Sudersanan, M.

Sundaram, A. K.

English

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INDIAN]. CHEM., VOL. 1SA, JUNE 1977grade solution (0·25%) in 0·25N H2S04 was pre-pared in conductivity water and stored in anambe-coloured bottle. Solutions of sulphosalicylicacid 0·1%) and KCNS (1M) were prepared fromanala grade reagents. All the other reagentsusedwere . f analar grade.he potentiometric assembly used consists ofOsaw Crompton potentiometer (Ambala, India),a sat rated calomel reference electrode, a brightplati m rod (0,2 mm diameter) as indicator elec-trode and a salt bridge filled with sat. solutions ofReI t ensurethe electricalcontact betweencalomelrefere ce electrodeand the titration vessel.Pot ntiometric titration method- To a portion(2-20 1)of thioglycollic acidsolution KeNS (1-2rol)and smic acid (0·3ml) solutions were added. Themixt re was diluted to SO ml and titrated withstan rd solution of Fe(III). The potentialsattainedstabl values immediately after the addition ofeach' ortion of the titrant exceptnearthe end-pointwher an interval of 2-3 min was needed.Vi ual titration method- In this method thetitra' on was carried out to the appearance ofredd' h-pink (in the caseof sulphosalicylic acid) orpale- ed (in the caseof KCNS) colour giving an in-terva of 20-30secafter the addition of each0,04mlporti n of Fe(III) solution near the end-point.E .ctof varying[acidJ- Best resultswereobtainedin th pH range 1-3. At higher [acid], the reactionwas low as indicated bv the slow attainment ofstabl potentials. At high~rpH hydrolysisof Fe(III)rend red the titration difficult.E ect of varying [thiocyanate]- The presenceof1-2 lof 1M KCNS enhancedthe speedof reactionnear he equivalencepoint where the inflection wasincre sed bv about 30 mV.E ect of varying [catalyst]- The presence of0'2-05 ml of 0·25% solution of osmic acid increa~edthe ate of reaction between Fe(III)-thiocyanatecom lex and thioglycollic acid 00 that U.e stablepote tials are attained within a period of 2-3 minnear the equivalencepoint.T e potential break at the equivalencepoint wasabo 170-180mV per 0·04 ml of O·lN Fe(III)solut·on. Thioglycollic acid in the range of 11-136mg ould be determined with Fe(III), with anaver ge error of 0·12%. Similar experimentswerecarrid out using O'OIN solutions of thioglycollicacid and Fe(III). In thesetitrations the optimumamo nt of osmic acid was found to be 0·1-0·3mlof O' % solution per SO ml of the titration mixtu"e.Thi lycollic acid in the range of 1·5-10mg couldbe etermined in centinormal solution with anaver ge error of 0·15%. Thioglycollic acid in therang s of 11-102 and 17-170 mg could also bedete mined visually with averageerrors of 0·27and0·13 ~ using thiocyanate and sulphosalicylic acidas i dicators, respectively.T epaleyellowcolourof osmium-thioglyccllicacidcom lex interferes in the visual detection of theend- oint if a higher concentrationof catalyst thanpres ribed is present.o e of us (K.R.R.) gratefully acknowledgestheDG ,New Delhi, for the award of a junior researchfello . ship.570References1. KARCHMER, ]. H., The analytical chemistryof sulphurand its compounds,Part I (Interscience Publishers,New York), 1970,478.2. ZYKA, ]. & BERKA, A., Chem.Abstr., 58 (1963), 7347h.3. NAIR, C. G. R. & JOSE, ]. J OCAB, Talanta, 12 (1965),1055.4. MAHADEVAPPA, D. S. & MADAIAH, M., Curro Sci., 42(1973),420.5. SUSEELA, B. SANT & BHARAT, R. SANT, Analyt. Chem.,31 (1959),1879.6. RozovA,N. D., Chem.Abstr., 74 (1971),15543£.7. GOPALA RAo, G. & MADHUSUDHANA RAo, V., Proc.natn. Inst. Sci., India, 12 (1946),217..8. STEEL, K. ]., J. Pharm. Pharmacal.,10 (1958),574.SolventExtraction& Ion-exchangeStudieson Cadmium& Thallium ComplexeswithGlycollic& LacticAcidsM. SUDERSANAN & A. K. SUNDARAMAnalvtical Chemistry DivisionBhabha Atomic ResearchCentre, Trombay, Bombay 400085Received20 ]VIa)'1976; accepted21 january 1977Complexesof cadmiumandthalliumwith glycollicandlacticacidshavebeenstudiedby themethodofsolventextractionusingpotassiumdinonylnaphthalenesulphonateas theauxiliaryli~and.An ion-exchan~estudy of cadmiumlactate,glycollateand fluoridecomplexeshas beenalso carriedout. The stabilityconstantswerecalculatedfor all thesystems.SOLVENT extraction has been widely usedfor thestudy of non-extractable complexes by themethod of competitive reactions],2. Ion-exchangehas also been employed for such studies. Incontinuation of our earlier work on indium com-plexes3, the results of our studies on cadmium andthallium complexeswith glycollic and lactic acidsare reported in this note.Cadmium as Cd1l5m and thallium as Tl204wereobtainf'd from the Isotope Division, BARe, and\\ere assayedusing GM detectors. Dinonylnaphtha-Jene sulphonic acid (R. T. Vanderbilt & Co.) wasestimatedby titration with sodium hydroxide4. Itspotassium salt was prepared by repeatedequilibra-tion with l'OM potassiumnitrate. Benzene (BDH,A K) was used as the diluent. Stock solutions ofglycolJic (Riedel De Haen) and lactic (Baker ana-lysed) acids were standardized by titration withsodium hydroxide. The ionic strength was main-tained at 0·5M by the addition of requisiteamountsof potassium nitrate.Extraction studies were carried out as describedearlier3 at 30°±1c. Experiments with cation ex-changer were performed using Dowex 50\V-X8(Baker analysed, 50-100 mesh) in potassium formby batch equilibration method.Solventextractionstudies- The extraction of cad-mium by the potassium salt of dinonylnaphthalenesulphonicacid (HDNNS) was studiedin the presenceand absenceof glycollic and lactic acids at differentpH. The concentrationof potassiumions was keptNO TES•.•(2)(Ofa:0I&.0.80,01&.0I!)...-0.80.5, ~-,.,,'11.02.0CADMIUM - GLYCOLLATE2 CADMIUM - LACTATEo SOLVET EXTRACTION...• ION EXCHANGE2.52.0a:o•••-1.01.01.1.0I!)o..• 0.01.5-LOG (xlFig. 1- Plots of log Fo versus log [X] for cadmiumglycollate (curve 1) and cadmium lactate (curve 2) complexesconstantat 0·50±O·OlM so that the distributionratio, Do, for cadmiumwouldbe constant.The concentrationsof the glycollateand lactateions werecalculatedfrom the pH of the solutionsandthepK valueof glycollicaciddeterminedfroma separateseriesof experimentsby thepH-titrationtechnique5. The pK values were found to be3·38±0·02 for glycollic acid and 3·52±0·02 forlactic acid at 30" at an ionic strengthof 0·5M(potassiumnitrate).T~e extractionmechanismcan be written assho nin Eq. (1),Cd2+f1-[(KDNNS),Jo~ [CdDNNSJo+2K+ ...(1)so ttat the extractiondependsinverselyon thesecod powerof theconcentrationof potassiumions.The distributionratio,Do, of cadmiumby KDNNScan e writtenas shownin Eq. (2).! [CdDNNSJoDo==1 N ---![CdJ+~[Cd(N03)n]I 1In! the presenceof glycollateion, X, the distri-butiqnratio, D, is givenbyD = N [CdDNN~loN ••.(3)[Cd]+~[Cd(N03)nJ+~[CdXnJ1 1It Ican~e shownfrom the aboveequationsthatC(t-1) =~~[XJ+~~[XJ2+ (4)wher~C =1+~;[N03]+~;[N03J2 (5)~~~nd ~~representthe stability constantsof~i~~rrfli.umglycollateand nitratecomplexesrespec-T e values of D, Do and DoD'l (or Fo) arepresntedin Table1. Theplot of logFo versuspXis a urve(Fig. 1)indicatingthepresenceof twoormar species.The data were analysedfor thestabiity constantsaki gi to accounther ported6valu~sforthenitratecomplexof cadmium(~~=0·62!TABLE 1- SOLVENT EXTRACTION DATA FORCADMIUM-GLYCOLLATE COMPLEXES([K+]=0·50M; Do =1·40)[GIyctcpHpx-log Dlog Foaci ] xlO,O'OS3·392·60-0' 2. -1,230·1-428, 7·740·131 559221 9 041,3480,-0, 0557·160· 20,7530261·6414563,6920, 844-359 8and~;=0,10). Thevaluesof logF 0 wereobtainedat differentconcentrationsof glycollateandlactate,ionsfromthesmoothcurve. The correctionfactor,C, wascalculatedat thesevaluesfrom the knownconcentrationsof potassiumnitrate. Eq. (4) wassolvedfor the individualstabilityconstantsby themethodof weightedleast-squaresusing BESM-6computer,the valuesobtainedbeing~~=37·4±1·6and ~;=560±28 for Cd-glycollatecomplexand~~=17·8±1·8 and ~;=114±17 for Cd-lactatecomplex.Ion-exchangestudies- HDNNS being a cationexchanger,it wasthoughtworthwhileto studythebehaviourof an analogous olid cation exchangerto comparethe advantagesof the two methods.ExperimentswerecarriedoutusingDowex50W-X8by batchequilibrationmethod,0·25g of the resinbeingusedfor eachexperiment.The resultsareshownin Fig. 1. The function,F 0' plottedas afunctionof pX wascalculatedfrom Eq. (6).Fo =DoD-l-l ,-~~aX]+~;[X]2+ (6)whereDo (77,7ml g'l) and D representhe distri-bution ratios of cadminmin the absence andpresenceof the ligand respectively.Do or D isdefinedasD =[~IJresin[ml of solut~o~] ...(7).M]solntion[g of reSlllIt can be seenfrom Fig. 1 that the data can besuperimposedonthoseobtainedbysolventextractionand henceno further analysisof the data forcalculatingthe stabilityconstantsis necessary.Cadmiumfluoride comPlexes- Complexesof cad-miumwithfluorideionwerestudiedby ion-exchangeusingDowex50W-X8in sodiumform. Experimentswere carried out in sodiumperchloratemedium.The pH of thesolutionswaskept in the range4-6where the dissociationof hydrogenfluoridewascomplete.The decreasein the distributionratiowas quite small but the variationof DoD-l as afunction of [fluoride]indicatedthe formationof571INDIAN J. CHEM., VOL. 15A, JUNE 1977weak fluoride complexes. From the plot oflog F against [X], functionF 1can be writtenasshow in Eq. (8).Fl = o/[X]=~{+~;[XJ+.••... (8)The ability constantswerecalculatedfroma plotof F against [X] and had the values,~{=3·1and ~=2·0. The values reportedhere can beregared as only approximatevaluessinceseveralotherfactorsarelikely to affectthe systemsin thecase f suchweakcomplexes.Th llium comPlexes- Complexesof thallium(I)with glycollic and lactic acids were studiedbysolvet extractionusing KDNNS as the auxiliaryligan. The extractionof thalliumwaspracticallyindepndent of pH at a concentrationof O·SM(potasiumions). Experimentswerecarriedout atvaryi g concentrationsof lactateor glycollateions,keepig the concentrationof HDNNS in potassiumform t a·GISM. The formationof weakcomplexesmake it necessaryto employhigh concentrationsof th complexingagentand hencethe concentra-tion f potassiumnitrate decreasesteadily. The572stability of thalliumnitrate complexesas well asthallium and potassiumglycollatecomplexeswillhave to be taken into account in these casesso that reliableand exact valuesof the stabilityconstantscannotbecalculated.Thesestudiesonlyindicatequalitativelythe formationof weakcom-plexesof thallium.The authorsthank Dr M. Sankar Das, Head,AnalyticalChemistryDivision,BARe, for his kindinterest.References1. SEKINE, T., Acta chem.scand., 19 (1965),1435,1+69,1476,1519.2. STARY, J., Solvent extractionchemistry,edited by D.Dyrssen, J. O. Liljenzin & J. Rydberg (North-Holland, Amsterdam),1967,1.3. SUDERSANAN, M. & SUNDARAM, A. K, Proc. IndianAcad. Sci., 75 (1972),151; Curro Sci., 42 (1973),88.4. KHOPKAR, P. K. & NARAYANANKUTTY, P., ]. inorg.nucl. Chem.,30 (1968),1957.5. CHABEREK, S. & ~IARTELL, A. E., ]. Am. chem.Soc.,74(1952),5052.6. CHIANG, H. C., Hong Kong Baptist Call. ]., 11 (1964),99; quotedby Saraiya,S. C. & Sundaram,A. K.,BARC Report No. 410, 1969.1"1

Solvent Extraction & Ion-exchange Studies on Cadmium & Thallium Complexes with Glycollic & Lactic Acids

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Solvent Extraction & Ion-exchange Studies on Cadmium & Thallium Complexes with Glycollic & Lactic Acids

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