ELECTROCHEMICAL STUDIES OF 5-SUBSTITUTED ELECTROCHEMICAL STUDIES OF 5-SUBSTITUTED 2-ALKYLIDENE-4 OXOTHIAZOLIDINES2-ALKYLIDENE-4 OXOTHIAZOLIDINES

I. CekićI. Cekić11, V. Jovanović, V. Jovanović22, R. Marković, R. Marković33, D.M. Minić, D.M. Minić11

11Faculty of Physical Chemistry, Faculty of Physical Chemistry, University of Belgrade, University of Belgrade, Studentski trg Studentski trg 12, 1112, 11 00000 0 Belgrade, SerbiaBelgrade, Serbia

IntroductionIntroduction

Push-pull alkenes are substituted olefins containing one or two electron-donating substituents 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) (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 on the other end (structure A, Scheme). The central C=C bond becomes more polarized with increased π-electron delocalization (structure B) and con se quently, as the π-bond order increased π-electron delocalization (structure B) and con se quently, as the π-bond order decreases, the corresponding π-bond orders of the C-EDG and C-EWG bonds increase 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 (structure C), rising the push-pull character of the compound. The combination of these effects has influence on physicochemical pro per ties and chemical reactivity of this class of has influence on physicochemical pro per ties and chemical reactivity of this class of compoundscompounds11..

ExperimentalExperimental

Cyclic voltammetry (CV) was performed on Cyclic voltammetry (CV) was performed on a CHI760b Electrochemistry workstation a CHI760b Electrochemistry workstation (CHI Instrument CO., USA) using one-(CHI Instrument CO., USA) using one-compartment electrolytic cell (volumetric compartment electrolytic cell (volumetric capacity 10 ml) with a three-electrode capacity 10 ml) with a three-electrode configuration. A platinum disc (CH configuration. A platinum disc (CH Instruments, Inc.) 2.0 mm diameter, Instruments, Inc.) 2.0 mm diameter, was was used used as working electrodeas working electrode.. The working The working electrode was mechanically refreshed with electrode was mechanically refreshed with emery paper of decreasing grain size, emery paper of decreasing grain size, polished with alumna (0.5 polished with alumna (0.5 particle size) particle size) and cleaned in 18 Mand cleaned in 18 M water in an ultrasonic water in an ultrasonic bath. For each experiment the electrode bath. For each experiment the electrode prepared was first examined in basic prepared was first examined in basic electrolyte by CV before the substance was electrolyte by CV before the substance was added in the solution.added in the solution. The counter electrode The counter electrode was a platinumwas a platinum flag flag wire wire.. A silver wire in A silver wire in 0.01M AgNO0.01M AgNO33 solution of TBAHF solution of TBAHF66 in in

acetonitrile (anhydrous) served as a non-acetonitrile (anhydrous) served as a non-aqueous reference electrode which was aqueous reference electrode which was separated from the rest solution by a fine separated from the rest solution by a fine glass frit. glass frit. The experimentsThe experiments were performed were performed in predried solution of 4mM 5-substituted 2-in predried solution of 4mM 5-substituted 2-alkylidene-4-oxothiazolidine derivatives in alkylidene-4-oxothiazolidine derivatives in 0.1 M TBAHF0.1 M TBAHF66 in acetonitrile in acetonitrile at room at room

temperaturetemperature with sweep rate of 50, 100, and with sweep rate of 50, 100, and 500 mV/s 500 mV/s in the potential range from -2 to in the potential range from -2 to 1,61,6 V V..

References:References:

1.1. 1. R. G. Giles, N. J. Lewis, J. K. Quick, M.J. Sasse, M. W. J. Urquhart, Tetrahedron, 1. R. G. Giles, N. J. Lewis, J. K. Quick, M.J. Sasse, M. W. J. Urquhart, Tetrahedron, 56, (2000), 4531-453756, (2000), 4531-45372. 2. R. MarkoviR. Markovićć, M. Baranac, Z. Džambaski, Heterocycles 63 (2004) 851, M. Baranac, Z. Džambaski, Heterocycles 63 (2004) 85133. J.-C. Zhuo, . J.-C. Zhuo, Magn. Reson. ChemMagn. Reson. Chem. . 3535 (1997) 311 (1997) 31144. J-M. Lehn, . J-M. Lehn, Angew. Chem. Int. Ed. EnglAngew. Chem. Int. Ed. Engl. . 2929 (1990)1304 (1990)130455. R. Markovi. R. Marković, ć, Z. Džambaski, M. Baranac, Tetrahedron, 57 (2001) 5833Z. Džambaski, M. Baranac, Tetrahedron, 57 (2001) 583366. R. Markovi. R. Markovićć, M. Baranac, Z. Džambaski, M. Stojanovi, M. Baranac, Z. Džambaski, M. Stojanović, P.J. Steel, Tetrahedron 59 ć, P.J. Steel, Tetrahedron 59

(2003) 7803.(2003) 7803.

Conclusions

Stereodefined 5-substituted 4-oxothiazolidines depicted by general formula Stereodefined 5-substituted 4-oxothiazolidines depicted by general formula 11, exemplify typical , exemplify typical push-pull compounds, which have attracted our attention due to potential biological activity,push-pull compounds, which have attracted our attention due to potential biological activity, and and as useful intermediates for the synthesis of different heterocyclic systemsas useful intermediates for the synthesis of different heterocyclic systems22 .These compounds .These compounds also represent an excellent model for investigation of the effects of weak nonalso represent an excellent model for investigation of the effects of weak non--covalent covalent interactions on the structure-reactivity relationship in a solution and in the solid state, as wellinteractions on the structure-reactivity relationship in a solution and in the solid state, as well 33,4.,4.

S

NH

O

R

EWG

H1R = H, Me or CH2CO2EtEWG = COPh, CO2Et, CONHPh, CONHCH2CH2Ph or CN

Characterization of these compounds has been previously done by Characterization of these compounds has been previously done by 11H NMR and H NMR and 1313C NMR, C NMR, IR, UV and MS spectroscopy and X-ray structural analysisIR, UV and MS spectroscopy and X-ray structural analysis5,65,6..

2,0 1,5 1,0 0,5 0,0 -0,5 -1,0 -1,5 -2,0 -2,5

-0,00014

-0,00012

-0,00010

-0,00008

-0,00006

-0,00004

-0,00002

0,00000

0,00002

0,00004

0,00006

0,00008

0,00010

0,00012

V

IV

III

II

HN

S

COOEt

OH

C NHPh

O

i p (

A)

E (V vs Ag/Ag+)

v = 50 mV/s v = 100 mV/s v = 500 mV/s

I

1b

Fig. 1:Fig. 1: Cyclic voltammogram Cyclic voltammogram of thiazolidinone derivative of thiazolidinone derivative 1b 1b in 0,1M TBAHPin 0,1M TBAHP66 in acetonitrile, different sweep rates in acetonitrile, different sweep rates

Currently, the focus of our interest is research on electrochemical behaviour of the Currently, the focus of our interest is research on electrochemical behaviour of the variously 5-substituted 2-alkylidene-4-oxothiazolidines variously 5-substituted 2-alkylidene-4-oxothiazolidines 11 by cyclic voltammetry on Pt by cyclic voltammetry on Pt electrode in non-aqueous medium with an aim to determine: electrode in non-aqueous medium with an aim to determine:

(i)(i) the influence of the substituents at C(5)-position of the thiazolidine ring and the influence of the substituents at C(5)-position of the thiazolidine ring and (ii)(ii) electron withdrawing groups, on processes of the electrochemical reduction and electron withdrawing groups, on processes of the electrochemical reduction and oxidation.oxidation.

Fig. Fig. 22:: Cyclic voltammogram Cyclic voltammograms of derivatives s of derivatives 1a1a, , 1b1b and and 1c1c in 0,1M TBAHP in 0,1M TBAHP66 in acetonitrile, sweep rate 100 mV/s in acetonitrile, sweep rate 100 mV/s

2,0 1,5 1,0 0,5 0,0 -0,5 -1,0 -1,5 -2,0 -2,5

-0,00008

-0,00006

-0,00004

-0,00002

0,00000

0,00002

0,00004

0,00006

IV

III

II

I

i p(A

)

E (vs Ag/Ag+)

1a 1b 1c

V

N

SH3C

OH

H

C NHPh

O

HN

S

COOEt

OH

C NHPh

O

N

S

O

COOEt

H

C

H

NHPh

O1a 1b 1c

Ciclovoltammograms for all three compounds indicate the existence of irreversible anodic Ciclovoltammograms for all three compounds indicate the existence of irreversible anodic and cathodic peaks. The peak potentials in acetonitrile and cathodic peaks. The peak potentials in acetonitrile + 0,1M TBAHP+ 0,1M TBAHP66 solutions are solutions are

presented in Table 1.presented in Table 1.

A detailed study on both electrochemical reduction and oxidation was performed A detailed study on both electrochemical reduction and oxidation was performed with aim of establishing the influence of the supstituents in the heterocyclic ring. 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 Based on the fact presented above may be concluded that, in non-aqueous solution 55--substitutedsubstituted-2-alkylidene-4-oxothiazolidines -2-alkylidene-4-oxothiazolidines undergo oxidationundergo oxidation and reduction and reduction processesprocesses at the potentials depending on at the potentials depending on the nature of the nature of substituents at C(5)-position substituents at C(5)-position of the thiazolidine ringof the thiazolidine ring.. Correlation between the chemical structure of Correlation between the chemical structure of 55--substitutedsubstituted--2-alkylidene-4-oxothiazolidines and electrochemical reactivity are also discussed.2-alkylidene-4-oxothiazolidines and electrochemical reactivity are also discussed.

COMPOUNDCOMPOUND

MeCNMeCN((vsvs A Ag/Agg/Ag++))

Cathodic peaksCathodic peaks Anodic peaksAnodic peaks

Ep,c1

(V)

Ep,c2

(V)

Ep,c3

(V)

Ep,a1

(V)

Ep,a2

(V)

1a -1,28 -1,65 -0,32 0,64 1,31

1b -1,39 -1,82 -0,30 0,38 1,32

1c -1,23 -1,77 _ 0,50 1,40

Table 1Table 1. The peak potentials of the compounds . The peak potentials of the compounds 1-c1-c versusversus A Ag/Ag+g/Ag+))