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Abstract The rates of oxidation of phenylthioacetic acid （PTAA） and several substituted phenylthioacetic acids by potassium peroxodiphosphate （PP） in 50% （v/v） aqueous acetic acid have been studied in detail. The rate of oxidation is expressed as An analysis of the dependence of the rate on [H+] reveals that H3P2O 8 ? is the active oxidizing species in the oxidation. The effect of ring substituents on the rate gives a ρ+ value of ‐0.45 ± 0.03 （ r = 0.998, s = 0.02 at 40°C）, pointing to the development of an electron‐deficient center in the transition state. The results are discussed in terms of a mechanism involving the rate‐determining formation of an intermediate between PP and phenylthioacetic acids, followed by the decomposition of the intermediate. These kinetic results are compared with those obtained in the oxidation of phenylthioacetic acids by peroxodisulfate.
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