Aerobic oxidation of cyclohexane using N-hydroxyphthalimide bearing fluoroalkyl chains

The N-hydroxyphthalimide derivatives, F(15)- and F(17)-NHPI, bearing a long fluorinated alkyl chain, were prepared and their catalytic performances were compared with that of the parent compound, N-hydroxyphthalimide (NHPI). The oxidation of cyclohexane under 10 atm of air in the presence of fluorinated F(15)- or F(17)-NHPI, cobalt diacetate [Co(OAc)(2)], and manganese diacetate [Mn(OAC)(2)] without any solvent at 100 degrees C afforded a mixture of cyclohexanol and cyclohexanone (K/A oil) as major products along with a small amount of adipic acid. It was found that F(15)- and F(17)-NHPI exhibit higher catalytic activity than NHPI for the oxidation of cyclohexane without a solvent. However, for the oxidation in acetic acid all of these catalysts afforded adipic acid as a major product in good yield and the catalytic activity of NHPI in acetic acid was almost the same as those of F(15)- and F(17)-NHPI. The oxidation by F(15)- and F(17)-NHPI catalysts in trifluorotoluene afforded K/A oil in high selectivity with little formation of adipic acid, while NHPI was a poor catalyst under these conditions, forming K/A oil as well as adipic acid in very low yields. The oxidation in trifluorotoluene by F(15)- and F(17)-NHPI catalysts was considerably accelerated by the addition of a small amount of zirconium(IV) acetylacetonate [Zr(acac)(4)] to the present catalytic system to afford selectively K/A oil, but no such effect was observed in the NHPI-catalyzed oxidation in trifluorotoluene.