The Beckmann rearrangement catalyzed by silicalite: a spectroscopic and computational study

摘要

The rearrangement of cyclohexanone oxime to caprolactam over zeolites withrnMFI and FAU structure is investigated by means of spectroscopical (IR) andrncomputational methods. Infrared spectroscopy is used to investigate the diffusionrnof the reactant into the zeolite, its interaction with acid sites and itsrnrearrangement. The main species participating in the reaction are identified, forrnfurther theoretical study. Hydrogen bond interaction, proton transfer andrnrearrangement are detected. As a guideline for the determination of thernmechanism, the thermal reaction mechanism and that catalyzed by H~+ arerninvestigated by means of quantum chemical methods at the B3LYP/6-31+G(d,p)rnlevel of theory. Subsequently, the interaction of the reactant, products andrntransition state structures with HCl, and silanol are studied in order to model therneffect of acids of different strenght on the reaction mechanism. The H+-catalyzedrnmechanism is found to be a multi-step mechanism in which internal protonrntransfer from N to O in the oxime is the rate determining step. On the contrary, inrnpresence of weaker acids, a single-step mechanism similar to that of the thermalrnreaction is found, and the activation energy is correlated with acid strenght.