A DFT study of SN2 and E2 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 NaT3 (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 SN2 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 NaT3 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.