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| - A Curve-Crossing Model for Oxidative Decarboxylation. Kinetics of Anilino CarboxylateFragmentations
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| - The kinetics of oxidative decarboxylation of a series of anilino carboxylates have been measured. Thesecompounds find use in the recently described two-electron sensitization process for silver halide photography,and control of their fragmentation kinetics is essential to be useful in this application. The measured rateconstants vary over 5 orders of magnitude. The decarboxylation rate constants decrease substantially withincreasing solvent polarity, an effect that results in misleading Arrhenius analysis of temperature effectmeasurements. The rate constants also depend on the product radical stability and the oxidation potential ofthe aniline precursor. A valence bond curve-crossing model is proposed that provides a combined picture ofthis and the related decarboxylation of acyloxy radicals. The model is able to explain the substitution andsolvent polarity effects. Consistent with this model, manipulation of solvation via changes in substituents(hydrophilic vs hydrophobic) around the reaction site is shown to strongly influence the decarboxylation rateconstants. In this way, the decarboxylation rate constants can be altered by nearly 3 orders of magnitude atconstant solvent polarity and precursor oxidation potential.
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