4-Heptanone cyclic diperoxide: Improved preparation method and solvent effect on its thermolysis in solution

Abstract

Cyclic organic peroxides have interesting pharmacological properties and are used at industrial level as polyfunctional initiators of polymerization, and so their preparation through novel methods has attracted the attention of numerous researchers. White crystals of 4-heptanone cyclic diperoxide (HDP) can be obtained in acidic media at −1°C by a reaction between 4-heptanone and hydrogen peroxide. Its thermal decomposition was studied in acetone, cyclohexane, acetonitrile, ethyl acetate, ethanol, 2-propanol, 2-butanol, and 1,4-dioxane at temperatures higher than 120°C, showing a behavior accordingly with a pseudo-first-order kinetic law up to at least 80% HDP conversion. It was demonstrated that an increase in solvent polarity is accompanied by an increase in reaction rates. The effect of solvent polarity on the thermal decomposition rate constant values can be associated with a reaction mechanism involving a more dipolar-activated complex than the diperoxide initial molecule. The activation parameters varied widely from 31.2 to 46.6 kcal mol−1 and −1.33 to 31.7 cal mol−1 K−1 when going from ethanol to cyclohexane as reaction solvents, respectively. An enthalpy–entropy compensation effect was observed in all solvents. Specific interactions between the oxygen atoms from the peroxidic bond and the hydrogen atom bonded to C2 and/or from the OH group can be taken into account to explain that the existence of the compensation effect does not mean that an isokinetic relationship consequently can be established. The kinetic results showed that an isokinetic relationship is observed only for a group of solvents.