Sudersanan, M.

Sundaram, A. K.

English

NOPR

indian Journal of ChemistryVol. 15A. August 1977. pp, 734-737Synergism in the Extraction of Indium by a Mixture ofDi-2-ethylhexylphosphoric Acid & a ~-DiketoneM. SUDERSANAN & A. K. SUNDARAMAnalytical Chemistry Division. Bhabha Atomic Research Centre, Bombay 400085Received 5 N ouember 1976; accepted 5 ] anu,ary 1977Synergism in the extraction of indium by a mixture of di-2-ethylhexylphosphoric acid and aP-diketone like thenoyltrifluoroacetone, benzoyltrifluoroacetone and dibenzoylmethane has beenstudied. The results indicate a new type of synergism in which the p-diketone replaces part ofthe alkylphosphoric acid. The nature of the complexes as well as their equilibrium constantshave been evaluated. The effect of temperature on the extraction has also been studied and thethermodynamic parameters have been calculated. The results have been discussed in terms ofthe entropy factors involved in the extraction process.EXTRACTION o~ in~ium by various ext.ra~tantshas been studied In these laboratories'. Inthe course of our investigations on the ex-traction of indium by mixtures of TBP or TOPOwith rhenovtrifluoroacetonc (HTTA), no enhance-ment was observed in the case of extraction byTBP whereas a considerable increase in extractionwas observed with a commercial sample of TOPO.Such an enhancement due to adduct formation isunlikely in the case of metals like indium .whichforms coordinately saturated complexes. This wasalso confirmed from experiments conducted athigher concentrations of the metal ion when theextraction appeared 'normal' as expected on thebasis of the concentration of HTT A alone. Theresults are interesting in view of the pronouncedsynergism in the presence. of an. alkylphosphoricacid (present, as a contaminant .. III traces) and a~-diketone, a phenomenon which has net beenreported so far. The work hitherto reported dealswith a combination of an acidic reagent and aneutral donor and synergism in the presence oftwo acidic and dissimilar reagents has been reportedhere for the first time. The extraction of indiumbv a mixture of di-2-ethylhexylphcsphoric acid(HD EHP) and ~-diketones like thenoyltrifluoro-acet~ne (HTTA), benzoyltrifluo~oacetone (HBFA)and dibenzoylmethane (HDBM) IS reported here.Materials and MethodsIndium, in the form of In1Hm, was obtained fromIsotope Division, BARC, and was assayed usingliquid GM detectors (Mis Electronics Corporationof India Ltd, Hyderabad). HITA and HDBM(Koch-Light) and HBFA (K & K) were used.HD2EHP (BDH, LR) was purified (purity> 99% )by the method of Peppard et al», Benzene (BDH,AR) was used as the diluent.Extraction experiments were carried out byequilibrating the aqueous phase containing indium,sodium perchlorate to keep the ionic strength (1·0)and perchloric acid to adjust the pH with an equalvolume of the organic phase containing the ex-tractants in a thermo stated mechanical shaker for734about 8 hr. Indium in the aqueous phase wasmeasured using a liquid GM detector. Indiumin the organic phase was stripped with an acidsolution and assaved, The pH of the aqueous'phase was measured using a Beckman expando-matic SS-2 pH meter.Results and DiscussionIndium-HD2EHP system - The extraction of in-dium by HD2EHP and the ~-dikctones alone wasstudied to assess the extent of extraction bv theindividual ligands. The extraction by ()-dike"tonesis negligible at pH <2 (refs. 1, 3). The extraction ofindium bv HD2EHP depends on the third power of[HD2EHPJ and inversely on [H+J. HD2EHP existsas a dimer in benzene and chloroform media as hasbeen reportcd='. The reaction can therefore bewritten asIn3++3[(HD2EHP)2JO~[In (HD2EHP .D2EHPhJo + 3H+ '" (1)The equilibrium constant given byK03= D[HJ3[HD2EHPJg ... (2)was calculated as 103•8 on the dimer molarity scaleand indicated HD2EHP to be a good extractantfor indium.Indinm-HD2EHP-HTT A system - The extractionof indium by a mixture of HD2EHP and HTTA wasstudied as a function of pH and concentrations ofHD2EHP and HTTA. Fig. 1 shows the plots oflog D vs pH, log[HD2EHPJ and 10g[HTTAJ. Theplot of log D vs pH had a slope of above 4 whichis higher than the expected value of 3. The twoother plots were linear with slope = 1·5. Thedecrease in the slope dependence of HD2EHPindicates the number of HD2EHP molecules asso-ciated with the extracted complex to be less thanthat in the parent complex. The two ligandsbehave as chelating agents and occupy two coordi-nation positions in the chelate se that in the presenceof both the ligands, a competition for the metalsite occurs resulting in the replacement of theHD2EHP dimer by HTTA for the formation ofSUDERSANAN & SUNDARAM: SYNERGISM IN THE EXTRACTION OF INDIUMIo ,o'rI!). 0O...Jo .7 ~/3 2//:o,,"p nA. x 103 F M1 2.96pH-0.8 0.0250.025 1.21.223I I I1.2 1.4 1.62.92.0 1.23.10pH2.1 - LOG[HD2EHP]-!..OG[TTAjFig. 1 - Plots of log D versus log [HD2EHPJ, log [TTA]and pHthe .mixcd chelate. It is interesting to note thatthe sum of HD2EHP and HTTA molecules in thechelate is 3' thereby satisfying the coordinationnumber. Due to the strong enolic character andability to form stabler complexes, one or two mole-cules of HTTA are present in the chelate.Indium-HD2EHP-HBFA system - The extractionof indium bv a mixture of HD.EHP and HBFAwas also st{;,died. Experiments -were carried outin a similar manner and the results are presentedin Fig. 2. The enhancement in the ~xtractionwas also observed in this case indicating the pheno-menon to be quite general. The increase wasslightly higher than in the case of HTTA thoughthe reagent extracted indium only at a higher pH.Three hydrogen ions arc involved in the extractionwhich depends on the second power of the con-centration of HD2EHP and on the first power ofthat of HBF A indicating the replacement of oneHBF A molecule per HD2EHP dimer in the chelate.Hence the overall reaction can be represented byEq. (3).In3++2[(HD2EHP)2Jo+[HBFAJo~[In(HD2EHP.D2EHP)2BFAJo+3H+ ... (3)Indium-HD2EHP-HDBM system - Extractionof indium by a mixture of HD2EHP and HDBM,which extracted only at a higher pH, was alsostudied. Fig. 3 gives the various plots of log Dvs pH and concentrations of the two extractants.Synergism was also observed in this case thoughto a lesser extent probably due to the wider dis-parity in the extractability of the individualligands.The results indicate the replacement of HD2EHPmolecules in the chelate by HDBM. Synergismin the presence of two dissimilar ligands appearsto be a general phenomenon.The ~-dik:::tones replaced the bulky HD2EHPdimer in the chelate and the stabilization appearsto be due to the greater asymmetry of the chargedistribution and reduced steric hindrance. Thisis borne out by the fact that the ~-diketones replacethe HD2EHP dimer although they do not them-selves extract indium. A similar phenomenon hasalso been observed in the chelates of some metalswith EDTA and NTAS. The number of replaced4~'" 103F1 3.102 2.863BFA pHM0.0251.00.010 1.0 I1.2 1.6 pH- LOG[8FA]2.1 -LOG[Ko2EHI»2.6 1. B2.9Fig. 2 - Plots of log D versus log [BFA], log [HD2EHPJand pHI11+0.8 2Ho2EHP oBM pH,,103F M2.86 0.052.86 1.170I!) 00...J-0'[Fig.o2 •1.0 1.4 1.8 pH1.6 1.2 - LOG[oBM]3 - Plots of log D versus log [DBM] and pHHD2EHP molecules increases in the order HDBM<HBFA<HTTA which is also the order of extract-abilitv of indium .. Thermodynamics of extraction - The extra stabi-hz~ tIOn. of the synergistic species studied here isquite high compared to that observed for mixed~-diketone chelatess and hence cannot be accountedfor on the basis of statistical theories or other ob-servations relating the stability of mixed chelateswith those of the individual ligands. Hence itwas thought worth while to investigate the thermo-dynamics of extraction process to assess the con-tr ibution of enthalpy and entropy factors to theextraction.The effect of temperature was studied in thecase of indium-HD2EHP-HBFA system in therange of 10Q to 50° at different concentrations ofHBF A or pH, keeping the concentration of HD EHPconstant.. The extraction by HD2EHP alon~ wasalso ~tudle.d at different temperatures. The resultsare given In Table 1 and Fig. 4 shows the plot oflog D vs liT.'The equilibrium constant for the extraction ofindium by a mixture of HD2EHP and HBFArepresented by Eq. (3) can be written asK12= Dsyn[H]3[HD2EHP]o2[HBFA]ii1 ••• (4)735INDIAN J. CHEM., VOL. 15A, AUGUST 1977TABLE 1 - EFFECT OF TEMPERATUREON THE EXTRACTIONOF INDIUMBY HD.EHP ANDBFA(HD.EHP = 2·69 x 10'sF)[BFA] pH log D log K* log Dsyn log K'· T l/TxlQ2x 102M °C1·0 1·06 0·11 4·07 0·09 4·65 22'2 3·3921·0 1·09 0·21 4·08 0·19 4·66 15·5 3·4781·0 1-07 0·00 3·93 -0·01 4·52 30'0 3·3001·0 1·07 -0·09 3·84 -0'10 4·42 37-0 3·2261·0 1·05 -0'17 3-82 -0·18 4·40 45'2 3·1471·0 0·98 -0·15 4·05 -0·18 4·62 17·0 3·4481·0 0·96 -0'25 4·01 -0·27 4·59 22·3 3·3931·0 0'97 -0'44 3·79 -0'46 4·37 36·5 3·2411·0 0·92 -0'44 3'94 -0'46 4·52 39·0 3·2051'6 0·93 0·05 4·20 0·Q4 4·79 15'5 3·4781·6 0·98 -0·07 3·93 -0,09 4·51 22·3 3·3931-6 0·91 -0·25 4-16 -0·26 4·75 36·3 3·2391·6 0·91 -0,33 3·88 -0·34 4·46 45·5 3·1501·05 -1·24 3·32 4·22 15·5 3·4781·07 -HO 3·40 4'30 15'5 3·4781-(19 -1·27 3-17 4·07 22·3 3'3931·08 -1·49 2·98 3·88 36·5 3·2411·00 -1'42 3·29 4·19 39·0 3·205•K = D[H]8[HD2EHP]-2[BFAJ-l for mixed and = D[H]8[HD,EHP]-a for simple complexes and K' = D[HJ8[HD.EHP':r."[BFA]-l for mixed and = D[H]I[HD.EHPli" for simple complexes.EFA pH• 102M1 04 o.sa2 1.0 1.073 1.0 0.974 i.e O.g,5 1.066 1.220.00.443coo...I 0.81.20.34, • 102TFig. 4 - Plots of log D versus lIT0.32 0.36The distribution ratio of the synergistic species,Dsyn, is nearly equal to the value due to the mixedchelate, this being much higher than that due toHD2EHP alone. The values of Dsyn, K03 and K12are given in Table 1.The values of 6.H, 6.G and 118 were calculatedfrom the variation of K12 with temperature, Sincethe thermodynamic equations are additive, the736TABLE2 - VALUESOF THERMODYNAMICPROPERTIESSystem log KM =sc -toR toSkcal moP kcal mol! e.u,Mixed chelate 4·6 6·4 5·6 3Simple chelate 4·0 5·5 5·6 0Synergistic species 0'6 0·9 0·0 3thermodynamic parameters for the synergistic re-action given by Eq. (5)[In(HD2EHP .D2EHP)3JO+ [HBF AJo~[In(HD2EHP.D2EHP)2BFAJo+[(HD2EHP)2Jo···(5)can be obtained by subtracting Eq. (3) fromEq. (1). The plots of lag D vs liT are all linearwith almost the same slope. The thermodynamicparameters as well as the equilibrium constantsfor the various species are given in Table 2. Thevalue of I1H was calculated as 5·6 + 0·2 kcal for boththe simple and mixed chelates. H-;nce the differencein the stability cannot be attributed to the heatof reaction. The heat of extraction accounts forthe stability of the chelate with HD2EHP alonewhereas the additional stabilization resulting in thereplacement of a bulky HD2EHP dimer by HBF Ais facilitated by reduced strain and steric hindrance.The entropy change for the formation of indium-HD2EHP chelate is almost zero. The factor whichstabilizes the chelate is the increase in the random-ness of the system (Eq. 6),In(H20W+3[HBFAJo~[In(BFA)81o+3H++6H20... (6}There is an increase in the number of moleculesand the increased randomness contributes to the-SUDERSANAN & SUNDARAM: SYNERGISM IN THE EXTRACTION OF INDIUMpositive entropy change thereby stabilizing thesystem. The formation of six-membered ring alsofavours a reduced strain on the metal-ligand bondthereby contributing to the positive entropy change.With bulky molecules like HD2EHP dimer, thepossibility of steric hindrance due to the arrange-ment of three chelate ligands around the metalion is more tending to destabilize the system. Inthe case of HD2EHP system these two factorsmay be mutually compensating each other so thatthe net stabilization is zero and the stability ofthe system is due to enthalpy changes. In the caseof the mixed chelate, the enthalpy contributionremains nearly constant but the strain on the systemis reduced by the replacement of HD2EHP dimerby a more compact and smaller BFA molecule whichwill therefore contribute to the entropy of thesystem. An asymmetry in the electronic distri-bution is also introduced favouring the formationof a stabler complex. On the other hand, thesystem is more likely to resemble. In(BF A)3 whenthe next higher complex [In(BFA)2HD2EHPJ isformed and the stability will be lower. Hence,the chelation proceeds only up to this stage andthe higher complex, if any, is not discernible.Infrared studies -- Infrared spectra were obtainedon a Perkin-Elmer infrared spectrophotometer usingCaF 2 cells of 0·1 mm thickness. The spectra forHD2EHP alone showed no absorption at 3500 crrr'!which is characteristic of -OH groups. Hencethe ligand is hydrogen-bonded and on the basisof the molecular weight measurements it can beconcluded that HD2EHP exists as a dimer+s,Infrared spectra of the indium mixed chelateswere obtained. In the case of In-HD2EHP-HTTAsystem, the concentrations were kept in the ratioof 1: 2 or 2: 1 to favour the formation of In(HD2-EHP.D2EHP)2 TTA and In(HD2EHP.D2EHP)(ITA)2mixed chelates. The spectrum of In-HD2EHPchelate is comparatively less complicated. Theabsorption due to "P=O of the ligand shifts from1225 cm-1 to 1200 crrr+ in the chelate indicatingthe coordination of the metal with the P=O groupand in fact, P = O.... M has been shown to absorbin this region in the case of TBP system",The spectrum for HTTA alone shows vC=Oand that due to the enolic group is almost absentwhereas in the case of metal-ITA spectrum thepeak at 1300 cm! is very pronounced. The spectradue to In-TTA is quite comparable to those of othermetal ions and shows the characteristic bands ofC = O-M at 1600, C = C at 1550 and C-O-Mat 1300 cm :'. The spectra of mixed chelates arequite complicated but the absorption peaks due tothe various groups are discernible. The spectrashows the coordination of metal ions through theC = O-M and C--O-M bonds of ITA andP=O-M group of HD2EHP. The relative absorp-tion of C=O-M and P=O-M groups changeswith the ratio of HD2EHP and TT A but no con-clusion can be drawn from these data regardingthe presence of two species since both the groupsabsorb at the same frequencies. Infrared studiesindicate the formation of a mixed chelate in whichboth HD2EHP and TT A molecules are bonded tothe metal ion, a conclusion which supports thesolvent extraction data.References1. SUDERSANAN, M. & SUNDARAM, A. K., Proc. IndianAcad. Sci., 75 (1972), 151; 78 (1973), 100; Curl'. Sci.,42 (1973), 88.2. PEPPARD, D. F., FERRARO, ]. R. & MASON, G. W., J.inorg. nucl. cu«, 7 (1958), 231-3. (a) STARY, ]. & HLADKY, E., Anal. Chim. Acta, 28 (1963),227; (b) STARY, ]., zt: Neorg. Khim., 4 (1959), 2412;(c) SCHWEITZER, G. K. & ANDERSON, M. M., J. inorg.nucl, Chem., 30 (1968), iosi.4. FERRARO, ]. R. & PEPPARD, D. F., Nucl. Sci. Engng,16 (1963), 389.5. ISRAELI, Y. J., Nature, Lond., 201 (1964). 389.6. SUDERSANAN, M. & SUNDARAM, A. K., Proc, IndianA cad. s«.. 82 (1975), 77.7. FERRARO, ]. R. & HEALY, T. V., J. inorg. nucl, cu«,24 (1962), 1463.737

Synergism in the Extraction of Indium by a Mixture of Di-2-ethylhexylphosphoric Acid & a β-Diketone

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Synergism in the Extraction of Indium by a Mixture of Di-2-ethylhexylphosphoric Acid & a β-Diketone

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