Catalytic acetalization of carbonyl compounds over cation (Ce3+, Fe3+ and Al3+) exchanged montmorillonites and Ce3+-exchanged Y zeolites

Abstract

Under 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 N 4-nitroacetophenone N acetophenone N 4-methoxybenzophenone N 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-nitrobenzaldehydeN benzaldehyde N 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.

Heteropolyacid-based ionic liquids as effective catalysts for the synthesis of benzaldehyde glycol acetal

“…All NMR spectra were acquired on an Avance III 500 (Bruker-Biospin) spectrometer using a single-pulse sequence and operating at a Larmor frequency of 500. 13 [38][39][40][41][42][43][44][45]. It has been demonstrated that a linear correlation between the observed 31 P NMR chemical shifts and the strengths of Brønsted acidity may be inferred [50,51] by means of such 31 P-TMPO NMR approach.…”

“…In addition, acetalization carried out over these acid catalysts also suffered from inherent problems such as highly susceptible to water and excessive amounts of by-products. As such, considerable efforts have been made in developing more durable solid acid catalysts for acetalization of aldehyde with alcohol, for examples, supported Lewis acid [10][11][12], zeolites [13,14], montmorillonites [5,15], and ion exchange resins [16][17][18]. Nonetheless, issues related to product selectivity, environmental safety, spent catalyst disposal, and catalyst recyclability remained as critical challenges for the design and fabrication of highly active catalysts for acetalization.…”

“…MHz for the 1 H,13 C, and 31 P nucleus, respectively. All [PPSH] x H 3−x PW 12 O 40 (x = 1.0-3.0) IL catalysts exhibited similar high-resolution (solution-state) 1 H and 13 C NMR spectra in D 2 O.…”

Nanoscale zero valent supported by Zeolite and Montmorillonite: Template effect of the removal of lead ion from an aqueous solution

“…On the other hand, Montmorillonite, is one of the most expandable minerals (Clay 2:1) characterized by its laminar organization, consisting of two tetrahedral layers of silica and a central octahedral layer of aluminum oxide [21,[25][26][27][28]. Both possess a negative charge as a consequence of the isomorphous substitution process, providing a high cation-exchange capacity of ions [23][24][25][26][27][28][29][30]. In addition, the high porosity of clay is widely used in the removal of metallic ions present in aqueous solutions.…”

“…In addition, the high porosity of clay is widely used in the removal of metallic ions present in aqueous solutions. This process occurs following two mechanisms: cation exchange (charge effect) and the formation of inner sphere complexes, due to the ionization of surfaces silanol sites ( Si OH) and aluminols ( Al OH) [18,29,30].…”