ELECTROCHEMICAL STUDIES OF 5-SUBSTITUTED 2-ALKYLIDENE-4 OXOTHIAZOLIDINES I. Cekić 1, V. Jovanović 2, R. Marković 3, D.M. Minić 1 1 Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12, Belgrade, Serbia Introduction Push-pull alkenes are substituted olefins containing one or two electron-donating substituents (EDG) at one end of the C=C bond, and one or two electron-withdrawing substituents (EWG) on the other end (structure A, Scheme). The central C=C bond becomes more polarized with increased π-electron delocalization (structure B) and con­se­quently, as the π-bond order decreases, the corresponding π-bond orders of the C-EDG and C-EWG bonds increase (structure C), rising the push-pull character of the compound. The combination of these effects has influence on physicochemical pro­per­ties and chemical reactivity of this class of compounds 1. Experimental Cyclic voltammetry (CV) was performed on a CHI760b Electrochemistry workstation (CHI Instrument CO., USA) using one- compartment electrolytic cell (volumetric capacity 10 ml) with a three-electrode configuration. A platinum disc (CH Instruments, Inc.) 2.0 mm diameter, was used as working electrode. The working electrode was mechanically refreshed with emery paper of decreasing grain size, polished with alumna (0.5 particle size) and cleaned in 18 M water in an ultrasonic bath. For each experiment the electrode prepared was first examined in basic electrolyte by CV before the substance was added in the solution. The counter electrode was a platinum flag wire. A silver wire in 0.01M AgNO 3 solution of TBAHF 6 in acetonitrile (anhydrous) served as a non- aqueous reference electrode which was separated from the rest solution by a fine glass frit. The experiments were performed in predried solution of 4mM 5-substituted 2- alkylidene-4-oxothiazolidine derivatives in 0.1 M TBAHF 6 in acetonitrile at room temperature with sweep rate of 50, 100, and 500 mV/s in the potential range from -2 to 1,6 V. References: 1.1. R. G. Giles, N. J. Lewis, J. K. Quick, M.J. Sasse, M. W. J. Urquhart, Tetrahedron, 56, (2000), , (2000), R. Marković, M. Baranac, Z. Džambaski, Heterocycles 63 (2004) J.-C. Zhuo, Magn. Reson. Chem. 35 (1997) J-M. Lehn, Angew. Chem. Int. Ed. Engl. 29 (1990) R. Marković, Z. Džambaski, M. Baranac, Tetrahedron, 57 (2001) R. Marković, M. Baranac, Z. Džambaski, M. Stojanović, P.J. Steel, Tetrahedron 59 (2003) Conclusions Stereodefined 5-substituted 4-oxothiazolidines depicted by general formula 1, exemplify typical push-pull compounds, which have attracted our attention due to potential biological activity, and as useful intermediates for the synthesis of different heterocyclic systems 2.These compounds also represent an excellent model for investigation of the effects of weak non-covalent interactions on the structure-reactivity relationship in a solution and in the solid state, as well 3,4. Characterization of these compounds has been previously done by 1 H NMR and 13 C NMR, IR, UV and MS spectroscopy and X-ray structural analysis 5,6. Fig. 1: Cyclic voltammogram of thiazolidinone derivative 1b in 0,1M TBAHP 6 in acetonitrile, different sweep rates Currently, the focus of our interest is research on electrochemical behaviour of the variously 5-substituted 2-alkylidene-4-oxothiazolidines 1 by cyclic voltammetry on Pt electrode in non-aqueous medium with an aim to determine: (i) the influence of the substituents at C(5)-position of the thiazolidine ring and (ii) electron withdrawing groups, on processes of the electrochemical reduction and oxidation. oxidation. Fig. 2: Cyclic voltammograms of derivatives 1a, 1b and 1c in 0,1M TBAHP 6 in acetonitrile, sweep rate 100 mV/s Ciclovoltammograms for all three compounds indicate the existence of irreversible anodic and cathodic peaks. The peak potentials in acetonitrile + 0,1M TBAHP 6 solutions are presented in Table 1. A detailed study on both electrochemical reduction and oxidation was performed with aim of establishing the influence of the supstituents in the heterocyclic ring. Based on the fact presented above may be concluded that, in non-aqueous solution 5-substituted-2-alkylidene-4-oxothiazolidines undergo oxidation and reduction processes at the potentials depending on the nature of substituents at C(5)-position of the thiazolidine ring. Correlation between the chemical structure of 5-substituted- 2-alkylidene-4-oxothiazolidines and electrochemical reactivity are also discussed. COMPOUND MeCN (vs Ag/Ag + ) Cathodic peaks Anodic peaks E p,c1 (V) E p,c2 (V) E p,c3 (V) E p,a1 (V) E p,a2 (V) 1a -1,28-1,65-0,320,641,31 1b -1,39-1,82-0,300,381,32 1c -1,23-1,77 _ 0,501,40 Table 1. The peak potentials of the compounds 1-c versus Ag/Ag+)