Formation Of Alkoxy Species Research Articles

A DFT study of SN 2 and E 2 reactions of butylhalides on zeolite Y: The effect of the leaving group

A density functional theory (DFT) study of adsorption and reaction of n-butyl, sec-butyl, and tert-butyl halides was carried out at B3LYP/6-311+G(d,p)//B3LYP/6-31+G(d,p) level of calculation, using a NaT 3 (T=Si, Al) cluster to represent the zeolite active site. The results show that the adsorption of the alkyl halides on the zeolite surface involves a charge–dipole interaction and is exothermic with respect to the isolated reactants, especially for butylchlorides. The formation of alkoxy species, through a S N2 type reaction mechanism, is lower in energy than proton elimination, through E2 type reaction mechanism, for the primary and secondary halides. This behavior is more accentuated for butylchlorides than for the other butyl halides. For the reactions with butyl bromides and iodides with NaT 3 cluster, the difference between the energy barriers for alkoxide formation and proton elimination is lower than for the respective chlorides. For the tert-butyl halides, proton elimination was the only reaction found possible in the calculations.

Reactivity Descriptors and Rate Constants for Acid Zeolite Catalyzed Ethylation and Isopropylation of Benzene

The acid zeolite catalyzed ethylation and isopropylation of benzene with ethene and propene is investigated at the B3LYP/6-31G* level of calculation with a T4-cluster representing the Brønsted acid site of the zeolite. After geometry optimization of reactants, transition structures, and products, a kinetic and a sensitivity analysis were used to model the reactions. These reactions proceed in one step, without formation of alkoxy species or charged intermediates. Both reaction rate constants and local HSAB properties indicate that isopropylation is favored over ethylation, in agreement with experimental observations.

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

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 SN2 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.