Dan Rozbroj supervisor: Dr. Jiří Ludvík

1. The Use of Electrochemical Limiting Currents in Determination of Viscosity in Mixtures of Water with Some Organic Co-solvents Dan Rozbroj supervisor: Dr. Jiří Ludvík

2. Electroreduction of triazines • deviations between limiting currents of various triazines • hypothesis:nucleophilic attack on double bond of triazines yielding covalent hydration and therefore blocked electroreduction of double bond • how to prove it? - to measure limiting currents of triazines in mixtures of water with nucleophiles of different strength • but: what about the effect of viscosity?

3. Relation between id and h • from Ilkovič equation: id is a linear function of the square root of the diffusion coefficient • from Stokes-Einstein equation: diffusion coefficient is indirectly proportional to viscosity of solution

4. Relation between id and h • to compare limiting currents obtained in mixtures of water with different co-solvents is necessary to make correction to different relative viscosity of solution however: • inconsistent literature data of viscosities for mixtures available • missing data for other mixtures

5. How to obtain viscosities? by measuring of dependence of limiting current on concentration of co-solvent in selected reference redox systems • with simple redox behaviour • without any nucleophilic adition • pH stable at least within 1 pH unit • for comparison metal ion as well as organic compound are useful

6. Conditions • Mixtures of Water with • ethanol • 2-propanol • acetonitrile • DMF • Ref. system • Tl+ • Cd2+ • 2-hydroxy-1,4- naphthoquinone pH 4,7 (0,1M acetate buffer) concentration of co-solvent 0 - 50% concentration of electrochem. active species 2·10-4 M

7. Realization • repeated measurements of id of choosen electrochem. active species in pure buffer (i0) and in 10, 20, 30, 40 and 50% concentration of co-solvent in water (i) • measured ratio i0/iis directly equal to square root of relative viscosity for each concentra-tion of co-solvent • to prove obtained data was used three different electrochemical active species (systems)

8. Advantages • measured ratio i0/i is independent of the concentration of the electroactive species, of the number of transferred electrons, and of the rate of the electrode process (its reversibility) • measurements of the relative viscosity proceed under the same conditions as the original electrochemical study to be corrected • measurements are simple and reliable • possibility of extension to other solvent mixtures

9. Results: relwater-2-propanol • References • 4 Timmermans, Jean, The Physico-Chemical Constants of Binary Systems in Concentrated Solutions, Vol. 4.: Systems with Inorganic + Organic or Inorganic Compounds (Excepting Metallic Derivatives); Interscience Publishers Inc., New York, USA 1960. • 6 Irany, G. P. J. Am. Chem. Soc. 1944, 65, 1396. • 7Handbook of Chemistry and Physics, 67th Ed. , Weast, R.C., Ed., CRC Press, Boca Raton, FL, USA, 1986-7, p. D-249.

10. Results: relwater-ethanol • References • 1 Noack, K. Wiedemann´s Ann. 1886,27, 289; 1886, 28, 666. • 2 Jones, H. C.; Getman, F. H. J. Am. Chem. Soc, 1904, 31, 303; 1904, 32, 308, 398.; Jones, H.C.; Getman, F.H.; Carn. Inst. Publ. No. 210,1915, 202. • 3International Critical Tables • 4 Timmermans, Jean, The Physico-Chemical Constants of Binary Systems in Concentrated Solutions, Vol. 4.: Systems with Inorganic + Organic or Inorganic Compounds (Excepting Metallic Derivatives); Interscience Publishers Inc., New York, USA 1960. • 5Handbook of Chemistry and Physics, 52nd Ed., Weast, R.C. Ed., CRC Press, Cleveland, Ohio, USA, 1971-2, p. D-188.

11. Results: relwater-DMF

12. Results: relwater-acetonitrile • References • 4 Timmermans, Jean, The Physico-Chemical Constants of Binary Systems in Concentrated Solutions, Vol. 4.: Systems with Inorganic + Organic or Inorganic Compounds (Excepting Metallic Derivatives); Interscience Publishers Inc., New York, USA 1960.

13. Results: rel1/2 - direct correction into the equation i = i0 / rel1/2

14. Conclusion • an independent method for the determination of the relative viscosity coefficients rel1/2 was developed • sets of data for mixtures of water with ethanol, 2-propanol, acetonitrile and DMF were obtained • electrochemical measurements open also the possibility of an extension of their use to solvent mixtures, for which no previously reported data are available, as demonstrated for the mixtures of DMF with water