ABSTRACT

       In this Ph.D thesis, we have investigated the reaction mechanism of the acylation of aromatic substrates with acylating agents, using as catalysts zeolites with different topology. The combination of in situ solid-state NMR spectroscopy and theoretical calculations has allowed the identification of the intermediates formed by reaction of the acylating agents (acetyl chloride, acetic acid and acetic anhydride) with the zeolite Brønsted acid sites. The results obtained show that small pore zeolites are less active in the acylation of anisole, probably because of diffusion constraints through the zeolite pore system. Moreover, we have observed that the reaction product, p-methoxyacetophenone, remains strongly adsorbed on the Brønsted sites contributing to catalyst deactivation.
       This methodology has been also applied to investigate the Beckmann rearrangement reaction over zeolites and mesoporous materials with active sites of different nature, Brønsted acid sites with varying acidic strength, and silanol groups. Because the industrial process, special attention has been paid to give evidence that the Beckmann rearrangement of cyclohexanone oxime into ?-caprolactam occurs, at least in part, in the interior of the pores of MFI zeolites, and that the active sites located on the external zeolite surface are less active than the internal ones.
       We have also investigated the Beckmann rearrangement in different ionic liquids (ILs): 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate and 1-butyl-4-methylpyridinium hexafluorophosphate, using different analytical and spectroscopic techniques, such as in situ solid-state NMR spectroscopy. The results obtained give evidence that the presence of water, even the traces present in dry ionic liquids, has a strong influence on the catalytic activity as it can hydrolyze PF6- in 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-4-methylpyridinium hexafluorophosphate ILs producing HF, which is already able to catalyze the Beckmann rearrangement of cyclododecanone oxime to ?-laurolactam with good activity and selectivity, even at the level of ppm.
       The results obtained in the Beckmann rearrangement reaction of oximes in ILs, motivated us to investigate the influence of water on the nano-structural organization of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium tetrafluoroborate, with different miscibility with water. Intermolecular interactions in these ILs have been studied by applying solution-state NMR techniques, such as DOSY, ROESY and NOESY. The results obtained indicate that BF4- interacts stronger with water than PF6-, and that the contacts of PF6- with the imidazolium cations are less selective.