Experimental and computational investigations of C–H activation of cyclohexane by ozone in liquid CO2

摘要: Facile cyclohexane oxidation by ozone in liquid CO2 was demonstrated a Parr reactor equipped with situ infrared probe. The dominant presence of the vapor phase allows operation below lower flammability limit. At 280 K, 6.9 MPa and molar feed O3/cyclohexane ratio ≃0.5, conversion ∼12% during 1 h batch run cyclohexanone (K) + cyclohexanol (A) yield K/A being ∼11% ∼100, respectively. Small but measurable amounts hydrogen peroxide were also formed. absence any detectable water product close match rule out significant combustion. observed products are consistent reaction pathways predicted density functional theory (DFT) computations involve formation hydrotrioxide (HO3C6H11) intermediate. DFT-computed energetics initial hydrogen-atom transfer between O3 to give validated comparison multi-reference complete active space self-consistent field (CASSCF) computations, which included n-electron valence state perturbation (NEVPT2) for dynamic correlation. Even though DFT cannot properly treat multireference character O3, agreement these methods reasonable. Preliminary studies isooctane ozonation demonstrate that is capable activating all carbons (with preference primary carbon) producing variety oxygenated (alcohols, ketones acid) negligible combustion products. These results clearly ability selectively oxidizing C–H bonds alkanes.