Applications of Ionic Liquids in Green Catalysis: A Review of Recent Efforts

: Ionic Liquids (ILs) in their neoteric form have emerged to be a potential ‘green’ alternative of traditional Volatile Organic Compounds (VOCs) as solvents in different fields of industries and academia. Recent investigations on the development of multi-faceted applications of ionic liquids have revealed that they really stand for “environmentally-benign” solvents as far as their impact on the ecology is concerned. This caused them to be an exciting and lucrative subject to explore more and more, and many research groups are involved in the manifestation of their inherent undisclosed legacy. Recently, there has been a huge jump in search of an alternative to conventional metal catalysts in academia as well as in industries due to their pollution-evoking roles. Scientists have explored multiple numbers of homogeneous or heterogeneous mixtures of catalysts incorporating ionic liquids to reduce the extent of contamination in our global environment produced due to catalytic synthesis and chemical transformations. In this review, we have put our concentration on some beneficial and recently explored aspects of the successful implementation of Ionic Liquids in different forms in several fields of catalysis as a ‘green’ alternative catalyst/co-catalyst/solvent for catalysis to replace or minimize the lone and hazardous use of metal and metallic compounds as catalysts as well as chemicals like mineral acids or VOCs as solvents. Here, our study focuses on the inevitable role of ILs in several catalytic reactions like cycloaddition of CO2, electrolytic reduction of CO2, biocatalytic or enzymatic reactions, some of the important organic conversions, and biomass to biofuel conversion as catalysts, cocatalysts, catalyst activator, and solvents.

Magnetic Spinel Ferrite: An Efficient, Reusable Nano Catalyst for HMFSynthesis

Aim: In the present work, the preparation and catalytic activity of spinel ferrite [MFe2O4; M = Fe, Mn, Co, Cu, Ni] nanoparticles to synthesize 5-hydroxymethylfurfural (HMF) have been discussed. Background: Ferrites possess unique physicochemical properties, including excellent magnetic characteristics, high specific surface area, active surface sites, high chemical stability, tunable shape and size, and easy functionalization. These properties make them essential heterogeneous catalysts in many organic reactions. Objective: This study aims to synthesize a series of transition metal ferrite nanoparticles and use them in the dehydration of carbohydrates for 5-hydroxymethylfurfural (HMF) synthesis. Method: The ferrite nanoparticles were prepared via the co-precipitation method, and PXRD confirmed their phase stability. The surface area and the crystallite size of the nanoparticles were calculated using BET and PXRD, respectively. Result: The easily prepared heterogeneous nanocatalyst showed a significant catalytic performance, and among all spinel ferrites, CuFe2O4 revealed maximum catalytic ability. Conclusion: Being a heterogeneous catalyst and magnetic in nature, ferrite nanoparticles were easily recovered by using an external magnet and reused up to several runs without substantial loss in catalytic activity. Others: HMF was synthesized from fructose in a good yield of 71%.

Aqueous Phase Bromination by Micellar Solution of Sodium Dodecyl Sulfate (SDS): An Undergraduate Chemistry Experiment

Background: Bromination is a key reaction in chemical industry, since the organobromines find application in diverse fields like pharmaceuticals, dyes, fire retardants and as intermediates in chemical synthesis. Objective: To carry out green, in-situ bromination of acetanilide in aqueous medium using micellar SDS as catalyst. Methods: Bromination of acetanilide in-situ using potassium bromide as a non-corrosive source of bromine, ceric ammonium nitrate as oxidant, micellar solution of sodium dodecyl sulphate (SDS) as catalyst and water as solvent. Results: p-Bromoacetanilide was prepared in excellent yields, at room temperature, using green chemistry principles. Conclusion: The presented method provides a fast and environmentally safe route for the preparation of p-bromoacetanilide from acetanilide. It avoids the use of volatile, corrosive, and hazardous substances like liquid bromine and acetic acid. The use of water makes it safer and free from hazardous organic solvents. This reaction can be suitably adopted at the undergraduate level and may find use in the synthesis of commercially important bromo compounds.

Iron, Cobalt and Nickel Catalyzed Hydrosilylative Reduction of Functional Groups

: Hydrosilylation is an important transformation in organic synthesis. It has displayed widespread applications in homogenous catalysis and in the commercial production of organosilanes and organosilicon compounds. Though metals like Ru, Rh etc were used widely for achieving hydrosilylation, the increasing environmental concerns and the search for less expensive alternatives resulted in the investigation of transition metals. Metals like Ni, Co etc exhibit potential cost benefits, in addition to their low CO2 foot print and lower toxicity. Thus, transition metal catalysis has emerged as a promising strategy for hydrosilylation. This comprehensive review discusses the catalytic hydrosilylation of various functional groups with non-noble transition metals such as iron, cobalt and nickel in the last decade. Here, the topic is categorized based on the substrate functional groups such as aldehydes, ketones, alkenes, etc.

Kinetics of the Catalytic Combustion of Ethanol and Ethyl Acetate with Estimation of Activation Energy and Rate Constants: An Analytical Study

: 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. 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. Objective: Derive general approximate analytical expressions of ethanol, acetaldehyde, and ethyl acetate molar concentrations inside the particle and reactor phase for various parameter values. Method: 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.

An Efficient Synthesis Of α, β Unsaturated Ketones Via Claisen–Schmidt Condensation Reaction Using Amino Acid Based Ionic Liquids

: Synthesis of chalcone by Claisen–Schmidt condensation using recyclable L- aspartic acid coupled 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 are a flavonoid family and have pharmacological and biological activities. It includes antibacterial, antifungal, immunosuppressive, and anti-nociceptive properties. Objective: Ionic liquid has emerged as a powerful tool for molecular organic solvents and wide liquid range, ease of recovery and reuse, and making them a greener alternative to volatile organic solvents. Thus, our objective was to employ them as dual catalyst and solvent systems to synthesize chalcone via CS condensation in the present work. Method: 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 preceded quickly at room temperature with stirring, the resulting mixture became a biphasic system with the residue at the bottom and the upper phase containing some unreacted substrate separated from the catalyst by filtration and decantation. The catalyst was extracted with CH2Cl2 and split for the next cycle. Results: Claisen–Schmidt condensation accomplished with reasonable to good yields, ranged from 78 to 95% at room temperature in the presence of the [L-AAIL], as compared to the traditional route at more than 100O C. Conclusion: [L-AAIL] are found a highly efficient and eco-friendly catalyst for synthesizing chalcone derivatives at room temperature. [L-AAIL] as a solvent and catalyst will exhibit real advantages by providing a ‘green’ process with the safer operation, 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.

One-pot Synthesis of Novel Thiophene Containing Aminonaphthols using Fe3O4 Nanoparticles as a Recyclable Heterogeneous Catalyst

Background: Metal oxide and metal oxide nanoparticles are gaining significant importance due to their reusability and wide range of catalytic applications in many organic transformations. Objective: To report simple and efficient Fe3O4 catalyzed one-pot five-component reaction protocol to synthesize novel thiophene containing aminonaphthols under solvent-free conditions. Method: To prepare the Fe3O4 nanoparticles by facile and simple co-precipitation method and surface characterization was done using FT-IR, XRD, BET, SEM, and TEM analysis technique. Aminonaphthol derivatives bearing thiophene moiety were synthesized using Fe3O4 nanoparticles under solvent-free conditions. Results: The prepared nanoparticles are smaller in size (15nm) and can be easily detachable. It can be recycled and reused five times without any significant loss of catalytic activity with excellent yields in a short time. The existing protocol for synthesizing amino naphthol becomes feasible and attractive due to the reusability of the 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 to synthesize thiophene containing aminonaphthols. Excellent catalytic activity was perceived in a short reaction time without any co-catalyst or any other activator. Moreover, reusability of catalyst, high yields, and environmentally benign solvent-free condition are vital factors of this protocol.