Inorganic hydroxide fluorides as solid catalysts for acylation of 2-methylfuran by acetic anhydride

Abstract

Several inorganic hydroxide fluorides MF n-x (OH) x with M being either aluminum, iron or magnesium were synthetized using a sol-gel method. These mesoporous fluoride materials exhibited very high specific surface areas (between 60 and 370 m 2 g -1 ) depending on the synthesis parameters used (nature of the metal, HF/Al ratio and thermal treatment). It is shown that their acidic properties can also be adjusted by tuning these parameters. Indeed, in the case of aluminum hydroxide fluorides, bi-acidic catalysts containing both Brønsted and Lewis acid sites were obtained, the amount of acid sites and the Lewis/Bronsted ratio (in the range of 1.9 to 7.6) being very dependent on the synthesis parameters. For example, the increase of the calcination temperature of aluminum hydroxide fluorides led to a decrease of both Lewis and Brønsted acid site but also an increase of the Lewis/Bronsted ratio. The most acid fluoride exhibited 542 mol g -1 of Lewis acid sites and 291 mol g -1 of Brønsted acid sites.These inorganic hydroxide fluorides were successively used as catalysts for the solventfree acylation of 2-methylfuran by acetic anhydride under mild conditions (50°C, atmospheric pressure) yielding selectively 2-acetyl-5-methylfuran. The activity of fluoride can be related to the amount of both Lewis and Brønsted acid sites. In general the higher these values, the greater the activity in acylation. A reaction mechanism was proposed involving a bi-acidic site which could be a Lewis acid site (unsaturated aluminum) in the vicinity of a Brønsted acid site.

Upgrading of furfural to biofuel precursors via aldol condensation with acetone over magnesium hydroxide fluorides MgF2−x(OH)x

“…x (OH) x exhibit tuneable acid properties, with neighbouring Lewis and Brønsted acid sites. These fluorides were successfully used as catalyst for acylation of 2-methylfuran by acetic anhydride (50 °C, atmospheric pressure) 33 and for condensation of 2,3,6trimethylhydroquinione with isophytol (100 °C, atmospheric pressure). 34 On the contrary, magnesium oxide (hydroxide)…”

Morphological effects on catalytic performance of LTL zeolites in acylation of 2-methylfuran enhanced by non-microwave instant heating

“…On the other hand, strong acid HNO3 (67 wt% or 14 M) only affords 56.4% conversion due to the presence of high water content in the concentrated acid while glacial acetic acid gives the lowest conversion (39.4%) due to its weak acidity. The catalytic activity of nanosized LTL zeolite is also compared aluminum hydroxide fluoride (AlF2.9(OH)0.1) using similar reaction conditions [51]. It is shown that AlF2.9(OH)0.1 gives the highest conversion (99.3%) with only 2-acetyl-5-methylfuran produced, indicating that this Lewis catalyst is a more efficient catalyst than nanosized LTL zeolite for acylation reaction of 2-methylfuran.…”

Preparation of PdO Doped on Bentonite as Catalyst for Friedel-Craft Acylation Reaction of Aromatic Compounds and the Investigation of the Reaction Mechanism

“…Even though, the Brønsted acid sites of the PdOAB decreased compared with AB catalyst, however, the catalytic activity was better. It was due to the presence of a higher Lewis acid sites that could stabilize the reaction intermediates [33][34][35].…”

“…From the SEM (Figure 2(f)) and XRD (Figure 3(c)) results, the tetragonal palladium oxide was located on the surface of the material, therefore increased the Lewis acid sites of the catalyst material. Many researchers reported that the catalyzed acylation reaction mechanism strongly depended on the acidity properties of the materials [15,35,37]. The AB material had higher Brønsted acid sites, therefore it showed a higher catalytic activity than the NB material and gave a higher yield toward Friedel-Craft acylation reaction.…”

“…This reaction mechanism was in agreement with the other result. Frouri et al reported that furfural acylation was facilitated by the additional Lewis sites from the alumunium(III) on the hydroxyide fluoride catalyst [35].…”