Gowda, B. T.

Mahadevappa, D. S.

English

NOPR

INDL\N J. CHDI., VOL. 1H, OCTOBER 1977Direct & Indirect Titrimetric Determinationsof Thiocyanate Ion in Metal Salts &Complexes with Dichloramine- T & SomeFurther Applications of Chloramine- TB. T. GOWDA & D. S. :\'lAHADEVAPPA*Department of Postgraduate Studies & Research in ChemistryUniversity of Mysore, Manasa Gangotri, Mysore 570006Received 27 December 1976; accepted 1 A pril1977Simple and accurate direct and indirect titration(visual and potentiometric) methods for the determi-nation of thiocyanate ion in metal salts and complexeswith chlorarnlne-T and dichloramtne-T in the presenceof sodium acetate and KBr have been developed. Theoxidation involves an eight-electron process. Amethodfor determining cyanide and thiocyanate ions inmixtures is also described.THE methods reported so far for the determina-tion of thiocyanate include the use of hypo-halite-, bromine", iodine", iodate+ and H202 (ref. 5).These involve mostly back titration proceduresand have a number of experimental restrictions.Although the reaction of chlorarnine-T with CKS-ion has been mentioned in litcraturc+? detailedstudies arc: lacking.The present communication reports a simplemethod for estimating thiocyanate ion in metalsalts and complexes by (i) a direct titration withchloramine-T (CAT) or dichloraniine-T (DCT) inthe presence of KEr, with a visual or potentiometricend-point and (ii) a back titration procedure. Aneight-electron change is observed under these condi-tions.Triply distilled water was used for preparingaqueous solutions. AR grade KCNS (E. Merck)was dried at 1500 and its puritv checked+, Metalthiocyanates, NaCNS, Cd(CNS)2' Zn(CNS)2'Ni(CNS)2.0·5H20, Ba(CNS)2.2H20, Pb(CNS)2'U02(CNS)2.3H20 and complexes K~Pb(CNS)6' K2Zn-(CNS)4.4H20, K2Cd(CNS)4·2H20, K4Ni(CNS)6.4H20and KU02(CNS)3.2H20 were prepared by standardmethods and recrystallized from aqueous solutionand their purity checked by elemental analyses.Solutions of the compounds (",,2 mg/ml) in wateror dilute acetic acid (only lead compounds) wereprepared. Preparation of standard CAT and DCI'solutions are described in earlier communications-vP.Approximately IN KBr and 20% sodium acetatesolutions were prepared. A Bajaj potentiometerwith a platinum indicator electrode and a referencecalomel electrode wer 3 used for potentiometrictitrations.Direct titration: Method (1) - A direct titrationof thiocyanate (salt or complex) with CAT or DCTwas found practicable in the presence of sodiumacetate and KBr (and acetic acid in titrations withCAT). Sodium acetate was found to catalyse theoxidation.----------*To whom communications are to be addressed.938To aliquots of thiocyanate solution were addedsodium acetate solution (5 ml), KBr solution (10ml) and CC14 (1 ml) ~glacial acetic acid (5 ml) intitrations with CAr. The solution was titrat-ed with CAT or ncr with stirring till theappearance of a faint yellow colour in CCl4 laver.Blank correction was found to be about 0,05- mlof O·llY oxidant. Potentiometric titration wasalso carried out for the determination of the end-point. A large potential jump of ",,300-500 mVwas noticed for the addition of 0·1 ml of O·INoxidant at the end-point.Method (2) - In this method the reductantsolution was added to a known volume of theoxidant containing KEr and CC14 (and glacialacetic acid in the case of CAT). The end-pointwas noted visually as well as potentiometrically(potential jump of ",,300-500 rnv at the end-point).Back titration method - The pH of the thiocyanatesolution was adjusted to any value between 1 and6. Aliquots of the solution were added to a knownvolume (""SO";, excess) of Q·IN CAT in an iodineflask and set aside for about 20 min in case of metalsalts and only for 5 min with thiocyanate com-plexes, shaking occasionally. Sulphuric acid (10ml, 2N) and potassium iodide solution (20°o, 10ml) were added and the reaction mixture titratedwith 0·12'1 sodium thiosulphate. A blank was runwith the same volume of CAT solution.Similar titration procedure was adopted withO'l}\' DCT in water or dil. acetic acid.The eight-electron stoichiometry observed indirect titration is shown in Eqs. (1-~~, assumingin situ liberation of bromine from KEr bv theoxidants. .RNCINa+2Bc+2H+--:;..RNH2--:-Na+~Cl--;-Br2 (1)RNC12+4Br-+2H+--:;..RNH2+2Cl-+2Br2 (2)where R=p-CH3C6H4S02.CNS-+4Br2+4H20--:;..SO:-+CNBr+8H++7Bc ... (3)Bromine cyanide formed could be quantita tivelvestimated by the iodometric method-", .The stoichiometry observed in the back titrationis indicated by Eq. (4).CNS-+4RNClNa (or 2RNC12)+5H20--:;..SO~-+2II+-+CNO--L4I~NH2 (or 21~KH2)+4Na+ (or 4H+) 1+Cl- ... (41The presence of CNO- ion in the reaction productswas detected by spot tests14,15. The sulphonamidewas detected by paper chromatography=.The results of analysis given in Table 1 showthe range of amounts of thiocyanate employedand the per cent error in the recovery. Each rang('covers the amounts present in 8-10 different aliquotsof t.he compound. For comparison the resultsobtained by the argcntometric method-s are alsoincluded in Table 1. It is seen that the maximumerror encountered in the present method is about0·5%.. Common anions such as sulphate, phosphate,nitrate and perchlorate and fluoride 0.0 not interferebut iodide ion interferes in direct titration andbron~ide .ion .in the back titration and N2H4 andcyanide IOn Interfere in both the tit rations.NOTESTABLE 1 - TITRIMETRIC DETER,lIN.-\TIO:-I OF THIOCYANATE WITH CAT AND DCI'Compound Range Error (%) (method-f) Back AgN03 Range Error (%) (method-2)studied titration method-" studied(mg) Visual Potentio- (mg) Visual Potentio-metric metricTITRATlOX wITH CATKCNS 1·02-102 38 0,00-0,49 0·00-0-49 0·00-0·24 0·00-0,59 1'39-111-12 0·00-0,50 0,00-0,36~aCNS 1·88-112·69 0·07-0·53 0·02-0·53 0'04-0'53 O'DO-O'27 H3-11 NO O·DO-O·4() O·DO-O·4()Cd(CKS), 1·80-108·00 0,00-0,55 0·00-0·56 0·13-0·55 0·00-0·60 1·60-127·84 0·00-0·25 0·00-0·31Ni(CNS!..0·5H2O 0·93-92·75 0·00-0'37 0·00-0·54 0·00-0'54 0'00-0'39 1·02-102·00 0-00-0'49 0·DO-O·53Pb(CKS). 2·00-100·16 0·00-0,50 000-0'55 0·00-0,50 0·00-0·50 1-13-112·98 0·00-0·49 0·15-0·44Zn(CNS), 1·56-120·74 0·00-0-51 0,00-0,32 0·03-0,32 0·00-0·58 1·27-126·90 0·02-0·47 0,00-0·39Ba(CNS) a- 2H,O 1·00-100·00 0·00-0-50 0-00-0'31 0·00-0'60 0·00-0·60 1·03-103·44 0,00-0,48 0,00-0,39UO,(CNS) a- 3H,O 2-41-120-72 0·00-0·25 0,00-0,58 0-00-0·48 0·41-1·03 1'36-135·69 0·00-052 0·00-0·52K,Zn(CNS) •. 4H2O 1·07-128·42 0,00-0,56 0·00-0·37 0·00-0,35 0'47-1·17 1,38-110,48 0·00-0,36 0·00-0·43K,Cd(CNS)4_2H,O 2,03-101,55 0,00-0,49 0·07-0·49 0·00-0,49 0·DO-l·08 2·83-113·12 0·17-0·53 0,00-0·35K.Ni(CNS) s-4H6O 2-04-101'SO 0'25-0·49 0·25-0·49 0,20-0·49 0-00-1'19 2·62-104·80 0,13-0·53 0·06-0·46K.Pb(CKS)6 203-101'35 0·10-0'50 0-20-0·50 0·00-0-50 0-28-0'74 1·46-116·96 0·DO-0·48 0,00-0'55KU02(CNSJs,2H2O 2·01-100·50 0·00-0'32 006-0'50 0·00-0·40 0·00-1·00 1·07-106·70 0·00-0-33 0·00-0·47TITRATION wITH DCI'KCKS 1·02-102·38 0·00-0-49 0·00-0·20 0·00-0·49 0,00-0·59 1·25-100·DO 0'00-0-48 0·00-0·4()NaCi\S 1'88-112·69 0·09-0·53 007-0'53 0-05-0-53 0·00-0'27 1,25-124,50 0·00-0·4() 0·00-0·48Cd(CKS), 1·80-108·00 0'00-0'44 0·00-0·44 0·11-0·55 0,00-0,60 1,76-122,85 0·00-0·51 0'00-0'52Ni(CKS)2·0·5H,O 0·93-92·75 0,00-0,54 0·00-0·54 0·00-0-54 0·00-0·39 1·22-122·00 0·00-0-41 0,00-0'33Pb(CNS). 2'00-100·16 0,00-0,50 0,00-0·50 0·00-0·50 0·00-0·50 0·99-118·41 0·10-0'51 0·00-0·28Zn(CNS), 1·56-124·74 0·00-0·42 0·00-0·58 0'00-0'51 0,00-0·58 1,39-111-52 0·11-0·43 0·14-0'39Ba(CNS)2·2H,O 1·00-100·00 0·00-0,60 0·00-0·50 0,00-0,60 0'00-0'60 1·86-111·75 0·00-0·4() 0·00-0·54UO,(CNS),.3 H,O 2·41-120·72 0'02-0-50 0·00-0·58 0'00-0-46 0,41-1,03 1'45-115'70 0,00-0,35 0,00-0,35K,Zn (CXS) •. 4H2O 1·07-128-42 0-00-0'47 0-00-0·47 0·00-0040 0-47-1-17 1·47-117·68 0'00-0'41 0·00-0·34K,Cd(CNSJ.,2H2O 2·03-101·55 0·02-0-49 0·10-0-49 0·00-0'37 0·00-1·08 1·49-119·44 0·00-0·35 0·00-0·49K.Ni(CNS) s .4H2O 1·02-101·80 0-00-0'49 0·00-0041 0·00-049 0'00-1'19 1·41-112-80 0,00-0,43 0·00-0'43K.Pb(CNS). 2-1)3-101'35 0'00-0'54 0·00-0·50 0·00-0·49 0,28-0,74 1·54-123·52 0·00-0·51 0,00-0'39KC02(C~Sh2H20 2· 01-100'50 0'20-0'51 0,00-0·50 0·00-0-50 0·00-1·00 2,25-112-65 0'09-0'44 0,00-0'44TABLE 2 - DIRECT TITRn!ETRIC DETERMr~ATlON OF THIOCYANATE AND CYANIDE Ioxs IX MIXTURES,WITH CHLORAMINE-T AND DrCHLoRAMINE-TVisual end-point Potentiometric end-pointTaken (mg) Founcl (mg) Taken (mg) Found (mg)CC\'S- CN- O;S- CK- CNS- 0;- CNS- CN-TITRATION WITH CAT0·92 0·92 0'92 0'92 0-92 0·92 0'92 0·922·29 2·29 2·30 2·30 2-30 2·30 2·29 2'314·58 4·58 4·58 4·62 4·60 4·60 4·58 4·629·20 9·20 9·20 9-17 9·20 9·20 9·16 9·2418·30 18·30 18040 18-35 18-40 18·4() 18·36 18·4136·70 36·70 36·80 36-69 36-80 36·80 36·87 36·5773·40 73·4() 73045 73·64 73·60 73-60 n52 73·5292·20 92-20 92·06 91·61 92-00 92·00 91·99 91·74TITRATION WITH DCT0·97 0·97 0·97 0·97 0·97 0·97 0·97 0·972·44 2·44 2·42 2·44 H2 H2 2·43 2·424·86 4·86 4·84 4·87 4·84 4'84 4·86 4·849·70 9·70 9·67 9·75 9·70 9·70 9·71 9·6819·45 19-45 19·42 19·36 19·40 19·40 19·39 19·4338·88 38·88 38·92 39·59 3890 38'90 38-85 38·7277-S0 77-80 77-62 77-58 77-60 77-60 77·55 77·7296·80 96·80 97·19 96'68 97·00 97·00 97·04 96·95Estimation oj thiocyanate and cyanide ions in amixture -- Since cyanide ion undergoes a two-'electron changeI2,I7 with CAT or DC-T, an aliquotof the oxidant solution (VI ml) of normality N wastitrated against a mixture of cyanide and thiocya-nate ions (Vi ml) as in method-Z. An aliquot (Vml) of the mixture "vas then taken and the cvanideion precipitated out as zinc cyanide by adding O·SMzinc sulphate. Thiocyanate in the filtrate wasdetermined by method-l (V2 mil. The amountsof CNS- (x, mg) and CN- (y, mg) in the reac-tion mixture are given by: x = 7·26NV2 and939INDIAN J. CHEM., VOL. 15A, OCTOBER 1977y=13N (V1- V2). Some typical results are given inTable 2.One of the authors (B.T.G.) acknowledges finan-cial assistance from the CSIR, New Delhi, in theform of a research fellowship.References1. TOMICEK,O. & JESEK, M., Colln Czech. chem. Commun.,10 (1938), 353.2. TREADWELL, F. P. & MAYR, C., Z. anorg. Chem., 92(1915), 127.3. Rupp, E. & SOHIED,A., s». dt. chem. Ges., 35 (1902). 2191;Arch. Pha1'm., 243 (1907), 460.4. HAMMOCK,E. W., BEAVON,D. & SWIFT, E. H., Analyt,cu«, 21 (1949), 970.5. WILSON, I. R & HARRIS, G. M., J. Am. chem. Soc., 82(1960), 4515.9406. SINGH,B. & SOOD,K. C., Anal. chim. Acta, 13 (1955), 30t.7. RAO, V. R S. & MURTHY, A. R V., Curro Sci., 30(1961), 176.8. KOMAROV'SKY, A. S., FILANOVA, W. F. & KORENMAN, I. M.,z. analyt, Chem., 96 (1934), 321.9. BISHOP, E. & JENNINGS, V. J., T'alanta, 9 (1962), 581.10. MORRIS,J. c.. SALAZAR,J. A. & WINEMAN, 1V1. A., J. Am.chem. Soc., 70 (1948), 2036.11. JACOB, T. J. & NAIR, c. G. R, T'alanta, 19 (1972), 347.12. MAHADEVAPPA,D. S. & GOWDA, B. T., T'alanta, 23(1976), 601.13 SCHULEK, E., Z. analyt, Chem., 62 (1923), 337.14. FEIGL, F., Spot tests in inorganic analysis (Elsevier,Amsterdam), 1958, 285.15. WERNER, E. A., J. chem. Soc., 123 (1923), 2577.16. VOGEL,A. I., A textbook of quantitative inorganic analysis(Longrnans, Green, London), 1961, 264.17. GOWDA,B. T. & MAHADEVAPPA,D. S., T'alanta, 24 (1977).325.

Direct & Indirect Titrimetric Determinations of Thiocyanate Ion in Metal Salts & Complexes with Dichloramine- T & Some Further Applications of Chloramine- T

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Direct & Indirect Titrimetric Determinations of Thiocyanate Ion in Metal Salts & Complexes with Dichloramine- T & Some Further Applications of Chloramine- T

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