Room temperature acetalization of glycerol to cyclic acetals over anchored silicotungstates under solvent free conditions

Abstract

Heterogeneous catalysts comprising of parent Keggin type silicotungstate as well as monolacunary silicotungstate anchored to MCM-41 were synthesized and characterized by several physicochemical methods. A solvent free green route towards valorisation of glycerol via acetalization with benzaldehyde has been proposed. Both the catalysts showed very good activity as well as selectivity towards dioxolane derivatives within a short reaction time and at room temperature. The tuning of the acidity of the parent silicotungstate leads to an increase in the selectivity towards 1,3-dioxolane. The catalysts were also recycled up to four times without any significant loss in the conversion. The excellent performance of these mesoporous catalysts is attributed to their combination of acidity, wide pores and large specific surface area.

ab initio Method on the Mechanism of Acetalization of 2-Methoxybenzaldehyde Using Halogen Acid Catalysts

“…Reaction mechanism: There is a two-step process to produce acetal product. The first is the formation of a hemiacetal (3). The mechanism is started from protonation of carbonyl by the Brønsted acid (H + ions of the acid catalyst) because there is a weak nucleophile in benzaldehyde compound and produce compound 1.…”

“…Acetals were usually synthesized from carbonyl compounds such as benzaldehyde with an alcohol that catalyzed by an acid catalyst as shown in Scheme-I [2]. So far, a few catalysts such as MCM-41 [3], indium triflate [4] and NCS/ thiourea [5], H4[SiW12O40]/SiO2 [6], mesoporous metal-organic framework MIL-100(Fe) [7], aluminium and thiourea containing MOF [8,9], MOF MIL-101 bearing sulfonic acid groups [10], metal-organic frameworks (MOFs) based on the UiO-66(Zr) structure [11], copper, iron, zeolite beta [12], benzimidazolium cation [13] and UIO 66 catalyst [14] have a function as catalyst in the acetalization of benzaldehyde.…”

Facile synthesis of glycerol carbonate via glycerolysis of urea catalysed by silicotungstates impregnated into MCM-41

“…[25][26] The main characterization of the catalysts such as BET, FT-IR, XRD, 29 Si-MAS-NMR, and n-butyl amine acidity are given for readers'…”

“…[25][26] In continuation of our previous efforts to explore wider applicability of these catalysts for acid catalysed organic transformations, for the first time, we report synthesis of GlyC over SiW 12 as well as SiW 11 impregnated to MCM-41. The effect of different reaction parameters was studied for maximum conversion.…”

Theoretical Study on the Reaction Mechanism of Acetalization of 3-Chlorobenzaldehyde Catalyzed by Halogen Acid

“…Acetalization of 3-chlorobenzaldehyde is carried out between 3-chlorobenzaldehyde and an alcohol wherein acid is used as the catalyst as shown in Scheme 1. Currently, some acid catalysts have been successfully in the acetal formation include HCl, HBr, H4[SiW12O40]/SiO2 [1], Mesoporous metal-organic framework MIL-100(Fe) [2], metal copper, iron, zeolite beta [3], and benzimidazoliumcation [4].The utilization of acid catalysts such as benzimidazolium-organic frameworks (MOFs) based on the UiO-66(Zr) structure [5], aluminium and thiourea containing MOF [6] [7], MOF MIL-101 bearing sulfonic acid groups [8], MCM-41 [9], indium triflate [10] and NCS/thiourea [11], cation catalyst, Cu3(BTC)2, and UIO 66 catalyst in the acetalization of benzaldehyde showed a good catalytic activity (>88%) [4][6] [12].Acetal is known to be useful as fragrances in cosmetics, food and beverage additives, pharmaceuticals, solvents, detergents, drug design, carbohydrate chemistry, intermediates or finalproducts in petrochemicals, and in lacquer industries [13].…”