E. Kozhevnikova, J. Quartararo, I. Kozhevnikov
May 30, 2003
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0
Influential Citations
52
Citations
Journal
Applied Catalysis A-general
Abstract
Abstract Heteropoly acids (HPAs) are active catalysts for the Fries rearrangement of aryl esters (phenyl acetate, phenyl benzoate, and p-tolyl acetate) to yield the acylated phenols and esters together with phenols in homogeneous or heterogeneous liquid-phase systems at 100–170 °C. Amongst the HPA catalysts studied are bulk, silica-supported, and sol–gel silica-included H3PW12O40 (PW), as well as bulk Cs+ and Ce3+ salts, Cs2.5H0.5PW12O40 and Ce0.87H0.4PW12O40. The reaction with bulk and silica-supported PW occurs homogeneously in aryl esters (without solvent) or in polar solvents, such as nitrobenzene and o-dichlorobenzene. In non-polar solvents such as dodecane, the reaction is heterogeneous. The Cs+ and Ce3+ salts and sol–gel PW catalysts perform heterogeneously in all these media. From heterogeneous systems, the catalysts can be separated and reused, albeit with reduced activity. The homogeneous and silica-supported PW are much more active than H2SO4 and H-Beta zeolite, which is explained by the greater acid strength of HPA compared to the other acids. In contrast to silica-supported PW, the sol–gel PW catalysts show only a negligible activity in the Fries reaction of phenyl acetate, yielding mainly phenol with 92–100% selectivity. This may be explained by a weaker acid strength of the sol–gel catalysts and the presence of relatively high amount of water. 31 P MAS NMR shows that the state of the PW anion in the sol–gel and silica-impregnated catalysts is similar, but different from that in the bulk PW.