KINETIC STUDIES ON AUTOXIDATION OF PHENYLHYDRAZONES

Detailed kinetic studies were carried out on the thermally initiated autoxidation of cyclohexanone phenylhydrazone (CHPH) and cyclopentanone phenylhydrazone (CPPH) to their corresponding phenylazoalkane hydroperoxides. The rate of oxidation was measured over the range of 0-35° in four different solvents, i.e., benzene, re-heptane, acetone, and methanol. In all solvents, CHPH was oxidized more rapidly than CPPH, reflecting the sterochemistry of the cyclohexane and cyclopentane ring systems at the carbon-nitrogen linkage during the allylic rearrangement of the intermediate free radical which takes place in the autoxidation process. The rate of oxidation of both CHPH and CPPH is more rapid in nonpolar solvents than in polar solvents. A compensation effect was observed with CPPH; it has oxidized more rapidly in benzene than in acetone, but the observed activation energy was less (11.5 vs. 7.3 kcal/mol). These results suggest that solvent-phenylhydrazone interaction is greater than solvent-radical interaction. © 1969, American Chemical Society. All rights reserved.