64253-31-2Relevant articles and documents
Efficient and selective oxidation of tertiary benzylic C[sbnd]H bonds with O2 catalyzed by metalloporphyrins under mild and solvent-free conditions
Hu, Meng-Yun,Liu, Lei,Qi, Bei,She, Yuan-Bin,Shen, Hai-Min,Ye, Hong-Liang
, (2020/05/19)
The direct and efficient oxidation of tertiary benzylic C[sbnd]H bonds to alcohols with O2 was accomplished in the presence of metalloporphyrins as catalysts under solvent-free and additive-free conditions. Based on effective inhibition on the unselective autoxidation and deep oxidation, systematical investigation on the effects of porphyrin ligands and metal centers, and apparent kinetics study, the oxidation system employing porphyrin manganese(II) (T(2,3,6-triCl)PPMn) with bulkier substituents as catalyst, was regarded as the most promising and efficient one. For the typical substrate, the conversion of cumene could reach up to 57.6% with the selectivity of 70.5% toward alcohol, both of them being higher than the current documents under similar conditions. The superiority of T(2,3,6-triCl)PPMn was mainly attributed to its bulkier substituent groups preventing metalloporphyrins from oxidative degradation, its planar structure favoring the interaction between central metal with reactants, and the high efficiency of Mn(II) in the catalytic transformation of hydroperoxides to alcohols.
Decatungstate catalyst supported on silica and γ-alumina: Efficient photocatalytic oxidation of benzyl alcohols
Tzirakis, Manolis D.,Lykakis, Ioannis N.,Panagiotou, George D.,Bourikas, Kyriakos,Lycourghiotis, Alexis,Kordulis, Christos,Orfanopoulos, Michael
, p. 178 - 189 (2008/09/18)
Four supported catalysts with the same tungsten loading were prepared by depositing decatungstate species W10O4-32, through wet impregnation, on the surface of γ-alumina and silica at different pH values. The prepared samples were characterized using BET measurements as well as XRD, UV-vis DR, and XP spectroscopies. Higher dispersion of W(VI) oxo-species was obtained in the silica-supported catalysts compared with the corresponding alumina-supported ones. Within the same support, the dispersion was higher when the impregnation pH is lower than the point of zero charge (pzc) of the support. The decatungstate anions were present mainly on the silica surface without any modification, whereas these underwent a partial depolymerization on their deposition on the γ-alumina surface. The extent of depolymerization was less in the sample prepared at pH above pzc. These findings were explained in terms of the mode of deposition of the W(VI) species from the solution onto the support surface. The photocatalytic activity of the aforementioned catalysts, concerning the photooxidation of 1-phenylethanol, depends on the fraction of the W10O4-32 supported species rather than on the W(VI) dispersion. Thus, extremely high conversions have been obtained over the silica-based catalysts and also over the γ-alumina-based catalyst prepared at relatively high pH. These catalysts also are very effective in the photooxidation of a series of secondary and primary benzyl alcohols, in which benzyl ketones and benzoic acids were formed as the only or major products, respectively. The easy separation of the solid catalyst from the reaction mixture, the high activity, selectivity, and stability as well as the retained activity in subsequent catalytic cycles, make these supported catalysts suitable for a small-scale synthesis. Based on product analysis and kinetic data on the heterogeneous oxidation of benzyl alcohols, we suggest that a hydrogen abstraction transfer (HAT) mechanism predominates with respect to an electron transfer (ET) one in these reactions.
