CATALYTIC OXYGENATION OF CYCLOHEXANE BY PHOTOEXCITED (NBU(4)N)(4)W10O32 - THE ROLE OF RADICALS

Photochemical excitation of (nBu(4)N)(4)W10O32 in the presence of oxyg en (760 torr) leads to the formation of C6H11. and OH. radicals which can be revealed by ESR spin-trapping investigations. Cyclohexane is tr ansformed in cyclohexanone and cyclohexanol with an overall photooxida tion quantum yield of 0.35 at 325 nm photoexcitation wavelength. A str ong influence of oxygen pressure on the concentration ratio of these p roducts is observed; in that, at low oxygen pressure (15 torr), the yi eld of cyclohexanone is negligible and the photocatalytic oxidation of cyclohexane mainly leads to the formation of cyclohexanol. The photoc atalyst investigated does not suffer irreversible modifications allowi ng the oxygenation of cyclohexane by O-2 itself under mild conditions with good turnover values.