Catalytic oxidation of alkylbenzenes with molecular oxygen in ionic liquids

Using ionic liquid [Hex-mim]BF₄, [Bmim]BF₄, [Bmim]PF₆, and [Omim]BF₄ as the solvent, respectively, the oxidation of alkylbenzenes by molecular oxygen was investigated under atmospheric pressure with Co (II), Mn (II), or Ni (II)/NHPI (or AIBN) as the catalysts. The [Hex-mim] BF₄/Co²⁺ (or Mn²⁺)/NHPI system was demonstrated efficient for the oxidation of alkylbenzene. Under the optimized condition, ethylbenzene, n-propylbenzene, and n-butylbenzene were oxidized to the corresponding aromatic ketone with yields up to 90%, 94%, and 93%, respectively, toluene and p-substituted toluene were oxidized to benzoic acid and the corresponding p-substituted benzoic acid with yields of 32%-47%. The ionic liquid and metal catalyst could be reused by removing water from them under a reduced pressure.