Stability constants of glycerato complexes of cadmium and
lead were determined by the polarographic method. Measurements
were performed in buffer solutions of sod1um salt of DL-glyceDic
acid. The concentration of the glyceric aoid in the buffer solutions
was constant: 0.0 7 M for cadmium, and 0.05 NI for lead. The ionic
strenght of solutions was 2 and -it was kept constant by m e ans of
sodium perchlorate . The following cumulative stability constants
were obta;ined: Cadmium: Bi = 40, B2 = 130, B3 = 340, B = 2.10.
Lead: [3 1 = 340, B2 = 5.7 X 10 3, Ba = 2.8 X 10 3, B4 = 4.8 X 10 3 

B. Topuzovski

I. Filipović

English

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CCA-526 C R 0 A T I CA C H E M I C A A C T A 4 0 (1 9 6 8) 257 545.33 :546.48 :546.815 Note Polarographic Determination of Stability Constants of Glycerato Complexes of Cadmium and Lead B. Topuzovski and I. Filipovic Institute of Inorganic and Analytical Chemistry, University of Zagreb, and Chemical Institute, Faculty of Science, University of Skopje, Macedonia, Y11goslavia Received June 24, 1968 Stability constants of glycerato complexes of cadmium and lead were determined by the polarographic method. Measurements were performed in buffer solutions of sod1um salt of DL-glyceDic acid. The concentration of the glyceric aoid in the buffer solutions was constant: 0.07 M for cadmium, and 0.05 NI for lead. The ionic strenght of solutions was 2 and -it was kept constant by means of sodium perchlorate. The following cumulative stability constants were obta;ined: Cadmium: Bi = 40, B2 = 130, B3 = 340, B = 2.10. Lead: [3 1 = 340, B2 = 5.7 X 103, Ba = 2.8 X 103, B4 = 4.8 X 103• Literatu re data about the investigation of metal glycerato complexes are very scarce1 • However, the investigation of m etal glycerato complexes from the point of view of the chemistry of complex compounds is interesting not only because of the fact that glyceric acid is biologically important, but also in order to obtain a closer insight into the influence of the hydroxyl group in monocarboxylic acids, or their anions, on the composition and stability of the corresponding complexes2• Therefore the determination of the stability constants of glycerato complexes of cadmium and lead was performed by the polarographic met hod. Buffer solutions with constant limiting concentration of glyceric acid were used, at which the hydrolysis of cadmium and lead glycerato ·complexes does not yet occur2•3 : 0.07 M for cadmium, and 0.05 M for lead. The ionic strength of the solutions was 2 and it was k ept constant by means of sodium perchlorate. EXPERIMENTAL Polarographic measurements were made on the polarograph Polaviter P04 Radiometer ,in the way described in a previous paper4 • A-11 half-wave potentials are given with respect to the calomel electrode with a saturated solution of sodium chlorlde. All measurements were carDied out under constant temperature of 25 ± 0.1° C. The concentration of cadmium and lead in invesUgated solutions was 0.5 mM. By the addition of sodium perchlorate the ionic strength o.f the solutions was kept at a constant value of 2. The values m'i" t'I• of the capillary employed at the half-wave potentials of lead and cadmium in the buffer solutions with the ·concentration of sodium glycerate of 0.01 M were: 2.420 for lead, and 2.411 for cadmium. The buffer solutions were prepared from 65°/o DL-glyceric acid Fluka, purum. For that purpose the saponification of glyceric acid with a small excess of sodium hydroxyde was performed by hean~ng on a water bath far 15 minutes (in order to destroy the lactons present). The excess of sodium hydroxide was then determined by potentiomekic titration. From the alkaline solution of sodium glycerate thus obtained, buffer solutions were prepared by addition of the required quantity of 258 B. TOPUZOVSKI AND I. FILIPOVIC perchloric acid, so that the concentration of the liberated glyceric acid was constant: 0.07 M in cadmium solutions, and 0.05 M in lead solutions. At such concentrations of glyceric aoid in the buffer no hydrolysis of ~complexes ocurred in the solutions of sodium glycerate in the concentration range from 0.01 to 1.8 M2, 3• The half-wave potentials of cadmium and lead in the buffer solutions of glycerate were corrected to zero concentration of glyceric acid2,3• The half-wave potentials of the »free« ions of cadmium and lead were determined in slightly acidic solutions of sodium perchlorate (2111) by extrapolation to zero concentration of perchloric acid. RESULTS AND DISCUSSION Tables I and II represent the results of measurements and give cumulative (Bi) and stepwise (Ki) stability constants determined by the graphic method of DeFord and Hume5• The extrapolated values for the cumulative stability constants were checked to give the best fit by the method of successive approximations6• The confidence limits of the extrapolated constants Bi deduced from the dissipation of the experimental points depending on the precision of the half-wave potential measurements (± 1 to 2 mV) are within ± 10°/o. In Table III the obtained values for stability constants of monoligand (K1} glycerato complexes are compared with those of glycolato8 and lactato2 com-plexes, which were also determined by the polarographic method under analogous experimental conditions. It is seen that the order of stability of monoligand complexes as measured by K 1 is : glycolate <lactate< glycerate. It is evident that the stability of glycerato complexes is not determined by [L] M 0 0.01 0.02 0.03 0.04 0.06 0.08 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.60 1.80 -0.5540 -0.5592 -0.5617 - 0.5645 - 0.5664 - 0.5699 -0.5732 - 0.5771 - 0.5893 - 0.5980 - 0.6046 -0.6122 -0.6172 - 0.6222 - 0.6263 -0.6303 - 0.6346 -0.6366 -0.6405 -0.6435 -0.6464 - 0.6510 -0.6552 id ~tA 4.00 3.92 3.77 3.77 3.68 3.59 3.56 3.64 3.47 3.28 3.00 3.15 3.04 3.00 2.86 2.80 2.83 2.46 2.59 2.54 2.52 2.33 2.13 TABLE I Cadmium Glycerate Solutions I Fo ([L]) I Fi ([L]) I F 2 (;[L]) I Fa ([L]) I F4 (i[L]) 1.42 1 1.84 2.29 2.72 3.66 4.78 6.34 17.6 36 66 113 173 260 376 524 724 978 1260 1621 2045 3170 4814 -42.2 42.0 42.8 43.0 44.4 47.2 53.4 81.3 116 162 225 288 370 468 580 723 879 1049 1246 1460 1981 2674 S1 = 40 Ki = 40 - - -- - -- - -- - -- - -- - -- - -134 - -206 383 208 255 416 254 305 437 243 369 473 267 413 471 219• 471 487 210 535 507 208 601 523 212 683 553 215 763 575 214 841 593 210 928 614 211 1015 632 208 1213 677 211 1464 741 223 S2 = 130 ~a = 340 S4 = 210 K~ = 3.3 Ka = 2.6 K4 = 0.6 STABILITY CONSTANTS OF COMPLEXES 25!) the degree of basic character of the ligand (increasing in the order: glycerate < < glycolate < lactate), but by the presence of another hydroxyl group. The higher complex stability with the dihydroxymonocarboxylate ions is probably due to a certain, though very small, chelate effect. [L] M 0 0.01 0.02 0.03 0.04 0.06 0.08 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.60 1.80 Ei12 v -0,3670 -0.3868 -0.3953 -0.4017 - 0.4063 - 0.4136 - 0.4196 - 0.4236 - 0.4400 - 0.4491 - 0.4573 - 0.4638 - 0.4685 -0.4733 -0.4772 -0.4813 - 0.4845 - 0.4878 - 0.4908 -0.4936 - 0.4964 -0.5013 -0.5055 id µA 4.15 3.94 3.77 3.89 3.83 3.67 3.67 3.44 3.47 3.15 3.23 3.22 3.06 3.03 2.97 2.88 2.75 2.67 2.62 2.55 2.53 2.38 2.22 TABLE II Lead Glycerate Solutions I Fo ([L]) I F i ([L]) I F 2 (1[L]) I F3 ([L]) Fdi[L]) I - - - - -4.73 373 - - -9.38 419 - - -15.1 469 - - -,21.8 519 - - -40.2 653 - - -64.1 789 5614 - -93.5 925 5854 - -333 1662 6610 4550 -749 2494 7179 4930 -1389 3470 7825 5312 -2303 4604 8530 5660 -3504 5838 9156 5760 4933 5164 7375 10051 6216 488(} 7115 8892 10690 6240 4300 10098 11219 12088 7099 4777 13605 13604 13264 7564 4764 17969 16334 14541 8037 4761 23300 19416 15897 8497 4748 27997 21535 16320 8170 4131 37327 26662 18810 9364 4689 58213 36383 22527 10517 4823 86778 48209 26594 11608 4893 ' I Bi = 340 I B2 = 5700 I B3 = 2800 I B4 = 4800 K1 = 340 K 2 = 17 K 3 = 0.5 K 4= 1.7 I TABLE III Stability Constants of Monoligand Complexes (K1) Metal H + ion Cd2+ Pb2+ Ligand Log K11,1 Glycerate 40 340 3.517 Glycolate 268 808 3.712 Lactate 213 1403 3.739 REFERENCES 1. R. K. Cannan and A. K i br i ck, J. Am. Chem. Soc. 60 (1938) 2314. 2. I. Fi 1 i p o v i c, I. Pi 1 j a c, A. M e d v e d , S. S a vi c, A . B u j a k , B . B a c h -- Drag u tin o v d c, and B. Mayer, Croat. Chem. Acta 40 (1968) 131. 3. I. Fi 1 i po vi c, I. Pi 1 j a c, A . Med v e d, S. S a v i c, A . B u j a k , B . B a c h -Drag u tin o vi c, and B . M: ayer, Proceedings of the IVth Internatio;u;,l Con-gress on Polarography, Prague 1966, p . 24. '260 B. TOPUZOVSKI AND I. FILIPOVI C ·4. I. Fi 1 i po vi c, A. B u j a k, H. M a r a c, R. N o v a k, and V. Vu k i c e vi c, Croat. Chem. Acta 32 (1960) 219. 5. D . D. De Ford and D. N. Hume, J . Am . Chem. Soc. 73 (1951) 5321. 6. P. Pap off and M. Ca 1 i um i, Gazzetta Chim. Ital. 84 (1954) 1006. 7. Stability Constants, Compiled by L. G. Si 11 en and A. E. Marte 1. The Chemical Society, London 1964. -8. Unpublished results from this Institute. IZVOD Polarografsko odredivanje konstanata stabilnosti glicerato-kompleksa kadmiuma i plumbuma B. Topuzovski i I. Filipovic Odredene su konstante stabilnosti gHcerato-kompleksa kadmiuma i plumbuma polarograskom metodom. Mjerenja su izvrsena u puferskim otopinama natr:ijumove soli DL-glicerinske kiseline. Koncentracija glicerinske kiseline u puferu bila je kon-stantna •i to 0,07 M kod kadmiuma i 0,05 M kod plumbuma. Ionska jakost otopina bila je 2 i odrfavana je konstantnom pomocu natrium-perklorata. Dobivene su ove vrijednosti kumulativnih konstanata stabilnosti: Kadmium: Bi = 40, f32 = 130, B3 = 340, B4 ·= 210. Plumbum: (h = 340, 132 = 5.7 X 103, B3 = 2.8 X 103, B4 = 4.8 X 103 • INSTITUT ZA ANORGA NSKU I ANALITICKU KEMIJU SVEUCIL ISTA U ZAGREBU I KEMIJSKI INSTITUT PRIRODNO-MATEMATICKOG FAKULTETA UNIVERZITETA U SKOP.TU Primljeno 24. lipnja 1968. 

Polarographic Determination of Stability Constants of Glycerato Complexes of Cadmium and Lead

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