| Summary: | Includes bibliographical references (p. 177-185). === Selectivity in methylation of phenol over acidic catalysts depends primarily on temperature and the acidity of the catalyst. It is reported that direct methylation of phenol with methanol over weakly acidic catalysts yields predominantly o-cresol, whilst catalysts with medium acidity yield primarily o- and p-cresol, with significant anisole formation at lower temperatures (≈ 200°C). m-Cresol is, however, formed with significant selectivity over strongly acidic catalysts or at higher temperatures (typically 300°C and more). To date, only one industrial process is known which is selective to p-cresol but has the disadvantage of co-formaiton of inorganic salt, which is costly to dispose of.
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