Kinetics and Mechanism of the Chlorate-Bromide Reaction

Area of Science:

• Chemical kinetics
• Inorganic reaction mechanisms

Background:

• The chlorate-bromide reaction is complex and has been studied to understand its kinetics.
• Previous studies on related reactions, like chlorate-chloride, provide context for mechanistic investigations.

Purpose of the Study:

• To elucidate the rate law and propose a reaction mechanism for the chlorate-bromide reaction.
• To investigate the kinetic behavior at varying bromide concentrations and compare it to related systems.

Main Methods:

• Spectrophotometric monitoring of the reaction at the Br3(-)/Br2 isosbestic point (446 nm).
• Kinetic analysis to determine the reaction order and rate constant under specific conditions (25 °C, I = 2.4 mol L(-1)).

Main Results:

• A fifth-order rate law was determined: (1)/3 d[Br2]/dt = k[ClO3(-)][Br(-)][H(+)](3) with k = 5.10 × 10(-6) s(-1) L(4) mol(-4).
• Saturation kinetics were observed at high bromide concentrations, with the bromide order approaching zero.
• The observed behavior is analogous to the chlorate-chloride reaction.

Conclusions:

• The reaction mechanism likely involves the formation of a bromo-peroxychloro intermediate, BrOClO2(2-).
• The proposed mechanism accounts for the observed fifth-order kinetics and bromide saturation effects.
• This study contributes to understanding the reactivity of oxyanions with halide ions.