Sulfuric Acid Immobilized on Silica Gel as Highly Efficient and Heterogeneous Catalyst for the One-Pot Synthesis of 2,4,5-Triaryl-1H-imidazoles

Abstract

Application of sulfuric acid immobilized on silica gel as an efficient and benign catalyst has been explored in the syn-thesis of 2,4,5-Triaryl-1H-imidazoles via condensation reaction of benzil or benzoin, aldehyde and ammonium acetate. The key advantages of this process are high yields, cost effectiveness of catalyst, easy work-up, purification of products by non-chromatographic method and the reusability of the H<sub>2</sub>SO<sub>4</sub>.SiO<sub>2</sub> catalyst

Nano silica boron sulfuric acid as a dual Brønsted/Lewis acid and a heterogeneous catalyst in Baeyer–Villiger oxidation of ketones with hydrogen peroxide

“…We can also notice that aromatic ketones have reacted slowly, but in phenyl rings, those containing EDGs (Entries 14,15,18), the yields of products are little enhanced, because of the electron donating character of the substituents to lessen the Criegee transition state energy level in comparison with rings without any substituents or vice versa rings containing EWGs, which is in agreement with previous observations and literature reports [4,28].…”

“…So, two more practical strategies applied to overcome its drawbacks: (i) applying an acidic catalyst to improve the electrophilicity of the carbonyl group of ketone to compensate the weakness of the nucleophilicity of hydrogen peroxide, (ii) using a base to deprotonate or polarized the O-H bonds of hydrogen peroxide to improve its nucleophilicity toward the carbonyl group of ketone. In recent years, heterogeneous catalysts, chiefly solid acids and especially those based on micelle-templated silica and other mesoporous high surface area support materials, play a more serious roles in acid-catalyzed chemical transformations because of their good catalytic activities, high efficiency and selectivity, reusability, simple separation from the reaction mixture and also less environmentally impacts, as important principles of green chemistry [16][17][18][19][20][21][22]. It is shown that nano silica boron sulfuric acid (NSBSA), which is considered as a dual Brønsted/Lewis acid and also an eco-friendly nano-heterogeneous catalyst, has an effective role in performing acid-base catalyzed organic transformations [22].…”

Ketalization of Ketones to 1,3-Dioxolanes and Concurring Self-Aldolization Catalyzed by an Amorphous, Hydrophilic SiO2-SO3H Catalyst under Microwave Irradiation

“…The SiO 2 -SO 3 H catalysts can be prepared in several ways. Examples range from the simple addition of H 2 SO 4 to slurries of silica and ether 2,3 or the treatment of silica with chlorosulfonic acid 4 to more complex synthesis of mesoporous materials where the sulfonic groups are separated from the surface of the silica by carbon chains. 5 This method is also a form of diminishing the hydrophilicity of the catalyst.…”

“…6 We recently developed a mesoporous, sulfonated silica as a Brønsted acid, whose high hydrophilicity made it ideal for the catalysis of waterforming, proton-assisted organic transformations, such as the formation of ethers from alcohols and the esterification of acids with alcohols, equations 1 and 2. 7 SiO 2 -SO 3 H 8 and SiO 2 -(CH 2 ) 3 -SO 3 H 6 have been reported to catalyze ketal formation from ketones and ethylene glycol, which is also a water-forming reaction involving the equilibrium shown in equation 3.…”

Silica sulfuric acid: a reusable solid catalyst for one pot synthesis of densely substituted pyrrole-fused isocoumarins under solvent-free conditions

“…The high catalytic activity, the operational simplicity and the recyclability of SSA can be exploited in the industry for the synthesis of various drugs and pharmaceuticals. SSA, a product that is easily synthesized from silica gel and chlorosulfonic acid [26], was observed to improve the reactivity and selectivity in carbon–carbon bond-formation reactions [27–28], in cycloaddition reactions [29–30], in protection–deprotection reactions of multistep syntheses [31–33], in esterifications [34] and in syntheses of heterocycles [35]. Since we are actively involved in the synthesis of biologically important heterocycles [36–42], we wish to report herein a green methodology for the construction of pyrrole-fused isocoumarins, which uses SSA as a solid-supported acid catalyst under solvent-free conditions (Scheme 1, present work).…”