Thymol synthesis by acid catalysed isopropylation of m-cresol
The initial motivation for this study was to identify a suitable window of operation for thymol synthesis from iso-propanol and m-cresol mediated by a commercially available H-MFI zeolite catalyst. A preliminary investigation uncovered seeming anomalies in the course of the synthesis process, in particular counterintuitive trends with respect to m-cresol conversion and thymol selectivity at low space velocity. Consequently, the study sought to establish the reaction pathway responsible for these observations in an attempt to gain an understnding for future thymol yield optimisation studies. Under the reaction conditions studied, complete dehydration of iso-propanol was observed. Further reaction of the propene to olefinic species with carbon numbers higher than 3 was also seen. Results showed that the cause of the so-called “volcano curve” in respect of m-cresol conversion was found in the system’s propensity for the formation of cresylic rings which were alkylated with side chains consisting of carbon atoms between 4-8, particularly under severe reaction conditions. This fraction was formed via the alkylation of the m-cresol with the said olefinic pool. The thymol synthesis system was also found to be thermodynamically limited at high reaction temperature and low space velocity
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