The stability constants of copper, lead , and cadmiwn lactate
complexes have been d etermined by the polarographic method in
water solutions of a constant ionic strength 2. The examinations
were carried out in the lactate concentration range up to 2 M

I. Filipović

J . S. Savić

Hrčak - Portal of scientific journals of Croatia

CR 0 AT IC A CHEMIC A ACT A 37 (1965) 91 CCA-365 545.33 :547.469 Original Scientific Paper Polarographic Investigations of Lactato Complexes of Copper, Lead, Cadmium, and Indium J . S. Savic* and I. Filipovic Laboratory of Inorganic Chemi stry, Faculty of Technology, University of Zagreb, and L aboratory of Analytical Chemistry, Faculty of Science, Univer sity of Sarajevo, Yugoslavia Received January 6, 1965 The stability constants of copper, lead, and cadmiwn lactate complexes have been determined by the polarographic method in water solutions of a constant ionic strength 2. The examinations were carried out in the lactate concentration range up to 2 M. The following values of cumulative costants were obtained: Copper: Bi = 330, B2 = 1.1 X 104, B3 = 2.9 X 104, B4 = 5 X 103, Bs = l.5 X104. Lead: Bi = 75, B2 = 660, B3 = 1350, B4 = 1450. Cadmium: Bi = 30, B2 = 35, B3 = 540, B4 = so, Bs = 300. Thus far, only few investigations of laotato complexes o f metal ions have been carried out. fa the literature 1•2 there can be fouITTd only data about oopper1 and zinc2·3 lactato complexes, which were irnvestigated :by the spectrophoto-metric or potentiometric method. For this r eason the following mvestigatiom of copper, lead, cadmium and indium lactato complexes has been carried out. The polarographic method o.f i!Ilvest1ga-tion was applied and the stability constants ·of copper, lead amd cad:miuim were · eva1lua1ted by the method of DeFord and Hume4, as described in a prev.ious .paper.5 The calculation of the s1tability constants of ·indium lactat0 complexes was not poissihle, ~si:nce the half-wave potential of the free indium ion could not be obtained experi-mentally6 because ,of irreversibility of the electrode process in the ·absence ·Of the la.ctate. The tha11ium (I), zi!Ilc and bismuth lactato complexes were also investiigated, but their .stability constants could not be determined, because of polarographic irreversibiMy of the electrode process with zinc aind bismuth and because of the rather small shift of the half-wave potential (about 5 mV) with thallium (I). EXPERIMENTAL The measurements were performed with a Radiometer P03 i)olarograph. The potential drop across the potentiometer of the polarograph was as low as 500 mV, which was attained by switcMng o.f corresponding resistances .in front of and behind the potentiometer. This potential drop was determ1ned by a compen-sation potentiometer to the nearest± 1 mV and was adjusted before each measu-rement with a Weston standard cell. In this way a maximum accuracy of the • Part o.f the thesis presented to the University o.f Zagreb, 1963, in partial fulfilment of the requirements for the degree of Doctor of Chemistry (Ph. D.). 92 J. S. SAVIC AND >r. FILIPOVIC half-wave potential determinations of ± 1 mV (± 2 mV for -indium) was achieved. The polarographic cell and other equipment did not differ from that described in the previous papers. The determination of the diffusion current, the half-wave potential and the diffusion current constant was performed in the same way as described previously5, All half-wave potentials are given with respect to the calomel electrode with a saturated solution of sodium chloride. The solutions were prepared from chemically pure reagents. Lactic acid »Analar« of The British Drug Houses Ltd. was used. The concentration of copper, lead and cadmium (as nitrate) was 0.6 mM, whereas that of indium (as perchlorate) was 0.4 mM. The concentration of the lactate was varied from O to 2 M. The lactate was obtained by addition of a known excess of sodium hydroxide to the solUtion of lactic acid. In this way even condensatio1n products of the lactic acid were converted to the lactate. From such an alkaline solution of a lactate, the solution of the lactate buffer of a constant ionic strength 2 was prepared by addition of a corresponding amount of perchloric acid and sodium perchlorate. In order to obtain the lowest possible concentration of lactate ion, in solutions containing only lactic acid the dissociation of the acid was suppressed by addition of a known amount of perchloric acid.' In such solutions and in buffer solutions with a low concentration of sodium lactate, the concentration of the lactate ioln was calcu-lated from the dissociation constant o.f the lactic acid. The concentration of the lactic acid in buffer solutions was constant?, i.e. iiI1 solutions of lead and cadmium complexes it was 2 M, whereas with cap:per and indium it was 0.1 M. Under such experimental conditions, the electrode processes of these ions were polarographi-cally reversible in the entire investigated concentration range of the lactate ion. Ln buffer solutions with a higher concentration of lactic acid (2 M) and a low content of lactate ion, the half-wave potentials of copper became more negative with decreasing lactate ion concentration, instead of more positive as usual. The described experimental conditions made possible the determina1Jion of the half-wave potential of the »free« metal ions, by extrapolation to zero lactate con-centrations, buL only for copper, lead and cadmium. For ndium this was not possible, since the curve representing the relation o.f the half-wave potential against lactate concentration was too steep. Besides, the electro'de process of indium in solutions without the complex forming substance is irreversible6. It is interesting to note that the electrode reaction of indium was pofarographi-cally revers~ble only in buffer solutions which did not contain more than 0.1 moles/I of the free lactic acid. The pH value of such solutions was between 1 and 5. In buffers with a higher lactic acid concentration, the electrode processes were irrever-sible. An analogous behaviour, i.e. irreversible reduction of ·ilndium, was found by D. Cozzi and S. VivarelliB in solutions with pH less than 1. No polarngraphic maxima were observed, probably because of the capillary activity of the lactic acid. Accordingly, no gelatine was added to the solutions. All measurements were carried out under constant temperature of 25 ± o.1oc. RESULTS AND DISCUSSION The composition of the complexes aind their cumulative 1stability cons-taints have been determilned by tthe graphic method od DeFord and Hume4•5• The extraipolated values fOO' the cUimlula1tive stability constants were checked to give the best fat, by the method of successive appr.oximatiom.s, as recom-mended ,by P. Pa,poff aITTd M. Calium.i10• The c001fidence hmi.ts of the extra-polaited constaITTts, deduced from the diissipaition of he expedmentaJ prnints depending on the precision of the half-wave potential measurements11, are within± 100/o for lead lactato complexes, am:d ± 150/o for cadmium and copper lactato complexes. The results are shown in Tables I-IV. It i·s mterestilng to mention that the aimount .of lactic acid m the buffer has a d.i·stilnct ilnfluence on the diffusion currents .of all ilnvesitigated cations and particularly ·Oill the mdi:um iOill. The polarographic wave of indium even diisaippears completely at greater com.cootrations of lactic acid. ':Che concein.-tration of lactic acid a:t which the wave disappea:rs depends on the con-{L] M 0.000 0.011 0.016 0.021 0.03 0.04 0.06 0.08 0.10 0.15 0.20 0.25 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1,.60 1.70 1.80 1.90 2.00 Ei/2 v +0.043 +0.021 +0.015 +0.011 +0.005 -0.001 -0.010 -0.017 -0.021 -0.032 -0.041 -0.047 -0.053 -0.061 -0.069 -0.076 -0.080 -0.086 -0.090 -0.094 -0.098 -0.102 -0.106 -0.109 -0.112 -0.115 -0.119 -0.121 -0.124 -0.127 I F01[L] 3.20 -3,.0(i 6.06 3.04 9.37 3.02 12.7 2.98 20.7 2.97 32.7 2.94 68.9 2.89 116 2.87 165 2.86 391 2.82 787 2.79 1253 2.75 2031 2.69 4129 2.65 7334 2.56 12997 2.52 19357 2.50 29133 2.43 41555 2.38 60213 2.35 84528 2.32 11.3 x 104 2.28 15..4 x 104 2.23 19.9 x 104 2.22 25.9 x 104 2.16 33.7 x 104 2.11 46.3 x 104 2.08 56.8 x 104 2.01 71.8 x 104 1.98 94.2 x 104 TABLE I Copper Lactate Solutions F1([L]) F2([L]) Fa~!L]) F4([L]) Fs([L]) -----459 11727 ---523 12062 ---557 10809 ---658 10933 ---792 11550 ---1131 13350 ---1438 13850 ---1637 13070 ---2597 15113 ---3932 18010 ---5009 18716 30864 --6768 21460 34867 --10319 24972 34930 --14666 28672 35344 --21660 35550 40917 --27651 39030 40043 15775 15393 36415 45106 42632 17040 15050 46171 50964 44404 17115 13461 60212 59882 48882 19882 14882 76842 69556 52233 21121 14655 93907 77981 55817 22347 14456 11.9 x 104 91042 61571 25055 15427 14.2 x 104 10.1 x 104 64536 25383 14559 17.3 x 104 U.5 X 104 69314 26876 14584 21.0 x 104 13.1 x 104 75207 28879 14924 27.2 x 104 16.0 x 104 87681 34518 17363 31.5 x 104 17.5 x 104 91110 34505 16391 37.8 x 104 19.9 x 104 98879 36778 16.725 47.1 x 104 23.5 x 104 11.2 x 104 41601 18300 ~! = 330 ~2 = l.1Xl04 I ~3 = 2.9X104 I ~4 = 5Xl03 I ~5 = 1.5Xl04 'ti 0 t"" > ~ 0 @ > 'ti ::r: ..... n ..... z ~ Ul >-3 s > >-3 0 z Ul 0 "'J t"" > n >-3 > >-3 0 n 0 ::::: 'ti t"" t'l ~ t'l Ul co w 94 1[L] M 0.0000 0.010 0.017 0.019 0.022 0.026 0.029 0.037 0.046 0.064 0.083 0.103 0.152 0.201 0.251 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1,.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 E1/2 v -0.363 -0.370 -0.373 -0.374 -0.376 -0.378 -0.379 -0.382 -0.385 -0.389 -0.394 -0.397 -0.405 -0.412 -0.418 -0.423 - 0.431 -0.438 -0.445 -0.450 -0.455 -0.459 -0.464 -0.467 -0.470 -0.473 -0.476 -0.479 -0.481 -0.484 -0.487 -0.488 -0.491 I 2.71 2.61 2.59 2.58 2.56 2.54 2.52 2.49 2.47 2.44 2.42 2.40 2.36 2.32 2.29 2.25 2.19 2.14 2.09 2.05 1 99 . 1.95 1.93 l.89 1.85 1.82 1.78 1.74 1.70 1.68 1.63 1.61 1.57 J. S. SAVIC AND I. FILIPOVIC TABLE II Lead Lactate Solutions - - - - -1.83 83.4 - - -2.32 77.5 - - -2.56 82.0 - - -3.01 91.3 - - -3.43 93.6 - - -3.89 99.7 - - -4.90 105 - - -6.05 110 - - -8.78 122 727 - -12.5 139 772 - -16.7 153 757 - -31.9 203 844 - -56.1 274 990 1650 -85.1 335 1037 1506 -131 434 1195 1783 1443 262 651 1441 1952 1505 451 900 1650 1980 1260 766 1275 2000 2233 1472 1176 1679 2291 2330 1400 1771 2212 2672 2515 1456 2568 2853 3086 2695 1494 3701 3700 3625 2965 1615 4778 4342 3879 2926 1433 6443 5368 4411 3126 1480 8295 6380 4850 3223 1441 10766 7689 5439 3413 1473 13390 8926 5900 3493 1428 16793 10495 6512 i 3657 1442 20420 12011 7021 3742 1407 26038 14465 7994 ~' 4074 I 1513 29996 15787 8308 I 4025 1408 ! 37536 18767 9383 r 4361 1505 I 131 = 75 1 132 = 660 I fl3 = 1350 I 134. = 1450 ~~~-'-~~~--'--~~--'-~~~---'--~~~-centratiOiil of the laotate ,ill. the buffer. The greater the amount o.f lactate, the greater the decrea1se of the height of the polamgraphic wave 01f mdiiUl!Il with mcrea<Si.!n.g lactic aoi:d co1nce1I11Jra:tion. This effect is oertainly caused by the chal!lge of viscosity12 o.f the ibuffer resulting from the 1iJncrea1sing co111ceflltra:tio111 of lactic acid. However, the observed di1sappeairance of the polaTog1raiphic wave of indium ion, when greater amounts of the lactic acid are p;resent in the buffer, is prnsuma:bly due ;to its capillary activity, i.e. to the cha111ge of the double layer structure on the ,surface :of the droppii.!n.g mercury electrode8• The l,actato complexes of cadirnrum, lead, aind copper are weak com-plexes, ais are complexes of these ions w1th other monocarboxyla.te ligands5,13,l4. In the table given below, the stahility constants (~ 1) of lactato complexes of cadmium, lead, anid copper are presented along wjth characteristics which influence the stability of complexes such as: the ionic potential (z/r or z2/r, [L] M 0.0000 0.010 0.017 0.019 0.022 0.026 0.029 0.037 0.046 0.064 0.083 0.103 0.152 0,201 0.251 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 i. fo 1.20 l.3b 1.40 1.50 1.60 l.7Q 1.80 1..90 2.00. POLAROGRAPHIC INVESTIGATI ONS OF LACTATO COMPLEXES 95 -0.538 2.50 - 0.542 2.46 -0.544 2.45 -0.544 2.45 -0.545 2.44 -0.546 2.43 -0.546 2.42 -0.548 2.40 -0.549 2.38 -0.552 2.36 -0.555 2.33 -0.558 2.31 -0.564 2.26 -0.570 2.22 -0.575 2.18 -0.580 2.14 -0.588 2.08 -0.595 2.02 - 0.602 1.98 -0.607 1.94 -0.614 1.90 - 0.618 1.86 -0.622 1.82 - 0.627 1.78 -0.631 1.75 -0.634 1.70 -0.638 1.68 - 0.640 1.65 -0.644 1.61 -0.647 1.58 -0.649 1.55 -0.652 1.52 -0.655 1.4!! TABLE III Cadmium Lactate Solutions - - -1.33 33.6 -1.59 35.0 -1.67 35.3 -1.74 33.7 -1.89 34.4 -1.94 32.6 -2.19 32.1 56.7 2.52 33.0 65.2 3.19 34.1 64.1 4.04 36.7 80.2 4.99 38.8 85.3 8.43 48.9 124 13.3 61.1 155 20.6 78.0 191 29.9 96.3 221 59.5 146 291 106 210 359 180 297 446 289 412 545 478 596 707 683 757 808 999 998 968 1418 1288 1144 1968 1639 1341 2658 2044 1549 3605 2575 1817 4472 2980 1967 6001 3750 2325 7627 4486 2621 9360 5199 2872 12325 6486 3398 15391 7695 3832 -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -545 - -488 - -587 - -596 - -622 - -620 - -639 247 -649 218 276 684 240 267 729 270 271 840 375 368 859 354 304 933 393 313 1008 425 314 1088 457 314 1165 481 308 1273 523 316 1288 499 279 1431 557 298 1521 577 292 1576 575 275 1770 647 298 1898 679 299 1 ~1 = 30 1 ~2 = 35 1 ~3 = 540/ ~4 = 80 I ~5 = 300 i.e. t he ion cha:rige d.i:viided by iion radius), the ionization potmtial In (Me<n-l) + -+ Men+ + e-, i.e. the electron affinity) a;nd the rpolarizability (a): cct2+ Pb2+ cu2+ z/r(15) (z/A) 2.06 1.67 2.78 !n(16) (eV) 16.9 15.0 20.2 a. x 1024<17) (cm3) 1.03 4.32 0.70 ~1 30 75 280 It is obvious that in the case of cadmium and copper .the ionic potential and the ionizahon potential are the .principal facto:rs c01I1trolling the stability of complexes (Cd< Cu). With a large ion such as the lead ion, its .pol.ariza-bility is decisive, and acoordmgly ·the stability of the lead lactato complexes is ]ntermediate between the stabilities of cadmium anq copper: Cd< Pb< Cu. 96 J. S. SAVIC AND I. FILIPOVIC TABLE IV Indium Lactate Solutions [L] Ei/2 I M v 0.011 -0.546 4.03 0.016 -0.553 4.02 0.021 -0.560 3.99 0:03 -0.569 3.98 0.04 -0.576 3.96 0:06 -0.587 3.94 0.08 -0.595 3.91 0.10 -0.602 3.89 0.15 -0.614 3.83 0:20 -0.624 3.79 0:25 -0.632 3.14 0:30 -0.638 3.70 0.40 -0:648 3.63 0.50 -0.656 3.55 o·.60 -0.663 3.47 0.70 - 0.668 3.43 0.80 - 0.673 3.33 0.90 -0.678 3.27 1,.00 - 0.682 3.23 1.10 -0.685 3.14 1.20 -0.690 3.09 1.30 -0.693 3.03 1.40 -0.697 2.97 1.50 - 0.699 2.91 1.60 -0.702 2.84 1.70 -0.705 2.80 1.80 -0.708 2.76 1.90 -0.710 2.70 2.00 -0.713 2.65 This series is completely ·in accordance with the .series for other cOlffiplexes, g:iven by Irv:img aind Williams18, Mel.lair and Ma.ley19, Prue20 and Feder,s·en.21 • Therefore, these imve1stigation r esults confirm the cOIIlclusion that the ;ioni-zation potential a:nd the polarizaibility of the central ion ought to b e considered as principally respons~ble for a greater or 1smaller stabilhty of the complexes with mo:noca·rbo}!:ylate ions. With respect to ligands, the s tability of complexes depends ·On their basi-city (i.e. on the electron dono·r character). As the b aisicity of the monocair-boxylate ligands .is increasing in the series: formate <lactate< acetate< prn:pio111ate, the staibility o.f the 001r responding lead complexes is .imcreasing acoordingly5 : Bi = 13, 75, 150, 170. Cadmium complexes13 are sh:owirrlg the same sequence for the first three ligands. Copper lacta1to complexes are more stable, probably due t·o the pn:1sence of the hydroxyl group in the lactate iOIIl. However, it is .rather dif:flicult to judge if lactate ion acts as chelate group in inves1tigated systems. The fact tha·t t he maximum of stability is achieved in the third complex 1may perhaps be . 1taken as evide111ce of a tendency for ohelate formation. Acknowledgement. One of the authors (J. S. S.) expresses his thanks to the Republic Fund for Scientific Work of the SR of Bosnia and Herzegovina for the financial aid in this work POLAROGRAPHIC INVESTIGATIONS OF LACTATO COMPLEXES 97 .'REFERENCES 1. M. B ob t e I s k i aind I. B a r - Gad d a, Bull. Soc. Chim. France (1953) 276. 2. R. K. Cannan and A. Ki brick, J. Am. Chem. Soc. 60 (1938) 2314. 3. C. W. D av i es and C. B. M o n k, Trans. Faraday Soc. 50 (1954) 132. 4. D. D.. D e Ford and D. N. Hume, J. Am. Chem. Soc. 73 (1951) 5321. 5. I. F i I i p o vi c, A. B u j a k, H. M a r a c, R. N o v a k, and V. V u k i c e v i c, Croat. Chem. Acta 32 (1960) 219. 6. E . D. M nor h e ad and W. M. Ma c Nevi n, Anal. Chem. 34 (1962) 269. 7. I. Fi Hp o vi c and I. Pi I j a c, Croat. Chem. Acta 36 (1964) 181. 8. D. C oz z i and S. Viv a re 11 i, Z. Elektrochem., Ber. Bunsenges. physik. Chem. 58 (1964) 907; 57 (1953) 408. 9. Unpublished results. 10. P. P ap off and M. C a I i u mi, Gazzetta Chim. Ital. 84 (1954) 1006. 11. J . S. Savi c, Diss., Zagreb, 1963. 12. I. M. Ko Ith off and J. J. Ling an e, Polarography. Vol. I. Interscience Publishers, New York, 1952., p. 56. 13. A. Med v e d and I. Fi Ii po vi c, Croat. Chem. Acta 35 (1963) 51. 14. I. Filipovic, I. Piljac, Z. Crnic, M. Radulovic, and Dj. Valente-k o vi c, Croat. Chem. Acta 33 (1961) 45. 15. R. P arsons, Handbook of Electrochemical Constants, Butterworths Scientific Publications, Lnndon, 1959., table II. 16. Lando It - B or n stein, Zahlenwerte un-d Funktinnen. Band I, Teil I. Sprin-ger Verlag, Berlin, 1950., S. 211-212. 17,. B. E. C o n w a y, Electrochemical D ata. Elsevier PublishLng Company, Amster-dam, 1952., ip. 26. 18. H . Irwin g and R. J. P. W i 11 i am ·S, J. Chem. Soc. (1953) 3192. 19. D. P . Me 11 or and L. E. Ma I e y, Nature 159 (1947) 370; 161 (1948) 436. 20. J. E . Prue, J. Am. Chem. Soc. 74 (1952) 2331. 21. K. J. Peders en, Acta Chem. Scand. 2 (1948) 385. IZVOD Polarografska istrazivanja laktato-kompleksa bakra, olova, kadmija i indija J. s. Savic i I. Filipovic Polarografskom metodom DeForda i Humea odredeni su sastav i konstante stabilnosti bakarnih, olovnih i kadmijevih laktato-kompleksa. Otopi.ne su bile ionske jakosti 2, a koncentracija laktata varirana je do 2 M uz konstantnu kon-centraciju mlijecne kiseline u tamponskoj otopi.ni (0,1 M kod bakra i indija i 2 M kod 10Iova i kadmija). Dobivene su ove kumulativ.ne konstante stabilno·sti: bakar: Bi = 330, B2 = u x 104, Ba = 2.9 x 104, B4 = 5 x 10a, B5 = 1.5 x 104 olovo: Bi = 75, B2 = 660, [1a = 1350, B4 = 1450; kadmij: Bi = 30, B2 = 35, Ba = 540, B4 = 80, B5 = 300. Konstante stabilnosti ~ndijevih laktato kompleksa nisu se mogle odrediti zbog ireverzibilnosti elektrodne reakcije u otop~nama indija koje ne sadde stvaraoca kompleksa. ZA VOD ZA ANORGANSKU KEMIJU TEHNOLOSKIFAKULTET ZAGREB i LABORATORIJ ZA ANALITICKU KEMIJU PRIRODNO-MATEMATSKI FAKULTET SARAJEVO Primlj e no 6. sijecnja 1965. 

Polarographic Investigations of Lactato Complexes of Copper, Lead, Cadmium, and Indium

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia