Selective alkylation of toluene over basic zeolites: an in situ infrared spectroscopic investigation

In situinfrared spectroscopy was used to study the sorption and reaction of toluene and methanol over various alkali exchanged X zeolites. The size of the metal cations controls the preference of sorbing methanol or toluene. The smaller the cation, the higher the preference for methanol is. A balanced sorption stoichiometry of the reactants, the intermediate conversion of methanol into formaldehyde and the strong polarization of the methyl group of toluene are critical to catalyze side chain alkylation of toluene. These requirements are best met with very basic zeolites such as the Cs-X and Rb-X

Alkylation of Toluene over Basic Catalysts—Key Requirements for Side Chain Alkylation

In situinfrared spectroscopy was used to study sorption and reaction of toluene and methanol over various basic catalysts (MgO, hydrotalcites, and basic zeolites). The size of the metal cations controls the preference of sorbing methanol or toluene; i.e., the larger the metal cation, the higher the preference for toluene. The key requirements for a good catalyst for side-chain alkylation are (i) sufficient base strength to dehydrogenate methanol to formaldehyde, (ii) stabilization of sorbed toluene and polarization of its methyl group, and (iii) balanced sorption stoichiometry of the two reactants. The formation of the carbon–carbon bond mechanistically resembles an aldol condensation