Decomposition of Six-membered Ring Hydroperoxides

Abstract

Four secondary hydroperoxides with six-membered rings, i, e., cyclohexyl hydroperoxide, 2-chlorocyclohexyl hydroperoxide, 2-tetrahydropyranyl hydroperoxide and 1, 4-dioxanyl hydroperoxide, were prepared and subjected to thermal decomposition in benzene. The first order rate constants, the activation energies and entropies were determined. Then the relationship between their structures and these kinetic date were examined.
The examination of the IR and NMR spectra of these hydroperoxides reveals that cyclohexyl and 2-chlorocyclohexyl hydroperoxides have equatorial hydroperoxy groups whereas 2-tetrahydropyranyl and 1, 4-dioxanyl hydroperoxides have axial ones. Intermolecular hydrogen bonding is greatly reduced in such dilute solutions as those used in our experiments and no intramolecular hydrogen bonding is present in the solution of 1, 4-dioxanyl hydroperoxide. The dissociation energies of the O-O bonds of these hydroperoxides were found to be nearly the same and 30 kcal/mol and do not depend upon the number of oxygen atoms, their positions in the ring and the conformation of these hydroperoxides molecules.
1, 4-Dioxanyl hydroperoxide decomposes extremely faster than other hydroperoxides and the activation entropy is positive. It could be explained in terms of the repulsion between oxygen atoms of the axial hydroperoxy group and those of the 1 and 4-position in the 1, 4-dioxane ring.