Kinetic relations and rate coefficients

Kinetic schemes for 02 oxidations can be written in the general form 

Young et al. [195] described a general competitive technique to evaluate relative rate coefficients in which the loss of standard compound, S2, is followed at different initial concentrations of S2, the rate expression being 

If ox[S2] is made small compared with other terms in the denominator, by keeping [S2] below 10 6 M, then the equation simplifies to 

Simple competitive techniques have also been used for estimating relative reactivity toward 02. Bartlett et al. [190] evaluated the relative rate coefficients for a series of vinyl ethers in acetone. Gollnick et al. [187] measured the reactivities for a series of olefins and Matsuuraet al. [197] measured the relative reactivities for cyclic olefins in methanol. The relative reactivities are expressed as the ratio of two first-order processes 

Kinetic parameters are not available for these reactions but in many cases their activation energies can hardly exceed 2—3 kcal mole-1 since the oxidations proceed nearly as rapidly at—170°C as at 25°C [177,181,182]. Indeed, the lack of significant temperature coefficients for these reactions may be the most reliable diagnostic procedure for distinguishing between oxidation by R02- and 02 the former process generally becomes immeasurably slow below 0°C, whereas the rate of the latter process may be scarcely affected by a change of 50—100°. This distinction may not apply, of course, to type I photooxidation processes where the triplet diradical 

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