTA. The initial slope of two for a plotof log Do vs PA (Fig. 1) indicated the extractedspecies to be ZnA2. The slope decreased ,·t higher[ligand] due to water-soluble complexes. Thesta bility cor.sta nts were cr.lcula ted by the gr; phica lmethod of Rydbcrg-? ; s log ~l = 2·42 a r.d log~2 = 7·02. The equilibrium constant for the ex-tra ction reZction

k,Zr.2++2[HTTA]o ~ [Zn(TTA)2Jo+2H+ ... (2)W;iS calculated as 10-7•45 which compared well withthe reported values=" considerir g the ionic strergthand the medium used.

Method of competitive reactions - The techniqueof solvent extraction has been used for the study

PUSHPARA]A & SUDERSANAN: STUDY OF COMPETITIVE REACTIONS

'.0

0 00

00 0

000-' -'.0

0

-10

~O 40,A

Fig. 1- Plot of log Do versus PA for Zn-HTTA system

of competitive complex formation between a centralmetal ion, say, zinc and two ligands, A and L. Thedistribution ratio, D, in the presence of both theligands can be written <IS

[ZnA2]oD [Zn]+[ZnALJ +[ZnA2J+ ... + [ZnL]+[ZnL2]+

... (3)p2~2r AJ2 _.. (4)" ..

~[3n[A]"+~[3~[L]"o 1

where [3~ refers to the overall stability constantsof ZnL complexes. Eqs. (1) and (4) can becombined to get5

II

Fo = P2[32[A]2(D-l_Dii1) = ~[3~[L]" ... (5)1

The rigorous Eq. (5) which takes into account theaqueous phase complexes of the auxiliary ligandhas been used in the present studies.

Zinc-oxalatellactate complexes - The distributionratio, D, of zinc was measured at different [oxalate]and [lactate] at an ionic strength of 1·0. The con-centration of oxa late/lacta te ior:s was calculatedfrom the pH of the solution and the PK values of1·27 and 4·27 for oxalic acid and 3·86 for la ctic acid-'.The corresponding value of Do was obtained fromthe plot of log Do vs PA (Fig. 1). The Fo functionswere calculated from EC]. (5) and a plot of log Fo'vs pL resulted in a single line (Fig. 2) indicatingthe absence of hydroxy complexes. The Fo functionsobtained from the smooth curve were solved forthe stability constants by the graphical method(Fig. 3). The values of the stability constants a represented in Table 1 along with the reported valuesfor comparison.

Zinc-glycollateftartrate complexes - Experimentswere carried out in a simile r manner. The PK valueof glycollic acid was determined'P under iden tica 1conditions by the pH titration technique as 3'30,in good agreement with the value of 3·35 reportedby Lefebrve-". The PI{ values-! of 2·88 and 3·94were used for the calculation of [tartrate]. TheFo functions calculated with the help of Fig. 1 arepresented in Fig. 2 (curves 3 and 4) and these weresolved for the stability constants by the graphicalmethod (Fig. 4). The stability constants are givenin Table 1. The agreement is good for all the

LACTATE

2 OXALATE

GLYCOLLATE2.' '.0• TARTRATE

1.11pL

Fig. 2 - Plots of log Po versus pL

.•..-._---_...._. . I

2 4 e[L), 102 M

ZINC - LACTATE ZINC -OXALATE4..~.••." 3

Fig. 3 - Solution of Fj function of curves 1 and 2 in Fig. 2

.., •.o 0- - ZINC - GI.YCOLLATE. .... -•.. •..

~

.c'5

e 3

4 2'0

2 , L..:F:.!..,_~:-- ..••....•

F)

8 12

[LJ. '031'4

Fig. 4 - Solution of Fj function of curves 3 and 4 in Fig. 2

,e 24

systems except the [33 va lue for la eta te ar: d [3, forglycolla te.

The stability constants for the Ia ctn te a ndglycolla te complexes are of the same order whilethose of oxala te and ta rtr a te complexes a re higher.This can be attributed to the bidentate nature ofthe liga rids and the results also indica te theformation of t.nior.ic complexes. The stabilityconstants reported for the higher complexes ofla eta te a Ed glycolla te (1 re un certa in in view of theuncertainty in the me('scnmer ..t of the distributionra tio at higher cor centre tion of the liga r.d. Themethod of solvent extrr ction is most suite: ble forthe study of lower complexes where; s potentio-metry and polarogr2 phy are more useful for thestudy of higher complexes.

50~ f

INDIAN J. CHEM., VOL. 16A, JUNE 1978

System

Oxalate

Lactate

Glycoliate

Tartrate

TABLE 1 - VALUES OF STABILITYCONSTANTSOF ZINC COMPLEXES

Method= Temp. II. Log stability constant] Ref.---------------------

[11 [12 [13 [1.

dis 23 1 (NaClO.) 3'26 6'63 ++H 25 1 (KN03) 3·44 6·48 7-24 15dis 25 0·16 (NaCI) 3·85 6·37 4

E, sol 25 0 4-68 7·04 16dis 23 1 (NaCIO.) 1·93 2·83 (4'53) ++H 20 0'2 (KCI) 1'86 14qh 25 1 (NaCIO.) 1-61 2·85 3·15 17

dis 23 1 (NaCIO.) 1'85 3·32 3·80 (6·90) ++qh 25 1 (NaCIO.) 1·92 2'93 3·00 4·04 18pol 30 0.5 (KN03) 1-46 2·65 3·05 3·23 20pol 18 2.0 (NaCIO.) 1-92 2-94 3-48 3·00 19

dis 23 1 (NaCIO.) 3-22 ++dis 20 0·1 (KCIO.) 2·69 21dis 25 0·2 (NaC,IO.) 3·34 5.19 22

*dis, distribution method; pol, polarography; H, potentiometry using glass electrode; qh, quiuhydrone electrode; E, sol,Emf, solubility measurements.

[The reported values are the mean values and the accuracy is about ±0·02 to ±0·05 log unit.tPresent work.

AcknowledgementThe authors wish to thank Dr A. K. Ganguly,

Director, Chemical Group, and Dr A. K. Sundaram,Analytical Chemistry Division, BARC, for valuableguidance and encourr gement.

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