FT-IR Investigation of Methoxy Substituted Benzenes Adsorbed on Solid Acid Catalysts

The nature of the interaction on two different catalysts (zeolite BEA and
γ-alumina) of some aromatic substrates, 1,2-methylendioxybenzene, 1,2-ethylendioxybenzene,
and 1,2-dimethoxybenzene, have been investigated by FT-IR spectroscopy.
FT-IR data suggest that the adsorption of 1,2-methylendioxybenzene occurs through
oxygen atoms and the molecule maintains the original puckered conformation, whereas
the planar structure due to the absence of a fused ring in the case of 1,2-
dimethoxybenzene and the twisted conformation of 1,2-ethylendioxybenzene cause an
orientation of the molecules parallel to the catalyst surface, with the benzene ring
directly interacting to it. The puckered conformation of MDB leads the benzene ring to
be electron-deficient, then deactivated toward alkylation, such as confirmed by the obtained catalytic results, which show that
MDB is totally not reactive using the investigated heterogeneous catalysts, while in the traditional homogeneous system shows a
reactivity comparable to the other considered substrates.