Kinetics of Ru (III)-catalysed Oxidation of Chalcones by Acid Bromate in H2SO4 -HOAc Medium

Abstract

Kinetics of Ru(III) chloride catalysed oxidation of chalcone and some substituted chalcones by acid bromate have been studied in acetic acid-sulphuric acid medium in the temperature range 303-318 K. The reaction is first order each in [chalcone] and [Ru(III)] and zero order each in [H ⁺] and [BrO<img src='/image/spc_char/3_bar.gif' border=0>)]. The rate increases with increase in the percentage of acetic acid and the plot of log <em>k</em>_o versus 1/D is linear with a positive slope indicating the positive ion-dipole nature of the reaction. The order of reactivities of various substituted chalcones with substituents in phenyl ring is: <em>p</em>-CH₃ &gt; <em>m-</em>CH₃ &gt; H &gt; <em>p</em>-Cl &gt; <em>m-</em>NO₂ &gt; <em>p-</em>NO₂. A radical mechanism involving the chalcone and Ru(III) in the slow step followed by oxidation of Ru(II) by BrO<img src='/image/spc_char/3_bar.gif' border=0> to Ru(III) in the fast step is proposed.