Current Catalysis - Volume 10, Issue 2, 2021

Synthesis of chalcone by Claisen–Schmidt condensation using recyclable L- aspartic acid coupled with imidazolium-based ionic liquid as a green synthetic approach has been developed. Present work offers significant advantages, such as high yield, enhanced reaction speed even at room temperature, catalyst reusability, and the involvement of non-toxic reagents. Background: Chalcones belong to the flavonoid family and possess pharmacological and biological activities, including antibacterial, antifungal, immunosuppressive, and anti-nociceptive properties. Objective: Ionic liquids have emerged as powerful tools for molecular organic solvents. Their wide liquid range, easy recovery, and reusability make them a greener alternative to volatile organic solvents. Thus, in the present work, our objective was to employ them as dual catalysts and solvent systems for the synthesis of chalcone via the CS condensation. Methods: In a typical experiment, benzaldehyde (10 mmol), acetophenone (10 mmol), and 2.5 mol% (L-AAIL) ionic liquid were mixed in a 50 mL round-bottom flask. The reaction was proceeded quickly at room temperature with stirring, and the resulting mixture became a biphasic system with the precipitate at the bottom and the upper phase containing some unreacted substrate which was separated from the catalyst by filtration and decantation. The catalyst was extracted with CH2Cl2 and separated for the next cycle. Results: Claisen–Schmidt condensation accomplished with reasonable to good yields, ranging from 78 to 95% at room temperature in presence of the [L-AAIL], as compared to the traditional route at more than 100°C. Conclusion: [L-AAIL] is found a highly efficient and eco-friendly catalyst for the synthesis of chalcone derivatives at room temperature. [L-AAIL] as a solvent and catalyst will exhibit real advantages by providing a ‘green’ process with a safer operation. Furthermore, short reaction periods, mild reaction conditions, easier separation, and reusability of ionic liquid made this methodology valuable for synthetic organic chemists as well as industry.

Background: A mathematical model for the combustion of ethanol and ethyl acetate mixtures using Mn9Cu1 (mixture of manganese and copper with a weight ratio of 9:1) catalyst is discussed. The model’s kinetic mechanism is expressed in terms of nonlinear reaction-diffusion equations with common initial and boundary conditions in a finite planar, cylindrical, and spherical geometry. A Taylor series approach is used to derive general approximate analytical expressions of ethanol, acetaldehyde, and ethyl acetate molar concentrations inside the particle and reactor phase for various values of rate constants, diffusion, and kinetic parameters. The effect of shape factor for the planar, cylindrical, and spherical geometry of dispersed particles was examined for the first time. Activation energy and rate constant at the reference temperature of ethanol, acetaldehyde, and ethyl acetate are also obtained from the rate equations. A direct comparison with numerical simulations confirms the accuracy of the derived analytical results. Objective: Derive general approximate analytical expressions of ethanol, acetaldehyde, and ethyl acetate molar concentrations inside the particle and reactor phase for various parameter values. Methods: We employ the simple and reliable Taylor series method. Results: Semi-analytic expressions of the concentration and bulk concentration of ethanol, ethyl acetate, and acetaldehyde. Conclusion: Approximate analytical expressions of the concentrations of ethanol, acetaldehyde and ethyl acetate were derived for arbitrary catalyst particle (planar, cylindrical and spherical) by using a simple, reliable, and robust method. In addition, the concentration of the species in reactor phase was also reported. The effects of the kinetic parameters, which are influenced by adsorption equilibrium constant, effective diffusivity, activation energy, on concentration, were discussed.

Background: Biodiesel has been shown to be effectively produced by immobilized enzymatic catalysts. The selection of support material is a prominent factor for obtaining an efficient lipase. Silk fibroin (SF) is a natural polymer produced by glands of some arthropods, especially by the Bombyx mor, attracting attention for immobilization of lipase. Objective: This paper presents a novel method to obtain silk microfibers (SMF) from Oxone® salt in water, used as support for Amano AK lipase from Pseudomonas fluorescens in biodiesel production from deodorization distillate of palm oil (DDPO). Method: The oxone® salt in the presence of Ca2+ ions acts as a mineralizing agent in the peptide bonds present in silk fibroin, altering some of its physical and chemical properties, such as zeta potential, crystallinity, micro-morphology, infrared spectroscopic profile, and showing formation or absence of SF original connections. Results: The modified support was tested as a support alternative for the immobilization of Amano AK lipase from Pseudomonas fluorescens. Enzyme activity values indicated that lipase immobilization on SMF was efficient as a heterogeneous catalyst in the esterification of DDPO (deodorization distillate palm oil). Conclusion: The effect of some reaction parameters, such as catalyst concentration, molar ratio, temperature, and reaction time, was studied to optimize the conditions for maximum conversion of DDPO (40.5%).

Background: Metal oxide itself and metal oxide nanoparticles are gaining significant importance due to their reusability and wide range of catalytic applications in many organic transformations. Objective: This study aimed to report a simple and efficient Fe3O4catalyzed one-pot fivecomponent reaction protocol for the synthesis of novel thiophene containing aminonaphthols under solvent-free conditions. Methods: To prepare the Fe3O4 nanoparticles by facile and simple co-precipitation method, surface characterization was done using FT-IR, XRD, BET, SEM, and TEM analysis techniques. Aminonaphthol derivatives bearing thiophene moiety were synthesized using Fe3O4 nanoparticles under solvent-free condition. Results: The prepared nanoparticles are smaller in size (15nm) and can be easily separated. They can be recycled and reused five times without any significant loss of catalytic activity with excellent yields in short time. The existing protocol for the synthesis of aminonaphthols becomes feasible and attractive due to reusability of catalyst, excellent catalytic performance, and eco-friendly procedure. Conclusion: In conclusion, Fe3O4 nanoparticles provide a simple, efficient and greener one-pot five component synthetic approach for the synthesis of thiophene containing aminonaphthols. Excellent catalytic activity was perceived in short reaction time without any co-catalyst or any other activator. Moreover, reusability of catalyst, high yields and environmentally benign solvent-free condition are key factors of this protocol.

Background: Generally, it was assumed that Tebbe- and Takai-reagents are useful for methenylation reactions. Objective: Applying these reagents to aromatic ene dicarboxylates, unexpectedly the reduction of double bonds was achieved. There is, however, a different behaviour of both reagents. Takai-reagent yields reduction while Tebbe-reagent prefers isomerisation. Methods: A selective and unique method has been shown to reduce a double bond of ene-dicarboxylates while both carboxylic groups are not affected at all. In addition, this method is easy and very cheap using Takai-reagent. Results: If isomerisation is to be carried out, without any reduction of a double bond, Tebbe-reagent can be applied. To our knowledge, such reactions have not been published yet. Conclusion: We have shown a selective methodology to reduce aromatic ene-dicarboxylates with titanium ylides.

Aim: The current work aims to enhance catalytic performance of gold nanoparticle– carbon nanotube (Au-CNT) composites towards the reduction of p-nitrophenol. Background: The synthesis of Au-CNTs has received extensive attention because of their high stability and catalytic efficiency, particularly as a heterogeneous catalyst in the reduction of pnitrophenol (p-NP) to p-aminophenol (p-AP) However, most of the Au-CNT preparation processes reported in the literatures are time-consuming or require expensive instrumentation. In the present work, Au-CNT catalysts were synthesized via a straightforward, low-cost deposition– precipitation (DP) method. Objective: Evaluate the effect of pH and aging time on catalytic activity of Au-CNTs catalyst. Methods: The Au-CNT nanocomposite catalysts were synthesized using a simple deposition– precipitation method and characterized by Brunauer–Emmett–Teller analysis, fourier transform infrared spectroscopy, atomic absorption spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, and transmission electron microscopy. Results: The particle size and the loading of Au nanoparticles on the CNTs can be easily controlled by varying the pH and aging time during the synthesis process. The nanocomposite catalysts exhibited excellent catalytic activity for the reduction of p-nitrophenol to p-aminophenol in the presence of excess sodium borohydride (NaBH4). The highest rate constant (k) achieved based on the pseudo-first-order kinetic model was 1.2 × 10^-3 s^-1. Conclusion: This study offers a simple and cost-effective route to synthesize Au-CNT catalysts with high stability and catalytic efficiency for large-scale application.

Introduction: Chitin and pectin are important natural polymers which are used as a natural catalyst for the synthesis of tri- and tetra- phenyl substituted 1H-imidazoles. Materials and Methods: The reaction of benzil and aromatic aldehydes with ammonium acetate in the presence of chitin produces 2,4,5-triphenyl-1H-imidazoles and the reaction of benzil, aromatic aldehydes and aniline derivatives with ammonium acetate in the presence of pectin produces 1,2,4,5- tetraphenyl-1H-imidazoles, respectively. Results: The results show that the synthesis of 2,4,5-triphenyl-1H-imidazoles and 1,2,4,5-tetraphenyl- 1H-imidazoles can be catalyzed by chitin and pectin in an effective route, respectively. All synthesized compounds are in good agreement with previously reported compounds. Conclusion: In conclusion, an efficient methodology has been carried out to generate 2,4,5-triphenyl- 1H-imidazoles and 1,2,4,5-tetraphenyl-1H-imidazoles, by using non-toxic, cheap and in available catalysis (chitin and pectin).