Hydroxyalkylation of aromatic compounds over protonic zeolites

Hydroxyalkylation of activated carbocyclic aromatic compounds (phenol, anisole and toluene) by a deactivated carbonyl compound such as chloral has been performed in a batch mode in the presence of different dealuminated protonic zeolites (Y-FAU, MOR, MFI and BEA). A high selectivity to the corresponding carbinols is achieved in the presence of a HBEA zeolite with a Si/Al ratio of 12.5, at 293 K. Under these reaction conditions, a high selectivity to the para isomer is obtained. Other parameters, influencing both the course of the reaction and the selectivity to the para and ortho carbinols, such as temperature, catalyst weight, Si/Al ratio, zeolite structure and substituent effects are also discussed. Finally, a study of the relative reactivities of a series of substituted arylcarbinols in the etherification reaction shows a strong influence of the electronic properties of these substituents on their stabilities. Thus, it has been shown that the presence of electron-donating groups on the carbonyl compound has to be avoided to succeed in the hydroxyalkylation reaction.