SN2, E2 reactions of butylchlorides on NaY zeolite: A potential method for studying the formation and reactivity of alkoxy species on the zeolite surface

Abstract

The adsorption and reaction of n-butyl, sec-butyl, isobutyl and tert-butyl chlorides over NaY zeolite was studied by infrared spectroscopy. All the chlorides reacted almost instantaneously with the zeolite, giving rise to CH₂ and CH₃ bands in the infrared spectra. A band at approximately 1640 cm⁻¹, ascribed to CC vibration, was observed in all experiments, its intensity being dependent upon the structure of the chloride. For tert-butyl chloride the intensity is greatest, and bands at 3550 and 3061 cm⁻¹, ascribed to the acidic OH and olefinic CH, respectively, were observed. The intensity of the olefinic band is weaker in secondary and especially primary chlorides. Calculations at the B3LYP/6-31+G** level, using a T₃ cluster to represent the zeolite active site, indicated that, for the secondary and primary chlorides, the formation of the alkoxy species, through an S_N2 type reaction mechanism, is lower in energy relative to proton elimination, through an E2 type mechanism. The opposite was observed for the tert-butyl chloride, in agreement with the experimental results. The method can be useful for generating alkoxide species, especially primary and secondary ones, and for studying their reactivity on the zeolite surface.