Kinetics of the redox reactions between ceric sulfate and lactic and atrolactic acids in the medium HClO4-Na2SO4-NaClO4

The kinetics of the oxidation of lactic and atrolactic acids by ceric sulfate have been studied in the medium HClO4‐Na2SO4‐NaClO4 at 25.0°C and ionic strength 2.0 mol dm−3 over a wide range of organic substrate (HL), hydrogen and bisulfate ion concentrations. The redox reactions proceed significantly through three simultaneous paths involving intermediate complexes between the reactive cerium(IV) species and the organic substrate according to the following expression \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \frac{{(b[{\rm HSO}_4^ -] + c[{\rm HSO}_4^ -]^2 + [{\rm H}^ +]){\rm [HL]}}}{{\{ f_1 [{\rm HSO}_4^ -]^3 + d_1 [{\rm HSO}_4^ -] + e_1 [{\rm HSO}_4^ -]^2){\rm }[{\rm H}^ +]\} + A'[{\rm HL}]}}$$\end{document} where kobs indicates the observed pseudo‐first‐order rate constant, b and c are rate constants relative to that for the path associated with the term [H+] in the numerator, and A' is a quantity depending on the [H+] and [HSO 4−] concentrations. Moreover, three equilibria involving cerium(IV) and HSO 4− (or SO 42−) ions are important from a kinetic point of view, the cumulative equilibrium constants being in the ratios β1: β2: β3 = d1: e1: f1. The present data are compared with those obtained previously for the cerium(IV) oxidation of glycolic acid and the substituent effects discussed.