Roshith Roshan

A novel approach of utilizing quaternized chitosan as a catalyst for the eco-friendly cycloaddition of epoxides with CO2

A novel attempt of using quaternized chitosan (QCHT) as a catalyst for the cycloaddition reaction of allyl glycidyl ether (AGE) and CO2 under solvent-free conditions has been made. The surface quaternization of CHT has been characterized by means of various physicochemical methods, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and elemental analysis. The effects of reaction parameters like catalyst amount, reaction time, reaction temperature, and CO2 pressure have been investigated. The catalyst system was recyclable and was reused. It has been demonstrated that the inherently present hydroxyl group in the catalyst had a synergistic effect with halide anions, and a high yield of cyclic carbonates and excellent selectivity could be obtained under optimum conditions. These results reveal that QCHT is an efficient and environmentally friendly catalyst for the cycloaddition reaction.

Dual-porous metal organic framework for room temperature CO2 fixation via cyclic carbonate synthesis

A novel approach of employing a dual-porous metal organic framework (MOF) in CO2 fixation at room temperature was demonstrated using a micro–mesoporous MOF, UMCM-1-NH2, in the synthesis of various five-membered cyclic carbonates under solventless conditions. Mesopores allow easy guest diffusion and molecular accessibility, while micropores are predominantly helpful in regulating the catalytic interactions in active centres; thus outperforming the properties of pure microporous or pure mesoporous MOFs in cycloaddition. Structural features, acid–base characteristics and physical properties were studied in detail for carrying out a systematic investigation on the cooperative influences of porosity, functionalization and synergism with quaternary ammonium salts in the cycloaddition reaction of CO2 with propylene oxide, so as to arrive at the underlying mechanism. The catalyst was totally recyclable up to five times without compromising the activity and the extent of heterogeneity was also studied. The effects of various reaction parameters like catalyst–cocatalyst ratio, reaction time and reaction temperature have been investigated.

Microwave-assisted synthesis of cyclic carbonates by a formic acid/KI catalytic system

An environment-friendly synthesis of cyclic carbonates from CO2 and epoxides with a HCOOH/KI catalytic system was performed in a microwave reactor. Various epoxide substrates were subjected to microwave irradiated cycloaddition using a HCOOH/KI catalyst. The effects of reaction parameters like catalyst composition, microwave power, CO2 pressure, and reaction time have been investigated. The synergistic influence of the COOH/KI catalyst in the reaction has been compared with that of an OH/KI system and was theoretically simulated using density functional theory.

Aqueous-microwave synthesized carboxyl functional molecular ribbon coordination framework catalyst for the synthesis of cyclic carbonates from epoxides and CO2

A carboxyl-containing coordination polymer catalyst {Cu(Hip)2(Bpy)}n (CHB) was synthesized rapidly in an aqueous medium using microwave energy and characterized for its structure, morphology, acid-base sites and heterogeneity using experimental and physicochemical techniques. The microwave route was established as competent with the hydrothermal pathway. Exploration of the coordination modes of metal–organic framework (MOF) ligands, especially carboxyl spacers, in achieving reactive functional groups is herein illustrated as crucial rather than focusing merely on the porosity of MOF catalysts. The work represents the first report of a carboxyl-containing MOF class material employed for synthesizing cyclic carbonates from epoxide and CO2. The metal–carboxyl mediated cycloaddition of allyl glycidyl ether and CO2 by the cooperative influence of Cu2+ and the COOH of CHB was synergistically enhanced by an ionic liquid co-catalyst to obtain allyl glycidyl carbonate in 89% yield at optimised reaction conditions. The epoxide substrate scope, effect of reaction parameters and catalyst recyclability (up to 5 cycles) were also studied.

Advancements in the Conversion of Carbon Dioxide to Cyclic Carbonates Using Metal Organic Frameworks as Catalysts

Global warming has begun to show its impact on the environment, and it is time to take steps to manage CO2 emissions, so as to regain the balance of carbon cycle. In addition to various capture and sequestration techniques, conversion of CO2 to value added products is high relevant. However, the inertness of CO2 makes catalysts an indispensable part of the process. CO2 undergoes cycloaddition with epoxides to produce cyclic carbonates, which have utility in various applications. Considering the necessity for heterogeneity and activity under ambient conditions, metal organic framework (MOF) catalysts have recently emerged as prospective candidates for cyclic carbonate synthesis. These porous hybrid inorganic–organic crystals are also excellent materials for gas storage and separation, including CO2 gas. Thus, MOFs could efficiently capture CO2 and catalytically convert them to cyclic carbonates. In this review, we discuss the recent advancements in the design of MOF catalysts for cyclic carbonate synthesis.

Ionic liquid tethered post functionalized ZIF-90 framework for the cycloaddition of propylene oxide and CO2

A novel heterogeneous one-component catalyst was developed by the covalent post functionalization of zeolitic imidazolate framework-90 (ZIF-90) with a pyridinium based ionic liquid (IL) to generate IL supported ZIF-90 (IL-ZIF-90). The synthesized catalyst has been characterized using a range of analytical, spectroscopic, and electron microscopy techniques followed by successful employment for the solventless cycloaddition of epoxides and CO2 to yield cyclic carbonates under mild reaction conditions. The effects of reaction parameters like catalyst amount, reaction time, reaction temperature, and CO2 pressure have been investigated. A reaction mechanism for the IL-ZIF-90 catalyzed PO–CO2 cycloaddition has been proposed on the basis of density functional theory (DFT) calculations. The catalyst system was separable by centrifugation and reused four consecutive times successfully. In general, it can be suggested that IL supported porous metal organic frameworks (MOFs) may introduce a new class of highly porous catalyst species showing excellent CO2 transforming capability.

Catalytic applications of immobilized ionic liquids for synthesis of cyclic carbonates from carbon dioxide and epoxides

The catalytic applicability of ionic liquids immobilized on various support materials such as silica, polystyrene and biopolymers in the cycloaddition of carbon dioxide with epoxides is reviewed in this work. Comparisons of the catalytic efficiency of these various catalysts have been done from the aspect of turnover number and reusability. The studies revealed that ionic liquids or support materials possessing hydrogen bonding capable groups exhibited enhanced catalytic activity towards cyclic carbonate synthesis. Moreover, the increased quest towards environmentally benign materials has renewed the search for biocompatible materials as support for ionic liquids.

Pillared Cobalt–Amino Acid Framework Catalysis for Styrene Carbonate Synthesis from CO2 and Epoxide by Metal–Sulfonate–Halide Synergism

The sulfonate anion is proposed as a remarkable partaker in catalyzing epoxide–CO2 cycloaddition for cyclic carbonate synthesis. The role is illustrated by the concerted action of a sulfonate‐rich cobalt–amino acid framework catalyst [{Co(4,4′‐bipy)(L‐cys)(H2O)}⋅H2O]n (2 D‐CCB) and a quaternary ammonium bromide co‐catalyst in synthesizing styrene carbonate (SC) at a turnover number of 228. SC yield at atmospheric pressure is presumed to result from the activation of CO2 by the sulfonate group. The involvement of SO3− anions as basic sites in 2 D‐CCB is ascertained from the initial rate (r0) for catalyzing Knoevenagel condensation reactions and by using CO2 temperature programmed desorption. Microwave pulses are used for synthesizing 2 D‐CCB at a rate that is 288‐fold faster than conventionally employed solvothermal methods. Unambiguous evidence for the pulsating role‐play of sulfonate groups in 2 D‐CCB is perceived by comparing the activity of an analogous metal organic framework (3 D‐CCB) in which the sulfonate oxyanions are jammed by coordination with cobalt. 2 D‐CCB is analyzed for heterogeneity, and reused four times.

An lcy-topology amino acid MOF as eco-friendly catalyst for cyclic carbonate synthesis from CO2: Structure-DFT corroborated study

The concept of bio-metal-organic framework (bio-MOF) catalysts for CO2 transformation was devised using L-glutamic acid as the natural surrogate for synthetic ligands, and demonstrated their catalytic efficacy for the first time, in the cycloaddition of CO2 with epoxides, supplemented with the structure–DFT correlation. The water stable amino acid bio-MOF, zinc-glutamate-MOF (ZnGlu), with a rare 3D topology (33·59·63)-lcy was synthesized as single crystals and bulk, through an ecofriendly protocol in aqueous medium, from zinc and the proteinogenic amino acid, L-glutamic acid. Amino acid MOFs (AA-MOFs), owing to their economic and environmental factors, are expected to be the future of MOF chemistry at industrial levels. The ZnGlu catalyst with open metal sites was successfully demonstrated as the first bio-MOF catalyst for cyclic carbonate synthesis from CO2 and epoxides, and its efficiency was compared with those of prominent synthetic MOFs reported so far in the process. The as-synthesized catalyst operated even under moist conditions, was thermally and chemically stable; heterogeneous, easily separable (due to its high selectivity, absence of synthesis solvents, and easy catalyst recovery by filtration) and was recycled up to four times. Mechanistic aspects, possible intermediates, transition states and pathways were portrayed using a combination of the experimental inferences, previous reports and ab initio quantum mechanical calculations (DFT techniques) by its correlation with the single crystal XRD structure and topology.

Organic sulphonate salts tethered to mesoporous silicas as catalysts for CO2 fixation into cyclic carbonates

A series of mesoporous silica materials tethered with the sulphonate salts of organic bases were synthesized and their catalytic activity for CO2–epoxide cycloaddition was investigated. The sulphonate group was supported on silica through the functionalization and subsequent oxidation of 3-mercaptopropyltrimethoxysilane (3-MPS) by a post-grafting method. All the synthesized materials have been characterized using various physicochemical techniques such as SAXS, BET, SEM, TEM, FTIR and XPS. The as-formed SBA-15(SO3H) was neutralized with different organic bases such as 4-dimethylaminopyridine, triethanolamine and triethylamine, such that the SO3H group ionizes to become the SO3− ion. These materials along with KI displayed promising CO2 conversion yields with excellent selectivity towards the desired product, cyclic carbonates, with a turnover frequency (TOF) as high as 1900 h−1. The catalysts were thermally stable and their reusability studies were also performed. The synergistic play between SO3− and KI is supposed to be the reason behind the good catalytic rates exhibited by this catalytic system. All the parameter studies have also been carried out.