Chlorobenzene, perester decomposition

Several investigations have been concerned with the effect of solvent upon the rate of perester decomposition. These data also shed some light on the importance of the ionic structure (II) in the transition state. Some data on the effect of solvent may be obtained from previous tables. For the decomposition of peresters where R is a primary alkyl group in RCO3C4H9-/ and one-bond homolysis is the mechanism of choice, changes in solvent polarity have little effect on the rate of decomposition. The rate coefficients for the decomposition of r-butyl percaprate at 110 °C in chlorobenzene, nitrobenzene and diphenyl ether are 8.30 x 10 , 6.58 x 10" and 6.39 X 10" sec"S respectively" . The rates are also independent of initial concentration of the peroxide this may indicate that induced decomposition is unimportant cf. sub-section 13.4.1). 

The A5 term also appears to be sensitive to solvation effects in the two-bond concerted homolysis reaction. This is particularly evident for R is (CH3)jC in Table 91. It should be noted that some, but not all, of the entropies of activation in chlorobenzene solvent are more positive than predicted from the AH vs. AS plot for 38 peresters. For example, from the parameters given above, AS for R is (CH3)3C is calculated to be 6.32+0.19 eu in chlorobenzene where AH = 30.0 kcal.mole". This is in contrast to the reported value of 11.1 eu. Induced decomposition would be the most likely explanation for this disparity in AS values. Indeed, kinetic data for the decomposition of bicyclic peresters in chlorobenzene and cumene suggests that induced decomposition is more important in chlorobenzene (see section 13.4.9). 

FUNCTIONAL GROUP PROXIMITY EFFECTS IN THE DECOMPOSITION OF /-BUTYL PERESTERS IN CHLOROBENZENE... 

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