The rate of oxidation of isopropyl alcohol by potassium persulfate at 60°in aqueous solution of pH 8.0 and ionic strength 0.5 is first order with respect to the measured disappearance of persulfate. The rate constant is proportional to initial alcohol concentration at low concentrations but becomes independent of it at higher concentrations. The variation of the pseudo first-order constant with initial persulfate concentration, using 0.02 M isopropyl alcohol and initial concentrations of persulfate ranging from 0.00125 to 0.06 M, has now been investigated, and it is found, rather surprisingly, that a limiting initial rate is also attained at the higher initial persulfate concentrations, similar to that observed when initial alcohol concentration is varied. The rate equation -/át -kP = [ímax^4o.Po/(Z> + A<,){c + Po)]R (where b and c are empirical constants) relates the observed rate constant k to the initial alcohol and persulfate concentrations (Ao and P"). This equation is in excellent agreement with the data for 18 kinetic runs.The analogy between persulfate oxidation kinetics and enzyme kinetics is pointed out.
Abstract For alkyl groups it is shown that new inductive substituent constants, σI (R), can be calculated accurately from previously obtained polar substituent constants, σ*(R), from the simple relation σI(R) = σI (Me) [I-2σ* (R)]. In similar fashion, the two reaction constants are related by ρI/ρ* = σ* (H)/σI (Me) = 10.6. Many new σI values are presented for groups for which no previous estimate has been available. The attentuation of σI (R) with alkyl size for n-alkyl groups is shown to be a function of the number of C atoms, nc: σI(R) = -0.137 nc/(2nc + 1). The effect of branching of R is also discussed.
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