Janardhan, P. B.

Subbaiyan, M.

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IndianJournal of ChemistryVoL 15A, May 1977,pp.443-445ChromatographicSeparationof Te(IV) & Te(VI)M. SUBBAIYAN & P. B. JANARDHANDepartmentof Analytical Chemistry,University of Madras, A.C. CollegeCampus,Madras 600025Received 12 July 1976;revised 7 October 1976;accepted12 November 1976Valenceseparationof Te(IV)from Te(VI) by circularpaperchromato~raphyemployin~anumberof solventsystemsincludin~pyridine is described.Thedifferentialmi~rationsof thetwoionsareexplainedon thebasisof differentialsolubilization,complexationandprecipita-tion. Theseparatedionsareestimatedpolaro~rapbically.THE earlierworksI-9on theseparationof tellu-rium valencesmakeuse of mostly treatedpapersto studytheeffectof pH and electro-phoresisontelluriummigration. Adequateexplana-tion for the differentialmigrationof telluriumindifferentoxidationstatesis wantingin literature.The presentwork-aimsat devisingsimplemethodsof separationof tellurium valenceson untreatedWhatmanNo. 1 paper. Appropriateexplanationsareofferedfor the differentialmigrations.MaterialsandMethodsThe well-knownRutter's technique10of radialchromatographywasadoptedusingcircular(12 cmdiam.) WhatmanNo. 1 paper. The generalde-scriptionof the technique,precautionsto be ob-servedandthechoiceof eluentshavebeenpresentedin an earlierpublicationfromthis laboratoryll.Preparation of solutions- Solutions of 0·2Mstrengthof Te(IV) and Te(VI) werepreparedbydissolvingcalculatedamountsof analyticalgradesodiumtelluriteand orthotelluricacid respectivelyin 2N HCI.Known quantitiesof the two solutions weremixedandsubjectedto chromatographicseparation.Sprayreagent- A 5% stannouschloridesolutionin 1: 1 HCI was used for colour development.Both Te(IV) andTe(VI) gavebrownishblackcolourdue to reduction to the elementalstate. Thereagentis sensitiveto 0·6 (Jogof tellurium12.Thedevelopmentof colouris instantaneousin the caseof tellurite,whereaswith orthotellurate,the paperhadto be warmed.]}feasurementof R, values- The distancefromthe centreof thespot to the outerboundaryof thechromatographicband was measuredand relatedto thesolventfront to calculatetheR, values.ResultsandDiscussionDifferential migration- Differential migrationshavebeencarriedout with (a)simplesolventsand(b) mixedsolvents. -(a)SimPlesolvents- Polarsolventsuchaswater,methanol,ethyleneglycol and glycerolwere_noteffectivesincebothTe(IV) andTe(VI) migratedtothe sameextentin thesesolvents. Te(IV) movedin waferas a diffusedbanddueto gradualhydro-lysis in neutralmedium. Migrationis.seento.bepoorin solventsof lowerpolaritylike ethylalcohol,propanol,etc.. _ ;In acetoneandmethylethylketone,orthotelluricacid is insoluble13and so .doesnot migrate. Onthe other hand,tellurous.acid was solubilized'1:>Ythesesolventsandsomigratedappreciably(Table1);Resultsobtainedusing pyridine as solvent areinteresting,vide item 3 of Table 1._ Pyridine wasnot effectivein the migrationof eitherTe(IV)orTe(VI), if the chromatographiespot was driedbeforeelution. The non-migrationof Te(VI) hasbeenexplainedby GhoshM;azumdarand..t.edererGas due to the polymerizationof Te(VI) into aninsolublecomplex. On the other hand, whentheTABLE 1- CHROMATOGRAPHICBEHAVIOUROF Te(IV) ANDTe(VI) IN VARIOUSSOLVENTS .Eluents Rr valuesof/lBrTe(IV)Te(VI)SIMPLE SOLVENTS,"Acetone0·]2z ro0,72Methyl ethyl ketone5Se'55Pyridine (spot undried)zero,9·MIXED SOLVENTS Conc. HCl (35%, wt/v)·751 02Fo m c acid (90%, wt/v)' 7' 8. · 1Aq. ammoniaor m thyl90·705amine (25%, w /v) Ethanol-water (80:20)6666n-Propanol-wate (80:20)r· 0-5-water (80:20)4,Etha ol-conc.HCl (90:10),837l conc.HCI, 44 *4-(90:10) n-Butanol-conc.HCI; 1Amyl alcohol-conc.HCI68Pyridine-cone.HCI (90:10)Thioglyc l i cid-ethyl1 0cet t r -b tanolor aceto eor ether(10:90) 1·01: 1 solutionof 10% aq. ,84.0·16i ur a ( t/v) d 1 %.aq. nitric acid (v/v)INDIAN J. CHEM., VOL. 15A, MAY 1977elutio was done without drying the spots, Te(VI)rnigraed with an Rr 0·92whereasTe(IV) did notmigra e at all, possibly due to the p:-ecipitationoftellur s acid as Te02 (ref. 14). Dry orthotelluricacid, 2Te02(OH)4is also not soluble in pyridine.Its a ua-complex, H2[Te02(OH)4(H20)2] on theother and, is solubilized and migratesin interestingshap~ as a number of islands looking like moondigits. These interesting shapes can be explainedas fol ws:In t e presenceof water, orthotelluric acid existsas a aqua-complex formed through hydrogenbondig. The aqua-moiety of the complex beingpolar, 'is attracted towards pyridine and in fact getslinked with pyridine through the latter's lone pair.This 1ads to an orientation of the complex withthe ater molecules directed towards pyridine.The peed of migration of the aqua-complex isslowe' than that of the eluent pyridine. As thethin and of tellurium aqua-complex enlargesat atardy 'space,it experiencesincreasing thrust of thefaster moving pyridine from behind with the result,the c tinuous band breaks and forms small islands.Inside the islands, the tellurium occupiesthe interiorwith he hydrogen-bondedwater moleculesencircl-ing th tellurium and facing the pyridine all around.Why hould the shapeof the island be invariably amoon digit with the concavity up? This may bedue t the fact that when the two flanks of eachisland are being constantly draggedforward by thefaster moving pyridine, and when the telluriumaqua- omplex itself being tardy in its motion lagsbehin , the islands can assumeno other shape butof a lOon-digit.(b) fiXed solvents- Te(VI) migrated faster thanTe(I in cone. HCl (35%, wt/v) and formic acid(90% wt/v), showing appreciable separation (Table1). e(VI) is more polar in its complexes thanTe(IV and this accounts for its faster migration inpolar olvents. Tl).eorder of migration was reversedin th. case of aqueous ammonia (25%,wt/v) andmeth 1 amine (25%, wt/v). This is becauseTe(IV)forms a soluble complex with ammonia15and theamine whereas Te(VI) does noP6 and hence thelatter does not migrate. The observedR, 0·70 forTe(VI, against the expected zero, is to be attri-buted,to the presenceof water in these eluents.Sep rations achievedusingethanol-water,n-propa-nol-w. ter and pyridine-water mixtures, (Table 1)are at ributed to the correct adjustmentof polarityof the.eluentsso as to help the migration of the morepolar Te(VI) as comparedto Te(IV).In kohol-acid mixtures, the faster migratioo;nofTe(I\ is ascribedto its existenceas TeCl4 (ref. 17,18) w ich by virtue of a common ion, gets solubi-lized .y HCI and migrates faster (Table 1).Mig ational behaviour in pyridine-HCl mixturedeseres special mention. Pyridine hydrochloridemove slower than pyridine, setting up a distinctboun ary betweenthe pure solvent and its hydro-chlori e. Te(IV) was found to move invariably atthe yridine hydrochloride front. A significantobser ation was that Te(IV) always lay submergedin th pyridine hydrochloride region. It is there-fore i ferred that Te(IV) was solubilized by pyri-dine ydrochloride only, and not by pyridine.Te(IV) and pyridine seemto have affinity for HCl,which acts as a liaison betweenpyridine and TeC14.SelectivecomPlexation- Yet another method triedfor the separation of Te(IV) and Te(VI) was selec-tive complexation chromatography. A reagentwhich will complex preferentially with one of thetwo valencesis used. If now an eluent which is aspecific solvent for the complex is used, the com-plexed ion alone would migrate leaving behind theother. Even if the eluents were to solubilize boththe complexed and the uncomplexedions, in allp-obability the complexedion being heavier wouldmigrate slower and get isolated.Thioglycollic acid (TGA) can act as a reducingagent and a complexing agent. However, a 10%solution of TGA in oxygen-donor solvents behavesas a complexingagent rather than a reducingagent.In this dilute solution, it combines with Te(IV) inpreference to Te(VI) (ref. 19). The complex soformed migrates to the solvent front (Table 1)leaving behind uncomplexedTe(VI). Good separa-tion of the two ions was obtained using ethylacetate, amyl acetate, butanol, acetone and ether,each containing not more than 10% TGA.Thiourea is another selective complexing agentand it gives an yellow complexwith Te(IV) but notwith Te(VI) at room temperature20,21.Complexa-tion increasesthe covalent characterwith the resultthe Te(IV) thiourea complex moves slower thanTe(VI) in polar solvents like water and dilute acids(Table 1).Selectiveprecipitation- This technique consistsin precipitating one of the two ions during migra-tion, p:-eferablyat the central spot, while solubiliz-ing and migrating the other outwards. Eluentsemployed were binary mixtures of water-aliphaticalcoholsor water-pyridine. Organic solventsexert asalting out effect on aqueous solutions. With theexceptionof methanol,the alcohols like ethanol andpropanol gave satisfactory separations.The good separation of Te(IV) and Te(VI) ionsobtained by the use of pyridine-water (90: 10) is aperfect case of p:-ecipitation chromatography. Theelution in this case was carried out without dryingthe spot for reasonsmentionedearlier. Te(IV) gotprecipitated as Te02 at the central spot aided bythe salting out effect exercised by the pyridine.At the same time Te(VI) formed an aqua-complexwith the water of the eluent mixture. This aqua-complex was solubilized by pyridine via its lonepair and so it migrated with the pyridine boundarywith R, 0,95 and got separated.Quantitativeassessmentof separations- Quantita-tive evaluationwascarriedout polarographically22,23.Te(IV) and Te(VI) bands on the chromatogramswere marked out with the help of duplicate chro-matogramsrun simultaneouslyunderidentical condi-tions and sprayed. The marked out filter paperbands were then cut out and extracted with 20 mlof 1% HCI and washed with 5 ml of water. Incasessuch as thioglycollic acid where the ions werereduced to the elemental state on the chromato-gram, the filter paper bands were boiled with 10 mlof 20% HN03 which oxidizes Teo to Te(IV) andextracted. The solution was neutralized partiallywith ammonia.- --- -------- --~~- .~..SUBBAIYAN & }ANARDHAN: CHROMATOGRAPHICSEPARATION OF Te(IV) & Te(VI)TABLE 2- POLAROGRAPHICESTIMATIONOF Te(IV) AND Te(VI) AFTER SEPARATION[Te(IV) and Te(VI) spotted: 76,56lLgeach]Eluents Te as Te(IV)Estimated*(lLg)Te as Te(VI)Estimated*(lLg)Te(VI)Te(IV) + Te(VI)(%)x lOOtCone. HCI (35%) 78-4+1·8474·2-2,3648,63Formic acid (90%)7-30'78,92'350'52Aq. ammonia(25%)4 81 7-6,0 9cetone·15 ·06n-Pr pano!-water(80:20),6921.-06Py id -water (80:20)'l-conc.HC! (90:10)·6 71 4on .HCI (90:10)2510% solution of thiourea5932Butanol-TGA (90:1 )4 8, 8*Averageof four estimations.tRedox ratio: 50% =no reductionor oxidation; Above or below 50% indicatesoxidation or reductionrespectively.The estimationswerecarriedout with a PO 3Polariter radiometer(Copenhagen).Molar ammo-nium chloridesolutionbufferedwith ammoniatopH 8·5 was used as the supportingelectrolyte.The solutionwasdeoxygenatedwith nitrogenandafew dropsof 0·1% gelatinwereaddedto suppressmaxima. Te(IV) and Te(VI) gave well-definedreductionwavesat E1/2 -0·62 and -1,2 V respec-tively. Working graphswere preparedfor boththe ions by plottingthe heightsof the curvesofdiffusioncurrentvs concentrationsof the ions inthe rangeof 40-100 {log/100ml. The resultsarepresentedin Table 2.References1. AKIRA MURATA, J. chem.Soc. Japan, 78 (1957), 57;78 (1957),520.2. GRASSINI,G. & LEDERER, M., J. Chromatog.,2 (1959),326.3. POONIA,N. S.,J. chem.Edn, 43(1966),423;44(1967),477.4. VESELEY, F., SMIROUS,F. & VEPREK-SISKA, J., Chem.Listy, 49 (1955),1661;Chem.Abstr., 50 (1956),729h.5. GHOSHMAZUMDAR,A. S. & LEDERER,M., J. inorg.nucl.Chem.,3 (1957),379.{).ANNA SCHNEER& MARIA ORDOGH,J. Chromatog.,4(1960),319.7. PLUCHET,E. & LEDERER,M., J. Chromatog.,3 (1960),290.8. GoPAL, N. G. S. & FRAPART,P., Int. J. aPP1.radiat.,Isotopes,17 (1966),129;Anal. Abstr., 14 (1967),6107.9. ZAITSEV,V. M., GUSEL'NIKOV,V. S. & MAKHOMALKINA,S. M., Radiokhimiya, 11 (1969), 352; Anal. Abstr.,19 (1970),1231.10. RUTTER, L., Nature, Lond., 161 (1948),435; Analyst.75 (1950),37.11. PAUL, A. & JANARDHAN,P. B., Bull. chem.Soc.Japan,40 (1967),1131.12. FEIGL, F., Spot tests in inorganic analysis (Elsevier,New York), 1958,350.13. DURRANT,P. J. & DURRANT,B., Introductionto advancedinorganicchemistry(Longmans,London), 1962,887.14. JILEK, A. & KOTA, J., Colin Czech.chem.Commun.,6(1934),398; Chem.Abstr., 29 (1935),13588•15. VICTOR LENHER & EDWARD WOLESENSKY, J. Am.chem.Soc.,35 (1913),722.16. HORNER,H. J. & GUY WILLIAM LEONARD(Jr), J. Am.chem.Soc., 74 (1952),3694.17. KASARNOWSKY,Z. anorg.allgem.Chem.,128 (1923),28;cited by Schuhmann, R., J. Am. chern. Soc., 47(1925),356.18. LEDERER,M., Microchim.Acta, (1956),43.19. KJRKBRIGHT, G. F. & NG, W. K., Anal. chim. Acta,35 (1966),116.20. JILEK, A. & VRESTAL,J., Chem.Zvesti,7 (1953),33.21. JIELSCH, E. & GIEFER, L., Z. anal. Chem.,145 (1955),347; 155 (1957),401.22. LINGANE, J. J. & NIEDRACH,L. W., J. Am. chern.SQc.,70 (1948),4115;71 (1949),196.23. ELINOR NORTON,STOENNER,R. W. & MEDALIA, A. r.•J. Am. chem.Soc., 75 (1953),1827.

Chromatographic Separation of Te(IV) & Te(VI)

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Chromatographic Separation of Te(IV) & Te(VI)

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