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The chemicali mechanism of Field, Karas, and Noyes for the osclllatory Belousov reaction has been generalized by a model composed of five steps involving three independent chemical intermediates, The behavior of the resulting differential equations has been examined numerically, and it has been shown that the system traces a stable closed trajectory in three dimensional phase space, The same trajectory is attained from other phase points and even from the point corresponding to steady state solution of the differential equations. The model appears to exhibit limit cycle behavior. By stimy coupling the concentrations of two of the intermediates, the limit cycle model can be simplified to a system described by two independent variables; this coupled system is amenable to analysis by theoretical techniques already developed for such systems.

The reactions constituting the mechanism of the oscillatory Belousov-Zhabotinskii (BZ) reaction may be divided into an inorganic and an organic subset. The former is well established and generally accepted, but the latter remains under development.There has been considerable work on component reactions of the organic subset over the past few years, but little effort has been made to incorporate the results of this work into an improved BZ mechanism. We do so and present a BZ mechanism containing 80 elementary reactions and 26 variable species concentrations and which implements recent experimental results and suggestions concerning the complicated organic chemistry involved. The possible role of organic radicals as a second control intermediate is explored. The rate constants of the inorganic subset also are adjusted for acidity effects. The performance of the model in simulating either quantitatively or semiquantitatively a number of recent BZ experiments is substantially better than that of previous models. Several areas in need of further work are identified.

A revised set of rate constants at 20 °C and in 1 M H2S04 is developed for the Field-Kórós-Noyes mechanism of the 4Ce(III) + BrOf + 5H+ -4Ce(IV) + HOBr + 2H20 component of the oscillatory Belousov-Zhabotinskii reaction. The mechanism involves 10 species and 8 reversible reactions. Our results are based on the recognition that the reaction HBr02 + BrOf + H+ ^2Br02" + H20 is strongly reversible and is in fact close to equilibrium under normal Belousov-Zhabotinskii conditions where [Ce(III)] « [BrOf]. This is not true if Fe(phen)32+ is substituted for Ce(III). We find the equilibrium constant to be about 1 X 10-6 NT1. This value leads to AGf°(HBr02) s -0.4 ± 1 kJ/mol and pKa(HBr02) =t 4.9. The species HBr02 is thus considerably more stable than has been assumed previously. This value of AGf°(HBr02) is combined with other thermodynamic data, several recent determinations of the rate constants of individual component reactions, and data on the overall process to yield a complete set of rate constants that is thermodynamically consistent and in essential agreement with all known direct kinetic measurements. The resulting values are very close to the "Lo" values derived by Tyson except that k for HBr02 + BrOf + H+ -2Br02* + H20 is somewhat higher than proposed by him. They are able to simulate very accurately simultaneous data on [Ce(IV)] and [BrOf] in the overall reaction of Ce(III) with brómate even when the

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