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Ramu, Vasanthakumar Ganga
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article
Catalytic acetalization of carbonyl compounds over cation (Ce3+, Fe3+ and Al3+) exchanged montmorillonites and Ce3+-exchanged Y zeolites
Abstract
nder ambient reaction conditions, a one-pot acetalization of carbonyl compounds with methanol was carried out over a series of solid acid catalysts. Ion-exchanged montmorillonite samples were prepared by a metal cation (Ce 3+ , Fe 3+ and Al 3+ ) exchange from the activated K-10 montmorillonite. These materials have been characterized by wide-angle X-ray scattering (WAXS), solid-state nuclear magnetic resonance spectroscopy (solid-state NMR) , temperature programmed desorption of ammonia (NH 3 -TPD) and Brunauer–Emmett–Teller (BET) analysis. The catalytic results of montmorillonites were compared with those of H–Y, Ce,Na–Y, Ce,H–Y zeolites, SiO 2 and γ-Al 2 O 3 . Irrespective of the catalyst, the reaction yields the corresponding dimethoxyacetal in high yield. Comparison of the catalytic activity indicates that the montmorillonite catalysts are the most active catalysts for the reaction. The molecular size of the carbonyl substrates is one of the significant factors in determining the acetalization ability of the catalysts, and the activity of ketones follow the order cyclohexanone > 4-nitroacetophenone > acetophenone > 4-methoxybenzophenone > benzophenone. In the aromatic carbonyl compounds, the electron donor or acceptor properties of the substituents are also critical to the reactivity of the acetophenones and benzaldehydes. The aldehydes considered in the present investigation exhibit an activity order of 4-nitrobenzaldehyde > benzaldehyde > 4-methoxybenzaldehyde, which substantiates that electron-withdrawing groups favor the reaction. The reaction time studies indicate that the montmorillonite catalysts are more resistant to deactivation, predominantly due to the superior pore diffusional properties of these materials compared to microporous zeolites.