1,720,995 research outputs found
Preparation of CO2/diene copolymers: Advancing carbon dioxide based materials
No full textCO2-based materials: Metastable CO2/diene-based lactones, which were prepared by the palladium-catalyzed telomerization of CO2 and dienes, easily undergo aerobic radical homo-polymerization to give novel CO2-rich polymers. This two-step reaction set-up expands the potential applications of CO2-based copolymers by adding innovative compositions, structures, and properties
Recent advances in the catalytic preparation of cyclic organic carbonates
No full textThe catalytic formation of cyclic organic carbonates (COCs) using carbon dioxide (CO2) as a renewable carbon feed stock is a highly vibrant area of research with an increasing amount of researchers focusing on this thematic investigation. These organic carbonates are highly useful building blocks and nontoxic reagents and are most commonly derived from CO2 coupling reactions with oxirane and dialcohol precursors using homogeneous catalysis methodologies. The activation of suitable reaction partners using catalysis as a key technology is a requisite for efficient CO2 conversion as its high kinetic stability poses a barrier to access functional organic molecules with added value in both academic and industrial laboratories. Although this area of science has been flourishing for at least a decade, in the past 2-3 years, significant advancements have been made to address the general reactivity and selectivity issues that are associated with the formation of COCs. Here, we present a concise overview of these activities with a primary focus to highlight the most important progress made and the opportunities that catalysis can bring about when the synthesis of these intermediates is optimized to a higher level of sophistication. The attention will be limited to those cases in which homogeneous metal-containing systems have been employed because they possess the highest potential for directed organic synthesis using CO2 as molecular building block. This review discusses examples of exceptional reactivity and selectivity, taking into account the challenging nature of the substrates that were involved, and mechanistic understanding guiding the optimization of these protocols is also highlighted. (Chemical Equation Presented)
Sustainable Valorisation of Renewables through Dialkyl Carbonates and Isopropenyl Esters
Full text linkThis review showcases a thorough analysis of reactions and applications of the most widespread linear and alkylene organic carbonates (DACs) as dimethyl-, diethyl-, ethylene-, and propylene- carbonates (DMC, DEC, EC, and PC, respectively), and a representative enol ester as isopropenyl acetate (iPAc), for the chemical functionalisation and upgrading of renewable compounds, both bio-based platform molecules and biopolymers. The work which follows a previous survey published by us in 2018 and limited to DMC only, is organised into five sections where the literature screening encompasses the past 4 years in the case of DMC and a wider timespan of five-six years for other homologues/analogues carbonates and iPAc. After a general introductory section on benign-by-design processes for the conversion of biomass derivatives, a description of synthetic methods of DACs follows. Most of the review content is then focused on reactions in which DACs and iPAc act as alkylating, carboxylating, and acylating agents, respectively, and processes where the same compounds are used as solvents. Topics are grouped starting from the valorisation of small renewable molecules as glycerol, cyclic carbonates, carbonyl derivatives of furfural and HMF, then proceeding with bio-monomers, and ending up with the synthesis and functionalisation of biopolymers. The investigated examples have been detailed by providing conditions and scope, the proposed reaction mechanisms when available, and a rationale behind the choice of reaction/process parameters (T, p, catalyst(s), etc.). Criticism and comments have been put forward on the pros and cons of the described methods and their perspectives, as well as on those studies which still require follow-ups and more in-depth analyses
Sustainable conversion of carbon dioxide: The advent of organocatalysis
No full textThe conversion of carbon dioxide (CO<inf>2</inf>), an abundant renewable carbon reagent, into chemicals of academic and industrial interest is of imminent importance to create a higher degree of sustainability in chemical processing and production. Recent progress in this field is characterised by a plethora of organic molecules able to mediate the conversion of suitable substrates in the presence of CO<inf>2</inf> into a variety of value-added commodities with advantageous features combining cost-effectiveness, metal-free transformations and general substrate activation profiles. In this review, the latest developments in the field of CO<inf>2</inf> catalysis are discussed with a focus on organo-mediated conversions and their increasing importance in serving as practicable alternatives for metal-based processes. Also a critical assessment of the state-of-the-art methods is presented with attention to those features that need further development to increase the usefulness of organocatalysis in the production of organic molecules of potential commercial interest
Greener and Sustainable Applications of Phosphorous and Sulfur Ylides
Full text linkThe present review highlights relevant recent examples (2013-2018) of sustainable synthetic reactions involving phosphorus and sulfur ylides. These examples include catalytic, halide- and base-free Wittig olefination reactions and P-ylides as CO2 activators. They also include sustainable protocols for the synthesis of S-ylides and recent applications of these C1 synthons as carbene precursors and in selected rearrangement reactions
fixation into epoxides
Full text linkHerein we describe the syntheses of a series of molybdate and polyoxomolybdate ionic liquids (ILs), their full spectroscopic characterisation (FT-IR, H-1-, C-13-, P-31-, and Mo-95-NMR and ICP-MS), a comparison of their properties, and their applications as bifunctional catalysts for CO2 insertion into epoxides. The synthetic procedures to obtain ILs rely on anion exchange and acid-base reactions, including an innovative route for the synthesis of molybdate ionic liquids (Mo-ILs) using a halide-free organic IL precursor. The use of Mo-ILs as catalysts for CO2 fixation was investigated using 1,2-epoxyhexane as a model substrate. In the presence of 2.5 mol% of tetrabutylammonium molybdate, hexane carbonate was obtained in up to 86% yield at T = 120 degrees C, p(0)(CO2) = 30 bar in t = 9 h, under solventless conditions and without any added halide co-catalysts. The substrate scope was broadened to other 12 terminal and internal epoxides; moreover, the reaction was scaled up to 2 g of the substrate and catalyst recyclability was demonstrated up to 5 recycles
Highly Efficient Organocatalyzed Conversion of Oxiranes and CO2 into Organic Carbonates
No full textA binary catalyst system based on tannic acid/NBu4X (X=Br, I) is presented as a highly efficient organocatalyst at very low catalyst loading for the coupling of carbon dioxide and functional oxiranes to afford organic carbonates in good yields. The presence of multiple polyphenol fragments within the tannic acid structure is considered to be beneficial for synergistic effects that lead to higher stabilization of the catalyst structure during catalysis. The observed turnover frequencies (TOFs) exceed 200 h-1 and are among the highest reported to date for organocatalysts in this area of CO2 conversion. This organocatalyst system presents a useful, readily available, inexpensive, and, above all, reactive alternative for most of the metal-based catalyst systems reported to date
2‐formyl‐5‐(hydroxymethyl)furan (HMF) derivatives as active complexing agent for CO2 insertion reaction
Full text linkRenewable-based furan compounds derived from 2-formyl-5-(hydroxymethyl)furan (5-HMF) were successfully employed as catalysts to synthesize cyclic organic carbonates through the reaction of carbon dioxide with epoxides. The effects of temperature, reaction time, reagent ratios, and carbon dioxide pressure were optimized before evaluating various bio-based complexing agents in combination with different alkali metal halide salts. Among them, 2,5-bis(hydroxymethyl)tetrahydrofuran (BHTHF) showed the highest efficiency as a complexing agent when paired with sodium bromide (NaBr), enabling the production of industrially relevant cyclic carbonates in high yields (12 examples, achieving 94-99% epoxide conversion and 70-99% carbonate selectivity) under mild pressure conditions (carbon dioxide pressure of 1-10 bar, reaction time of 6 hours, and temperature of 120 °C). Additionally, the BHTHF/NaBr catalytic system demonstrated high stability, maintaining its performance over nine consecutive epoxide additions (8 mmol each) without any loss of efficiency
Preparation of polymeric membranes and microcapsules using an ionic liquid as morphology control additive
No full textHydrophilic porous polyethersulfone (PES) membranes and microcapsules were prepared via Non-Solvent Induced Phase Separation (NIPS) with the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) as structure control agent, added to the conventionally employed PVPK17 pore former. The introduction of [BMIM][PF6] affects the phase inversion mechanism, resulting in different morphologies of the materials. Optimal conditions for the preparation of membranes (ILMs) were: 10-15 wt.% PES, 0-4 wt.% PVPK17, 5-25 wt.% [BMIM][PF6], while slightly different conditions were applied for the preparation of microcapsules (ILMCs): 10% wt.% PES, 0-4% wt.% PVPK17, and 5-15 wt.% [BMIM][PF6]. Thus, the produced porous spongy microcapsules (average diameter â\u88¼800 μm) and flat sheet ionic liquid membranes (ILMs) were characterized by electronic microscopy (SEM), FTIR and Raman spectroscopy and thermal analysis. [BMIM][PF6] concentration is a key factor for controlling the internal membrane morphology. Indeed, higher concentrations of [BMIM][PF6] additive increases the viscosity of casting solution and reduces solvent exchange speed, thereby altering the membrane morphology from a channelled structures (finger-like) to a spongy type
Acid-Catalyzed Reactions of Isopropenyl Esters and Renewable Diols: A 100% Carbon Efficient Transesterification/Acetalization Tandem Sequence, from Batch to Continuous Flow
No full textA new acid-catalyzed tandem sequence was investigated for the upgrading of renewable 1,2-diols such as propylene glycol (PG) and ethylene glycol (EG), with isopropenyl esters. For example, at 50 °C and in the presence of Amberlyst-15, the reaction of PG with nontoxic isopropenyl acetate allowed an initial irreversible monotransesterification of the diol, releasing acetone which then promoted acetalization on a second molecule of the glycol. The overall protocol was 100% carbon efficient, affording water as the sole byproduct. The reaction scope was extended to higher homologues of enol esters as isopropenyl-octanoate and phenylbutyrate. Additionally, the tandem sequence was successfully transferred in the continuous-flow (CF) mode where the catalyst (Amberlyst-15) could be used virtually indefinitely without loss of performance, and the solvent (THF or CPME) was quantitatively recovered and reused. Under CF conditions, the reaction of PG with isopropenyl acetate could be run at 30 °C and atmospheric pressure with a (nonoptimized) productivity up to 9.7 mmol gcat-1 h-1, 3 times higher than that achieved in the batch mode. When ethylene glycol was used, a lower tandem selectivity was observed due to predominance of transesterification products, mono- and diesters, over the acetal compound
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