PLS versus zeolites as sorbents and catalysts: Part 9. An unexpected reaction of Al-PILC sorbed CCl4 with benzene

Reactivity of CCl4 on alumina-pillared clays (PILCs) has been exploited to investigate if benzene activation is possible under both static and dynamic conditions. PILC-encapsulated CCl4 indeed reacts, giving chlorobenzene (PhCl) and biphenyl as main products (with benzoyl chloride as a side-product). Although overall yields are low (2–4%, calculated on starting benzene) they increase when a transition metal-containing pillar is present (e.g. FAZA, which has Fe2+/Fe3+-alumina pillars and activity comparable with the mid-pore zeolite ZSM-5). Yields increase further (e.g. PhCl > 5%) when the PILC is also cation-exchanged, as in Cu-FAZA. Trends in yields on changing reaction parameters show that the reaction giving PhCl occurs via a cation-intermediate, whereas biphenyl is formed via a free-radical mechanism. Finally, chlorohydroxybenzenes can be obtained in both mid-pore zeolites and PILCs, which is rationalised in terms of generation of active oxygen species at the Lewis acid sites. It is suggested that benzoyl chloride forms from interaction between in situ-generated COCl2 and Lewis acid sites.