Electrochemical reduction of 2-acetyl benzofuran and its derivatives at glassy carbon electrode

G Mamatha, B Sherigara, K Mahadevan
2007 Indian Journal of Chemical Technology   unpublished
Electrochemical reduction of 2-acetylbenzo[b]furan and its derivatives namely 2-acetylbromobenzo[-b]furan, 2-acetylbromo-5-bromobenzo[b]furan and 2-acetyl naphtha[2,1-b] furan has been carried out in four different aqueous solvents namely DMSO, DMF, acetonitrile, ethanol using Britton Robinson buffer as supporting electrolyte at glassy carbon electrode employing cyclic voltametric techinque. Single irreversible wave was observed due to the reduction of >C=O moiety to secondary alcohol
more » ... s of benzofuran. Formation of pinacol due to dimerization of the intermediate radical was ruled out on steric consideration. The other data viz. the effect of sweep rate, concentration of the electroactive species, effect of temperature, effect of surfactant, effect of dielectric constant on cathodic peak potential (E pc), and cathodic peak current (i pc) has been found out. Diffusion coefficent (D 0) and heterogeneous rate constant (k 0) have been evaluated. The electrode process was shown to be diffusion controlled and irreversible. The electrolytic products are characterised/identified by controlled potential electrolysis. The results of the electroreduction are compared with that of the chemical reduction method. Benzo[b]furan derivatives are an important class of organic compounds, which are known to be present in many natural products 1 and possess physiological activity. They find applications in agrochemicals 2,3 , pharmaceuticals 4-10 and cosmetics 11,12. Benzo[b]furans are building blocks of optical brightners 13. Synthetic 2-acetylbenzo[b]furan and its derivatives are found to possess wide range of biological activities such as antiviral, antimicrobial, anti-inflammatory and analgesic 14-19. Reduction of 2-acetylbenzo[b]furan by sodiumborohydride yields secondary alcohol derivative of benzofuran 20. In an effort to understand the mechanism of electro reduction/oxidation of various molecules 21-26 , results of the investigations on the electrochemical reduction of 2-acetyl benzo[b]furan and its derivatives in four different aqueous solvents namely ethyl alcohol, dimethyl formamide (DMF), acetonitrile and dimethyl sulphoxide (DMSO), at different pH at glassy carbon electrode are presented here. Experimental Procedure All the reagents were of analytical grade. 2-Acetylbenzo[b]furan and its derivatives (i) 2-acetylbromobenzo[b]furan (ii) 2-acetylbromo-5-bromobenzo[b]furan 27 and (iii) 2-acetyl naphtho furan 28 were prepared as reported in literature. 2-acetylbromobenzo[b]furan was prepared by the reaction of salicylaldehyde with chloroacetone in potassium carbonate. 2-Acetylbromo-5-bromobenzo[b]furan was prepared by the reaction of 2-acetyl benzofuran with bromine in acetic acid, chloroacetone with 6-bromosalicylaldehyde. 2-acetyl naphtho furan was prepared by the reaction of salicylaldehyde with 2-hydroxy-1-naphthaldehyde in potassium carbonate, acetone and chloroacetone. The products were recrystallised from ethanol. The purity of compounds were tested by thin layer chromatography and its melting point. Method Cyclicvoltammetric measurements of the above said compounds in different partially aqueous media using DMF, DMSO, acetonitrile, ethanol were carried out using Britton Robbinson buffer as supporting electrolyte in a cell at 298 K. All samples were purged well with nitrogen to remove any dissolved oxygen before voltammetric measurements were recorded.