Interactive free energy relationships in the Os(VIII) catalysed oxidation of chalcones by acid bromate: A kinetic study

Abstract

The kinetics and mechanism of Os(Vlll) catalysed oxidation of chalcones by acid bromate with special reference to interactive free energy relationships have been studied. The reaction is zero order in [BrO<img src='/image/spc_char/3_bar.gif' border=0>], fractional order in [chalcone] and first order in [Os(VIll)]. The reaction is enhanced by electron releasing substituents both in benzaldehyde and acetophenone moieties. The magnitude of <i>ρ </i> value obtained for various substituents in benzaldehyde moiety decreased with the introduction of electron releasing groups in acetophenone moiety and vice versa. A linear plot is obtained between <i>ρ</i>_X(Y) (obtained from the Hammett's plot for various substituents in benzaldehyde moiety) and σ_y (substituent constant for substituents in acetophenone moiety) with a slope (q_Y ) of 1.02 ± 0.01. Similarly a linear plot is obtained between <i>ρ</i>_Y(X) (obtained from the Hammett's plot for various substituents in acetophenone moiety) and <i>σ_x </i> (substituent constant for substituents in benzaldehyde moiety) with a slope (q_x) of 0.92 ± 0.01. These relationships have been analysed quantitatively in terms of interactive free energy relationships for multiple substituent effects.