Spectroscopic and kinetic study of the alkylation of phenol with dimethyl carbonate over NaX zeolite

Abstract

The interaction of phenol and dimethyl carbonate (DMC) with acid–base sites in zeolite NaX has been studied using FTIR, UV and mass spectroscopy. At room temperature, phenol is predominantly adsorbed by hydrogen bonding to basic oxygen atoms of NaX. At higher temperature, phenol is partially deprotonated over basic sites to form phenolate anions; the latter undergo H-bonding to zeolitic hydroxy groups and Na⁺ ions. DMC forms a chelating complex with Na⁺ ions at room temperature which decomposes at 150°C into dimethyl ether and CO₂. FTIR experiments of coadsorbed reactants show that, in the presence of phenol, DMC is mainly bonded by its carbonyl oxygen to Lewis acid sites. The formation of anisole sets in at 150°C and proceeds presumably via nucleophilic attack at the methyl carbon of DMC by the oxygen atom of H-bonded phenol or phenolate. Kinetic measurements reveal that the reaction order is negative in phenol but positive in DMC pointing to site blocking by strongly adsorbed phenol.