Hydrophobicity and co-solvent effects on Meerwein-Ponndorf-Verley reduction/dehydration cascade reactions over Zr-zeolite catalysts

Trans-anethole is an important ingredient in many flavors, fragrances and pharmaceutical formulations. Heterogeneous catalysis provides the opportunity for its green synthesis from 4'-methoxypropiophenone via a cascade of Meerwein-Ponndorf-Verley reduction followed by dehydration. Zr-containing zeolites were especially active catalysts. Surprisingly, Zr-HY was more active than Zr-Beta or mesoporous ZrMSU. The effect of pore size, hydrophobicity and co-solvent has been investigated. Pyridine poisoning revealed that weak Lewis acid sites can catalyze the MPV reduction but stronger acid sites are required for the dehydration. The hydrophobicity and the ratio of open/closed Zr sites were higher for Zr-HY than Zr-Beta. Adding a moderately polar co-solvent like p-xylene more than doubled the reaction rate compared to only 2-pentanol as solvent. For an efficient cascade reaction, a hydrophobic catalyst with large micropores is required which combines hydrogen transfer and dehydration activities, together with an inert co-solvent that balances the concentration of both substrates inside the zeolite. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

Heterogeneous catalysis using Zr-containing zeolites allows for the green synthesis of trans-anethole from 4'-methoxypropiophenone via a cascade of Meerwein-Ponndorf-Verley reduction followed by dehydration. Zr-HY was found to be more active than other catalysts, with the impact of solvent and acidity levels also being investigated.