Kumaria, J. N.

Sandhu, R. S.

Sandhu, S. S.

English

NOPR

INDIAN J. CHEM., VOL. 14A, MAY 1976~ U. BAREFIELD, K., BUSH, D. H. & NELSON, S. M., Q. Rev../' . ch~m. Soc., 11 (1968), 457.~3. MASBIMA,M., Bull. ckem, Soc. Japan, 35 (1962), 332.~. NAGANO, K., KINOSHITA, H. & HIRAKAWA, A., ChBm.phaf'm. Bull. Japan, 1l (1964), 1207.J5. AGGARWAL,R. C. & NARANG, K. K., Indian J. cu«;14(A) (1976), 64.../1J AGGARWAL,R. C. & NARANG. K. K., Tnorg; chim. Acta,7 (1973). 651; Indian J. Chem .• 9 (1971), 1413.17. BACON,R. G. R. & LINDSAY,W. S., J. chem, Soc., (1958),1382.18. STRATTON,w. J. .t BUSH, D. H., J. Am. chem. Soc., 81(1960), 4834.Stability Constants & ThermodynamicFunctions of Mg(II), Ca(II), Sr(II), Ba(II)& Pb(lI) Complexes with Thiophene-2-carboxylic AcidS. S. SANDHU, R. S. SANDHU & J. N. KUMARIADepartment of Chemistry, Guru Nanak University, AmritsarReceived 12 August 1974; accepted 17 July 1975The proton-Ilgand stability constant of thiophene-l-carboxyllc acid and the stability constants of its 1 : 1complexes with Ma2-f, CaH, SrH, Ba2+ and Pb2+ havebeen determined in aq. medium (!L=O·2M) usinaCalvin-BJerrum pH titration techinique. The AGO,ABo and ASo of the complexes have also been calculatedusina Gibbs-Helmholtz equation.THE stability constants of the complexes ofthiophene-2-carboxylic acid with Mg2+, Ca2+,5r2+, Ba2+ and Pb2+ have been evaluated using theCalvin-Bjerrumt-s titration technique as modifiedby Irving-Rossotti". Thermodynamic parametersof the reactions have also been evaluated.All the chemicals used were of BDH (AR grade).The standard solutions of the ligand and the metalsalts were prepared in conductivity water. pH wasmeasured on a Digicord pH-meter. The ionic strengthwas kept constant by NaCIO. (l'OM) solution andthe titrations were carried out at 30°, 40° and 50°C.For each set of experiments following three tit rationswere performed:(a) Acid titration - HClO. (O'lM, 5 ml) +NaCIO. (l'OM, 9·5 ml) + conductivity water (35·5ml).(b) Reagent titration - HeIO. (O·lM, S ml) +NaCIQ. (1,0.'11, 9 ml) + Ligand (O'OSM, 10 ml) +conductivity water (26 ml).(c) Metal titration - HClO~ (O'IM, 5 ml) +NaCIO. (l·OM. 8·9 ml) + Ligand (0·05M, 10 ml) +metal solution (O·OIM, 5 ml) + conductivity water(21 ml).The initial volume of the solution was 50 ml ineach case. The plots of pH of the solution againstthe volume of alkali added were of the usual shapes.Proton-ligand and metal-ligand stability constants- The proton-ligand stability constant was obtained(Table 1) by Bjerrum half-integral method and alsoby point-wise calculation method at different pointsin the proton-ligand formation curve using Eq. (1)log KIf=PH+log 11,H/l-11,H ... (1)The values of log KIf at 30, 40 and 500 are 2'95,3·35 and 3·65 respectively.The metal-ligand stability constants (Table 1)were determined by Bjerrum half-integral methodsand also by point-wise calculation method from thecorresponding formation curves using Eq. (2).log Kl = PL-Iog (1-11,)/11, ... (2)Thermodynamic parameters - The values of overallchanges in free energy (AGO), enthalpy (AHO) andentropy (~SO) have been determined using the Gibbs-Helmholtz equation- (Table 1).In thiophene-2-carboxylic acid complexes 11,-valuesremain less than one indicating the formation of 1:1complexes. The data shows an increase in the valueof long K~ with increase in temperature. The valuesof log Kl are positive in all cases, and increase withincrease of temperature. The values of llGo forthe complexes become more negative indicating thatthe complex formation is a spontaneous process.The formation of all the complexes is an endothermicreaction and it explains the increase in the valuesof the formation constants with rise in temperature.The entropy change, ASo, accompanying theformation of complexes, is positive in all the cases.References1. CALVIN. M. & WILSON, K. W .• J. Am. chem, Soc., 67(1945). 2003.2. BJERRUM, J .. Metal amine formation in aqueous solution(P. Hasse & Son. Copenhagen), 1941, 298; Chem,~ Abstr .• 35 (1941), 6527.~. IRVING.H.M. & ROSSOTTI,H.S., J. client, Soc. (1954). 2904.4. YATSIMIRSKII. K. B. & VASI'L·Ev. V. P.• Instabilitycons/ants of complex compounds (D. Van Xostrand,)\cw'£orl,), 1960. 63.TABLE 1 -METAL-LIGAND STABILITY CONST.\NTSAND THERMODYNA~IICP~\RAMETERSOF THE COMPLEXESAT DIFFERENTTEMPERATURESlog Kl at -~Go (K joule/mole) ~Ho ~5°(K joule/ (joule/30° 40° 50° 30° 40° 50° mole) mole/40° degree)40°1'95 2·00 2·76 11·30 11'97 17·05 72-86 271'022·01 2·09 2·21 11·65 12'51 13·65 18'22 98·182·01 2·09 2·35 11·65 12-51 14'52 30·97 138'912'06 2·09 2-51 11'94 12'51 15'51 40·99 170·932'03 2-14 2·18 11·76 12-81 13'47 13'66 84'57Me talionMgf.fCat+'SrI+'Ba'+Pb2+366

Stability Constants & Thermodynamic Functions of Mg(II), Ca(II), Sr(II), Ba(II) & Pb(II) Complexes with Thiophene- 2-carboxylic Acid

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Stability Constants & Thermodynamic Functions of Mg(II), Ca(II), Sr(II), Ba(II) & Pb(II) Complexes with Thiophene- 2-carboxylic Acid

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