Alkylation of Phenols. II. The Selective Formation of Thymol from m-Cresol and Propylene with a γ-Alumina Catalyst

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The alkylation of m-cresol with propylene was carried out over a γ-alumina catalyst in a flow system under atmospheric pressure. It was found that the composition of the thymol mixture thus obtained was greatly ortho-rich. It was also observed that the catalytic activity varied with the temperature and the atmosphere for the calcination of the catalyst, whereas the selectivity for thymol formation was almost constant at about 90% at the reaction temperature of 250 °C. It has been established that thymol can be obtained selectively by vaporphase alkylation over a commercial γ-alumina catalyst under appropriate reaction conditions. Furthermore, the active sites of γ-alumina for this reaction were investigated by the poisoning technique with acids and bases. It was suggested that, for the alkylation, the Lewis-acid sites (surface aluminum) and the adjacent acid sites (surface hydroxyl) are necessary. The mechanism of the alkylation on those sites is also discussed.
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