Oxidation of Phosphorous Acid by Peroxodisulfate Ions

As a third and final example of a chain reaction, we shall consider a net reaction that produces sulfate and hydrogen phosphate ions.7 The scheme is more intricate than the earlier ones. It starts with the homolytic dissociation of S2Ojj- as one of two parallel initiation steps, and utilizes SO -, HO, and HPO - as intermediates. The scheme suggested is shown here, and one can easily allow for the products that are identical save for protonation  

These reactions are followed by a rapid hydrolysis to the stable product,  

Adding these three affords one of the steady-state concentrations  

With the long-chain approximation (see Problem 8-2), an expression for the rate is obtained that agrees with the experimental findings, 

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