Kinetics of the iodate reduction by hydrogen peroxide and relation with the Briggs-Rauscher and Bray-Liebhafsky oscillating reactions

摘要

The iodate reduction by hydrogen peroxide in acidic solutions is part of the Bray-Liebhafsky and Briggs-Rauscher oscillating reactions. At low hydrogen peroxide concentrations, typical of the Bray-Liebhafsky reaction, its rate law is -d[IO3~-]/dt = (k'_R + [H+])[IO3~-][H2O2] with k'_R = 1.3 x 10~(-7)(20°), 7.8 x 10~(-7) (39°), 1.4 x 10~(-5) M~(-1) s~(-1) (60°) and k"_R = 1.5 x 10~(-5)(25°), 6.2 x 10~(-5) (39°), 6.3 x 10~(-4) M~(-2) s~(-1) (60°). It is explained by a non-radical mechanism. At high hydrogen peroxide concentrations, typical of the Briggs-Rauscher reaction, a new reaction pathway appears with a rate more than proportional to [H2O2]~2 and nearly independent of [IO3~-] > 0.01 M. This pathway is inhibited by scavengers of free radicals. We suggest that it has a radical mechanism starting with IOH + H2O2 <-> IOOH + H2O and IOOH + H2O2 → IO~· + H2O + HOO~·.