Journal of the Serbian Chemical Society Vol 28 1963 (Ex Glasnik

This is a reproduction of a library book that was digitized by Google as part of an ongoing effort to preserve the information in books and make it universally accessible. http://books.google.com SRPSKO HEMIJSKO DRUSTVO (BEOGRAD) BULLETIN OF THE CHEMICAL SOCIETY Belgrade (Glasnik Hemijskog drustva — Beograd) Vol. 28, No. 1, 1963. Editor: MILOS MLADENOV1C Editorial Board : DELlC. D., DESPlC. A., DIZDAR, Z., DIMITRIJEVlC. DJ.. KONCAR.DJURDJEVlC, S., LEKO, A.. MIUC, M„ MLADENOVlC, M., MIHAILOVlC, M., MlCOVlC, V., RADOSAV- LJEVlC S., RASAJSKI, S„ STEFANOVlC. DJ., TUTUNDZlC, P.. HOROVIC, A., CELAP, M. Published by SRPSKO HEMIJSKO DRUSTVO (BEOGRAD) 1 96 3. Published pursuant to an agreement with the Department of Commerce and the National Science Foundation, Washington, D. C, by the NOLIT Publishing House, Terazije 27/11, Belgrade, Yugoslavia 1 9 64. Translated by ZORICA STOJADINOVlC Edited by DAVID TORNQUIST Printed in Beogradski Graficki Zavod, Belgrade [IL480 CONTENTS Page V. Vajgand and T. Pastor: Derivative Polarographic Titration of Bases in Glacial Acetic Acid in the Presence of Antimony or Quinhydrone Electrodes — — 5 A. Despid and Dj. Kosanovid: A Contribution to Methacrylacetone Studies. II. Physical Properties of the Monomer — — — — — — — — — — — — 13 M. Celap, T. Jan j id and D. Radanovic: Semiquantitative Determination of Small Amounts of Mercury, Palladium, Lead, Copper, Cadmium, Uranium, Iron, and Zinc by Precipita tion Chromatography on Paper — — — — — — — — 21 A. Stojiljkovid, M. Stefanovid, and R. Tasovac: Condensation Reactions of 2-Thiothiazolidine-4-One (Rhodanine) with Aromatic N, N-Bisamides in the Presence of Boron Trifluoride Etherate — — — — — — — — — — — — — 27 Dj. Stefanovid, S. Mladenovid, A. Milovanovid, and M. Stefanovid: Reactions of Aromatic Bisamides — — — — — — — — — 31 M. Conkid: Examination of Belite Cement Clinker — — — — — — — 37 69 548 AA A 30 GLASNIK HEMUSKOG DRUSTVA, Vol. 28, No. 1, 1963, pp. 1—7. DERIVATIVE POLAROGRAPHIC TITRATION OF BASES IN GLACIAL ACETIC ACID IN THE PRESENCE OF ANTIMONY OR QUINHYDRONE ELECTRODES by V. VAJGAND and T. PASTOR In our earlier report we presented a method by which it is possible to determine bases in acetic acid by derivative polarographic titration, using quinhydrone electrodes. Our work was later extended to the investigation of the behavior and properties of other electrodes in derivative polarographic and biamperometric (dead-stop) titrations. In this report we present the results obtained by the use of antimony electrodes in derivative polarographic titration. Antimony electrodes often used for pH determinations and for potentiometric titration of acids and bases in an aqueous medium, are sometimes also used for titrations in non-aqueous solvents. More detailed investigations have been made in neutral and alkaline solvents while TomiSek and Heyrovsky (2) and Shkodin and Karkuzaki (3) have also carried out potentiometric titrations in glacial acetic acid. The first two authors have established that the potential at antimony electrodes is more positive in acetic acid than in water and that it is necessary to remove water from acetic acid by the addition of acetic anhydride. Shkodin and Karkuzaki have noticed that at the antimony electrodes the potential is established rapidly and that the titration curve of strong bases (pyridine, sodium acetate) obtained in their presence is more symmetrical than the curves obtained in the presence of other electrodes. By examining the influence of water and acetic anhydride on the jump in potential at the end-point of the reaction of very weak bases we have established that in the presence of 0.5 to 1% of water the potential jump vanishes completely, the first 10 — 20% of anhydride has the greatest effect on the potential jump, while the highest jumps are obtained with 85 — 95% anhydride. By experimenting with bimetallic electrode systems in a nonaqueous medium Novak (4) has established that in acetic acid containing 30% acetic anhydride the best results are obtained with the antimony-graphite electrode system (graphite has a constant potential. Enoki and Mirisaka (5) have applied antimony electrodes in the derivative polarographic titration of acids and bases in aqueous 6 and alcoholic solutions, and Bishop and Short (6,7,8) in an aqueous solution. The latter authors have studied in great detail the processes at the electrodes and various influences on the change in potential during titration. It is evident from this that antimony electrodes have so far been used mostly for titration in an aqueous medium and less frequently in a non-aqueous medium. In this work we have studied the possibility of their application in derivative polarographic titration of organic bases and alkaline salts of organic acids in acetic acid with perchloric acid. We have also compared the properties of antimony and quinhydrone electrodes and the results obtained by these electrodes. EXPERIMENTAL The apparatus used was described in our earlier paper (1). Two "Radiometer" antimony electrodes were employed. Glajial acetic acid p.a. "Fluka" mixed with acetic anhydride, p.a. "Kemika", was used as solvent. For the titration of hydrochloride of organic bases a 3% solution of "Kemika" mercuric acetate was added to the solution. For the titration of liquid amines (triethylamine. triheptylamine, etc) the solution was prepared in a normal volumetric flask by weighing the specified amounts of amines on an analytical balance. From this solution weighed volumes were used for titration. The potentiometric titration was carried out in the presence of a glass electrode connected to a reference Hg/Hg2 (CH,COO), electrode (9). A fiber-type saturated calomel electrode was used for measuring the anode and cathode potentials. The 0.1N HC104 solution was standardized by a sodium acetate solution prepared by dissolving suitable amounts of sodium carbonate, p.a. "Merck", previously dried at 270° C. Antimony electrodes are suitable in the titration of tertiary amines and alkaline salts of organic acids. The end-point of the reaction is marked by the maximum in potential difference obtained during titration. The peak of this maximum depends on the strength of the base titrated. Thus, for example in titrating diethylaniline (K = 4.5-10-8 in water) in a mixture of acetic acid and its anhydride (1:1) a change in potential difference of about 140mV per 0.1 ml of the 0.1 N HC104 solution added was obtained at the equivalence point while for caffein, under the same conditions (K = 4.1-10~14 in water) and the same amount of the titration agent, the change in potential difference at the equivalence point was only 15 mV. The sharpness of the end-point of the reaction also depends on the composition of the solvent used, as illustrated by the following examples: In the titration of brucine with acetic acid and its anhydride mixed in the proportion 6 : 1 the potential difference obtained at the equivalence point was 50 mV for 0.1 ml of 0.1 N HC104, whereas if the proportion between the acid and anhydride was 1 : 1 the difference was about 120 mV. A similar relation was also found in other titrated systems. 7 8 To study the titration curves we measured the change in potential at the anode and cathode against a saturated calomel electrode. These curves have a bilogarithmic form characteristic of potentiometric titrations at constant current (Fig. 1). The end-point of the reaction calculated from the change in the anode potential occurred somewhat earlier than the equivalence point, while the end-point calculated from the change in the cathode potential occurred somewhat later than the equivalence point so that the difference between these two end-points was about 0.02 — 0.03 ml of 0.1 N HC104. This is explained by the occurrence of concentration polarization due to the flow of constant current, which causes an increase in the concentration of hydrogen ions at the anode and a decrease at the cathode. The curve obtained by the derivative polarographic titration represents the differences in the anode and cathode potentials during titration. This difference is greatest at the equivalence point. The comparison of the results obtained by the derivative polarographic titration with antimony and quinhydrone electrodes shows that the end-point is more sharply pronounced in the presence of quinhydrone electrodes (Fig. 1). The advantage of the antimony electrodes lies in the fact that the potential is established almost instantly. During titration of the halogen salts of organic bases in the presence of mercuric acetate the antimony electrodes amalgamate and at these amalgamated electrodes the potential is not established so fast. The results obtained by derivative polarographic titration of sodium benzoate with antimony electrodes are recorded in Table 1, while the titrated systems and the results obtained are listed in Table 2. TABLE 1 Taken Consumed Found No. HC104 Solvent g ml g I. 0.1000 6.91 0.0996 10 ml CH3 COOH + 10 mUCHjCO^O 2. 0.1000 6.94 0.1000 11 3. 0.1000 6.94 0.1000 »1 4. 0.1000 6.94 0.1000 ** 5. 0.1000 6.91 0.0996 ft 6. 0.1000 6,92 0.0997 M 7. 0.1000 6.94 0.1000 *» Mean value - 0.0998 i 0.0002* * ± 0.0002 is the average deviation inCHsOOHHg(CH3COO)2 CH,COOH10mlh 10mllOmlCHCOOH3% + CH,COOH20ml mlCH3COOH20 CH3COOH20ml 10ml(CH3CO)20 + Solvent »» »» »» »' »» II M »> »* ElectrodesAntimonyQuinhydroneElectrodes ofPresenceIntheInthe 0.05000.0001 ; titrations PolarographicDerivative Found g 0.14850.0000± 0.1464±0.0001 0.09970.0000± 0.00010.0813± 0.0838±0.0000 0.19870.0001± 0.28240.0001± 6080.00020.1± ofNo Titr. 4 6 4 2 2 2 2 3 4 0.1501±0.0C03 Found 0.0999±0X003 0.0999±0X002 g 0.0501±0.0001 8480.10.0000± 0.14630.0001± 0.09960.0001± 0.0813±0.0001 ±0.00000.0834 9870.00010.1± 0.28260.0005± 6.0003 0.1605± 0.1998±0.0005 0.14990.0003± 0.10.0002497± carriedpharmaceuticalwithproducts.*Thedeterminationsoutwere TABLK2 ofNo.

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