Catalytic performance and mechanisms of GOase model compound on selective oxidation of ethylbenzene to acetophenone

Selective oxidation of C—H bonds under mild conditions plays an important role in the production of fine chemicals. Inspired by the active center structure and catalytic cycle of galactose oxidase, model compound CuL, with L referring to the ligand of N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2'diaminonaphthyl, was synthesized, and evaluated for its catalytic performance as well as mechanism on selective oxidation of ethylbenzene to acetophenone using N-hydroxyphthalimide (NHPI) as cocatalyst. The results showed that under mild conditions (initial O2 pressure 1.0 MPa, 75 ℃, reaction time 8 h), the conversion rate of ethylbenzene was up to 99%, while the selectivity of acetophenone was also up to 99%. The reaction mechanism could be attributed to the active intermediates formed by CuL and NHPI, which efficiently promoted NHPI generating phthalimide N-oxyl (PINO) radicals through electron transfer and thus achieved the C—H bond activation of ethylbenzene. Data from kinetic isotope effect experiments suggested that the activation of NHPI might be a rate-determining step (the ratio of reaction rates between NHPI and deuterated NHPI was about 3.4). The results of electron paramagnetic resonance and high-resolution mass spectrometry revealed that there were alkyl radicals, peroxy radicals and hydroxyl radicals generated during the reaction. © 2024 Fine Chemicals. All rights reserved.