Kinetic study and reaction mechanism of the hydroxyalkylation of aromatic compounds over H-BEA zeolites

Abstract

Hydroxyalkylation of various carbocyclic aromatic compounds has been carried out in the presence of dealurninated H-form BEA zeolites. A kinetic study has been realized by varying several reaction parameters such as catalyst weight, initial concentration in aromatic reactants, temperature, substituent effects on aromatic substrates. The experimental results obtained allowed to propose a ‘poisoned Eley–Rideal’ reaction mechanism, where the adsorbed aromatic substrate does not react with a molecule of chloral, but acts as a poison of the reaction. The ratio of the adsorption constants of the two reactants has been determined. Anisole was found to be more strongly adsorbed than chloral. Moreover, it has also been shown that this electrophilic aromatic substitution reaction follows a Hammett-type correlation, with a strong negative ρ-value of −4. The presence of a strong electron-donating substituent on the aromatic ring not only increases the reaction rate, but also favors the formation of the undesired bisarylalkanes.