Selective oxidations of allylic alcohols with H2O2 on a series of lanthanide decatungstate modified with 1-hexadecylpyridinium cation [{C5H5N(CH2)15CH3}7H2Ln(III)W10O36;: cetyl-LnW10, Ln:La-Er]:: kinetic features and working mechanisms

Selective oxidation of 1-octen-3-ol to 1,2-epoxy-3-octanol and 1-octen-3-on with H2O2 catalyzed by {C5H5N(CH2)(15)CH3}(7) H2Ho(III)W10O36(cetyl-HoW10) in a CHCl3-H2O2 aqueous biphasic system, adapted as a test catalytic reaction, was kinetically investigated. The rate equations for the epoxide and enon formation were successfully described by equations: R-epoxy = k(1.epoxy) [substrate] [H2O2](1.6), and R-enon = k(1.enon) [substrate] [H2O2](-0.6). A working mechanism in which H2O2 molecule acts additionally to the substrate molecule which has been activated by interaction with a peroxo-species formed on the cetyl-LnW10 catalyst was proposed the H2O2 molecule promotes the epoxide formation, but suppresses the enon formation. 2-Hexen-1-ol was easily oxidized in the catalyst system, although 2-octene without a terminal OH-group was not. Moreover, the activity decreased drastically as the olefinic-group was far away from the terminal position. These results indicate that the terminal OH-group plays an important role in the activation of the substrates. The working state and the activity of catalyst were greatly influenced by the polarity of the solvent used. Especially, in the organic solvent-free system, the activity was very much promoted. Thus, cetyl-LnW10 is a suitable catalyst, from the environmental viewpoint. With the oxidations of both 1-octen-3-ol and 2-hexen-1-ol catalyzed by a series of Ln(III)W10; Ln: La-Er, the activities varied regularly according to the tendency of contraction of the Ln(III) ion. Those findings were interpreted reasonably by the mode of interaction and the working mechanism postulated, and clearly support the proposal that the 4f(n)-electrons of the Ln(III) ion participate in the catalysis. (C) 2002 Elsevier Science B.V. All rights reserved.