Bhaskar Sarmah

Nanocrystalline ZSM-5 based bi-functional catalyst for two step and three step tandem reactions

A Pd nanoparticle decorated nanocrystalline ZSM-5 catalyst was prepared for one-pot tandem reactions. The catalyst was characterized by the complementary combination of X-ray diffraction, N2-adsorption, electron microscopy, and NH3-temperature programmed desorption techniques. The catalyst was investigated in the one-pot tandem conversion of benzyl alcohol to 1,3-diphenyl-3-(phenylamino)propan-1-one, (E)-chalcone, and 2,3-dihydro-1,5-benzothiazepine. 1,3-Diphenyl-3-(phenylamino)propan-1-one and (E)-chalcone were prepared by two step tandem reactions from benzyl alcohol, whereas 2,3-dihydro-1,5-benzothiazepine was prepared by a three step tandem reaction from benzyl alcohol. A recycling study shows that no significant decrease in the catalytic activity was observed even after three recycles. To the best of our knowledge, this is the first report which deals with such a simple route to prepare 2,3-dihydro-1,5-benzothiazepines in a one-pot tandem methodology from benzyl alcohol.

Highly efficient and recyclable basic mesoporous zeolite catalyzed condensation, hydroxylation, and cycloaddition reactions

Crystalline mesoporous ZSM-5 zeolite was prepared in the presence of 1,4-diazabicyclo[2.2.2]octane derived multi-cationic structure directing agent. The calcined form of the mesoprous zeolite was treated with NH4OH to obtain basic mesoporous ZSM-5. Catalyst was characterized by the complementary combination of X-ray diffraction, N2-adsorption, electron microscopes, and temperature programme desorption techniques. Catalytic activity of the basic mesoporous ZSM-5 was systematically assessed using Knoevenagel condensation reaction for the synthesis a wide range of substituted styrene. Applications of the catalyst were investigated in the benzamide hydroxylation for the synthesis of carbinolamides and one-pot, multi-component condensation reaction for the synthesis of naphthopyrans. Finally, the catalyst was evaluated in the cycloaddition of CO2 to epoxide for the synthesis of cyclic carbonates. Recycling study shows that no significant decrease in the catalytic activity was observed after five recycles.

Cu ion-exchanged and Cu nanoparticles decorated mesoporous ZSM-5 catalysts for the activation and utilization of phenylacetylene in a sustainable chemical synthesis

Mesoporous ZSM-5 was synthesized using a 1,4-diazabicyclo[2.2.2]octane based multi-cationic surfactant as a structure directing agent. Cu2+ exchanged mesoporous ZSM-5 was prepared by the ion-exchange process. Cu nanoparticles decorated mesoporous ZSM-5 was prepared using NaBH4 as a reducing agent. Materials were characterized by the complementary combination of X-ray diffraction, N2-adsorption, UV-visible, and scanning/transmission electron microscopic techniques. For comparative purposes, Cu2+ exchanged ZSM-5, HY, and NaY; and Cu nanoparticles decorated conventional ZSM-5, SBA-15, and Al2O3 samples were also prepared. A sustainable catalytic process was developed for the selective synthesis of indolizine, chalcone, and triazole derivatives using a mesoporous ZSM-5 based heterogeneous catalyst. A multi-component synthetic strategy is reported here for the selective synthesis of the above mentioned chemicals that involves phenylacetylene as one of the building blocks. Control experiments were performed to ascertain the proposed reaction pathways. Recycling and leaching experiments were performed to demonstrate the sustainability and robustness of the catalytic process. Among these catalysts, Cu nanoparticles decorated mesoporous ZSM-5 exhibited the highest activity in all these reactions. The catalyst was found to be highly stable and it was possible to recycle the catalyst five times with no appreciable loss in the activity. A wide range of indolizine, chalcone, and 1,2,3-triazole derivatives were prepared in high yields using this catalyst.

One-pot tandem conversion of monosaccharides and disaccharides to 2,5-diformylfuran using a Ru nanoparticle-supported H-beta catalyst

The direct, one-pot catalytic conversion of carbohydrates (especially sucrose and glucose) to 2,5-diformylfuran is a challenging task. The development of a bi-functional sustainable heterogeneous catalyst is crucial to achieve high selectivity for the desired product 2,5-diformylfuran in this direct conversion process. In this study, tandem, one-pot, two-step direct conversion of carbohydrates into 2,5-diformylfuran is reported using a Ru nanoparticle-supported H-beta catalyst. This carbohydrate conversion process is characterized by the abundance and low cost of reactants with no need for 5-hydroxymethylfurfural separation or purification. Molecular oxygen (1 atm) is used as an oxidant. No external oxidizing reagent is required to carry out this transformation. A combination of H-beta and Ru nanoparticles successfully affords the direct synthesis of 2,5-diformylfuran from carbohydrates via isomerization, dehydration, and successive selective oxidation under one-pot conditions. This one-pot tandem reaction protocol affords 2,5-diformylfuran with yields of 80% and 67% from fructose and sucrose, respectively. Moreover, the catalyst is easily recycled and reused without any loss of catalytic activity.

An efficient halometallate ionic liquid functionalized mesoporous ZSM-5 for the reduction of carbon–carbon multiple bonds

Transition metal-containing halometallate ionic liquids (ILs)-based economical catalysts have been developed for the selective reduction of carbon–carbon multiple bonds with hydrazine hydrate in ethanol under mild reaction condition. ILs have been tethered to the surface of mesoporous ZSM-5. The Mn-based halometallate IL tethered to the surface of mesoporous ZSM-5 exhibited the best activity compared to the parent halometallate ILs. It demonstrated efficient recyclability with no appreciable loss in the catalytic activity even after being recycled five times. In order to establish the reaction mechanism, ILs-hydrazine complexes were prepared and investigated in reduction reactions. The structure–activity relationship was established by their catalytic activities, physicochemical characterizations, ILs-hydrazine complex formation, and probe reactions. The catalyst also exhibited excellent activity in the reduction of alkynes to alkanes. This catalytic process demonstrated several key advantages such as mild and convenient reaction condition, low substrate to hydrazine ratio, reusability, and the cost-effectiveness of the catalyst.

Selective Oxidation of Biomass-Derived Alcohols and Aromatic and Aliphatic Alcohols to Aldehydes with O2/Air Using a RuO2-Supported Mn3O4 Catalyst

Selective catalytic oxidation of carbohydrate-derived 5-hydroxymethylfurfural, furfuryl alcohol, and various aromatic and aliphatic compounds to the corresponding aldehyde is a challenging task. The development of a sustainable heterogeneous catalyst is crucial in achieving high selectivity for the desired aldehyde, especially using O2 or air. In this study, a RuO2-supported Mn3O4 catalyst is reported for the selective oxidation reaction. Treatment of MnO2 molecular sieves with RuCl3 in aqueous formaldehyde solution gives a new type of RuO2-supported Mn3O4 catalyst. Detailed catalyst characterization using powder X-ray diffraction, N2 adsorption, scanning and transmission electron microscopes, diffuse reflectance UV–visible spectrometer, and X-ray photoelectron spectroscopy proves that the RuO2 species are dispersed on the highly crystalline Mn3O4 surface. This catalytic conversion process involves molecular oxygen or air (flow, 10 mL/min) as an oxidant. No external oxidizing reagent, additive, or cocatalyst is required to carry out this transformation. This oxidation protocol affords 2,5-diformylfuran, 2-formylfuran, and other aromatic and aliphatic aldehydes in good to excellent yield (70–99%). Moreover, the catalyst is easily recycled and reused without any loss in the catalytic activity.