The N-Hydroxyphthalimide catalyzed oxidation of cyclohexene to cyclohexenyl hydroperoxide: Reasons for deactivation and stability of the catalyst

Selective oxidation of cyclohexene to cyclohexenyl hydroperoxide catalyzed by N-hydroxyphthalimide (NHPI) was studied. Kinetic observations and 13C and 1H NMR spectroscopy showed that accumulation of cyclohexenyl hydroperoxide was accompanied by deactivation of the catalyst. A mechanism of the deactivation through phthalimido N-oxyl radical (PINO) addition to vinyl position of olefin was suggested. Responsible for the deactivation, PINO-C6H10-OOH hydroperoxide adducts were detected in the reaction conditions, and their molecular structure was elucidated by DFT technique. The mechanism explained an unexpected experimental effect, that is, lowering the oxygen partial pressure improved the stability of NHPI without decrease in production of cyclohexenyl hydroperoxide.