Metal cation-exchanged montmorillonite (Mn+-mont)-catalysed aromatic alkylation with aldehydes and ketones

Abstract

The alkylation of aromatic compounds with aldehydes and ketones in the presence of a variety of metal cation-exchanged montmorillonites (Mⁿ⁺-mont; Mⁿ⁺ = Zr⁴⁺, Al³⁺, Fe³⁺, Zn²⁺, H⁺, Na⁺) has been investigated. Al³⁺- and Zr⁴⁺-Monts are revealed to be effective as catalysts, while no reaction takes place with Na⁺-mont. Al³⁺-Mont-catalysed alkylation of phenol with several aldehydes produces mainly or almost solely the corresponding gem-bis(hydroxyphenyl)alkanes (bisphenols) in good yields, while that with several ketones affords selectively the corresponding alkylphenols in moderate to good yields. The alkylation always occurs at the carbonyl carbon without any skeletal rearrangement and the kind of products depends much on the steric hindrance of an electrophilic intermediary carbocation. The alkylation of anisole, veratrole and p-cresol proceeds well, while that of toluene, benzene, chlorobenzene and nitrobenzene scarcely occurs.