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The ruthenium catalysed cross-metathesis of terpenoids with methyl acrylate and methyl methacrylate was used to prepare new terpenoids and to improve, to a large extent, the synthesis of known terpenoids. In particular, the cross-metathesis of mono-unsaturated terpenoids was very efficient whereas the transformation of terpenoids incorporating two double bonds was more difficult due to side reactions. The cross-metathesis reactions were carried out under environmentally friendly conditions either in dimethyl carbonate or under solvent-free conditions. [ABSTRACT FROM AUTHOR]

A general visible-light-induced catalyst-/additive-free strategy was developed for the construction of various aroylated heterocycles (55 examples, up to 95% yield, including modification of pharmaceuticals and natural products) such as thioflavones, benzimidazo[2,1-a]isoquinolin-6(5H)-ones, indolo[2,1-a]isoquinolin-6(5H)ones, quaternary 3,3-dialkyl 2-oxindoles, quinoxalin-2(1H)-ones, and benzo[e][1,2,3]oxathiazine 2,2-dioxides in a green solvent (dimethyl carbonate) under air and room temperature conditions. This practical acylation process was achieved using 4-acyl-1,4-dihydropyridines (acyl-DHPs) as acylating reagents under mild conditions, avoiding the use of catalysts, bases, additional oxidants, and traditional organic solvents. [ABSTRACT FROM AUTHOR]

Homogeneous molecular catalysts are valued for their reaction specificity but face challenges in manufacturing scale-up due to complexities in final product separation, catalyst recovery, and instability in the presence of water. Heterogenizing these molecular catalysts, by attachment to a solid support, could transform the practical utility of molecular catalysts, simplify catalyst separation and recovery, and prevent catalyst decomposition by impeding bimolecular catalyst interactions. Previous strategies to heterogenize molecular catalysts via ligand-first binding to supports have suffered from reduced catalytic activity and leaching (loss) of catalyst, especially in environmentally friendly solvents like water. Herein, we describe an approach in which molecular catalysts are first attached to a metal oxide support through acidic ligands and then "encapsulated" with a metal oxide layer via atomic layer deposition (ALD) to prevent molecular detachment from the surface. For this initial report, which is based upon the well-studied Suzuki carbon–carbon cross-coupling reaction, we demonstrate the ability to achieve catalytic performance using a non-noble metal molecular catalyst in high aqueous content solvents. The catalyst chosen exhibits limited catalytic reactivity under homogeneous conditions due to extremely short catalyst lifetimes, but when heterogenized and immobilized with an optimal ALD layer thickness product yields >90% can be obtained in primarily aqueous solutions. Catalyst characterization before and after ALD application and catalytic reaction is achieved with infrared, electron paramagnetic resonance, and X-ray spectroscopies. [ABSTRACT FROM AUTHOR]

The present report focuses on the solvent effect on furfural production from xylose in biphasic systems with methods including combined experiments, molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Six most effective and commonly used biphasic solvents for furfural production were comparatively analyzed and discussed based on the kinetic study, partition coefficient, degradation behavior of furfural in organic solvents, distribution of solvent molecules around xylose/furfural molecules, hydrogen bonding, moving trajectories of xylose/furfural, and the solvation free energy. During the hydrothermal reaction of xylose to furfural in biphasic systems, it was found that the conversion efficiency of biphasic systems can be ordered as DCM/H2O > 2-MTHF/H2O > 2-butanol/H2O ≈ MIBK/H2O > CPME/H2O > toluene/H2O according to the xylose conversion and furfural yield, which are dominated by the solvation free energy (ΔGsol) of furfural in organic solvents, and also be affected by three other factors, namely, the maximum solubility of furfural in organic solvents, the ΔGsol value of organic solvents in water, and the side reaction of furfural in organic solvents. The degradation rate of furfural in 2-butanol was detected to be the fastest, and molecular dynamics simulation data showed that the hydrogen bonding between furfural and 2-butanol may accelerate the degradation of furfural. DCM has excellent extraction ability for furfural, and the maximum furfural yield in the DCM/H2O system (81.64%) is much higher than that in other systems during the hydrothermal reaction without additional catalysts. [ABSTRACT FROM AUTHOR]

RuNi nanoparticles (NP) were prepared by decomposition of [Ru(η4-C8H12)(η6-C8H10)] and [Ni(η4-C8H12)2] by H2 in the presence of polyvinylpyrrolidone (PVP) at 85 °C using several Ru/Ni ratios. The nanoparticles display a segregated structure in which Ni is on the surface, as ascertained by wide angle X-ray scattering (WAXS). The catalytic activity in the selective hydrogenation of furfural of these RuNi NP was correlated with the Ru content. High selectivity towards the partially hydrogenated product 2-(hydroxymethyl)furan (HF) was found when carrying out the reaction in tetrahydrofuran (THF). A different scenario was found when using a protic polar solvent, 1-propanol. Catalysts displaying Ru on the surface were able to hydrogenate the heteroaromatic ring, while those with Ni on the surface were highly selective towards the partially hydrogenated product. In addition, Ru surfaces were prone to catalyse the acetalization reaction in the presence of the alcoholic solvent, while the addition of Ni supressed this reactivity. Density functional theory (DFT) calculations performed on hydrogenated Ru nanoparticles (Ru55H70) show differences in the adsorption energies of several reagents, products, reaction intermediates, and solvents onto the Ru NP surface, which are in line with the experimental catalytic results. [ABSTRACT FROM AUTHOR]

A one-pot procedure for the synthesis of biologically relevant coumarin hydrazones using a three-component reaction between 4-hydrocoumarins, primary aromatic amines and tert-butyl nitrite under ball-milling in the absence of any catalysts/additives and solvents has been developed. The mechanical force implements the Csp2–H functionalization of 4-hydroxycoumarins via C-3 dehydrogenative aza-coupling with ease. The product was isolated by simple washing of the crude reaction residue with aqueous ethanol, followed by simple filtration. No chromatographic purification was required. Catalyst- and solvent-free reaction conditions, use of ball-milling as a green tool, lack of a need for chromatographic purification, broad substrate scope and tolerance for various functional groups, high yields of products at short reaction times (no more than 6 min), a clean reaction profile, and gram-scale synthetic applicability make this procedure green and cost-effective. [ABSTRACT FROM AUTHOR]

With green ethanol as the sole solvent, various 3-aminomethylated imidazoheterocycles were efficiently synthesized in one step through a four-component reaction of equimolar cheap and commercially available reactants at ambient temperature under metal-free, oxidant-free and mild conditions. [ABSTRACT FROM AUTHOR]

Ionic liquids are of great interest as potential solvents/catalysts for the production of fuels and chemicals from lignocellulosic biomass. Attention has focused particularly on the pretreatment of lignocellulose to make the cellulose more accessible to enzymatic hydrolysis. Any biomass processing requires a reduction in the size of the harvested biomass by chipping and/or grinding to make it more amenable to chemical and biological treatments. This paper demonstrates that significant energy savings can be achieved in the grinding of pine wood chips when the ionic liquid is added before the grinding operation. We show that this is due to the lubricating properties of the ionic liquids and not to physico-chemical modifications of the biomass. A brief impregnation of the chipped biomass results in higher savings than a longer treatment. [ABSTRACT FROM AUTHOR]

Inexpensive bulk Ni–Sn alloy-based catalysts demonstrated a unique catalytic property in the selective conversion of C5-furan compounds (e.g., furfuraldehyde (FFald), furfuryl alcohol (FFalc), and 2-methylfuran (2-MTF)) in an ethanol/H2O solvent mixture and selectively produced 1,4-pentanediol (1,4-PeD) in a one-pot reaction. The synergistic actions between the bulk Ni–Sn alloy catalyst, hydrogen gas, and the hydroxylated H2O or ethanol/H2O solvents are believed to play a prominent role in the catalytic reactions. Bulk Ni–Sn alloy catalysts that consisted of Ni3Sn or Ni3Sn2 alloy phases allowed an outstanding yield of 1,4-PeD up to 92% (from FFald), 67% (from FFalc), and 48% (from 2-MTF) in ethanol/H2O (1.5 : 2.0 volume ratio) at 433 K, 3.0 MPa H2 and 12 h. As the reaction temperature increased to 453 K, the yield of 1,4-PeD slightly decreased to 87% (from FFald), whereas it slightly increased to 71% (from FFalc). The bulk Ni–Sn alloy catalysts were reusable without any significant loss of selectivity. [ABSTRACT FROM AUTHOR]

Exploitation of hydrogen as an energy carrier requires the development of systems for its storage and delivery. Formic acid has been proposed as valuable hydrogen carrier compound, due to its relatively high hydrogen content (53 g L−1), the latter being easily and cleanly released in catalytic reactions under mild conditions (HCOOH → H2 + CO2). Ionic liquids are interesting solvents for homogeneous catalyzed formic acid decomposition systems as their extremely low volatility avoids solvent contamination of the produced hydrogen stream. In this paper an outstandingly simple, robust and active catalyst system is presented, namely RuCl3 dissolved in 1-ethyl-2,3-dimethylimidazolium acetate (RuCl3/[EMMIM][OAc]). This system proved to be fully recyclable over 10 times. Turnover frequencies (TOF) of 150 h−1 and 850 h−1 were obtained at 80 °C and 120 °C, respectively. [ABSTRACT FROM AUTHOR]

An efficient method for dispersing active metal colloidal nanoparticles onto supports uniformly is revealed in this paper. The critical feature of this method is to separate the stabilizer simply with the phase-switch function of scCO2; with it the highly dispersed Pd colloidal catalysts were prepared, and the forming procedure is analyzed and discussed in detail. The present work not only overcame the common difficulties of removing the stabilizers in the preparation of supported colloidal particles, but also provided a facile and green process for preparing supported metal colloidal nanoparticles with using the environmentally benign solvent of scCO2. [ABSTRACT FROM AUTHOR]

Among the deep eutectic solvents (DES), natural deep eutectic solvents (NADES) formed by d-glucose and racemic malic acid are suitable media to perform the enantioselective l-proline catalyzed intermolecular aldol reaction, creating simultaneously and selectively a C–C bond and a new stereocenter. The scope of the reaction was found to be broad, with products being obtained with good levels of diastereo- and enantioselectivities. Furthermore, when the reaction was performed at a large scale, the catalyst together with the reaction media can be recovered by simple water extraction and reused at least three times affording similar results. Therefore, the use of NADES as reaction media to carry out a VOC-free selective process has been demonstrated for the first time. The process is clean, cheap, simple and scalable and meets most of the criteria to be considered as a sustainable and bio-renewable process, with the reaction media and catalyst arising directly from Nature. [ABSTRACT FROM AUTHOR]

β-cyclodextrin-butane sulfonic acid is reported to be an efficient catalyst for the one-pot synthesis of 1-amidoalkyl-2-naphthols by the multicomponent condensation of aromatic aldehydes, β-naphthol and amides under solvent-free conditions. The present methodology offers several advantages such as shorter reaction time, mild reaction conditions, a simple operational procedure and use of a recyclable catalyst. [ABSTRACT FROM AUTHOR]

Palladium catalysed cross-couplings reactions have been a dominant method in synthetic chemistry for decades. Despite this, the role of the solvent is often taken for granted and poorly understood. Regulations affecting some the most frequently used solvents for cross-coupling reactions are accelerating current trends towards using new types of solvents. In this review, the fundamental interactions between solvent and catalyst are explained so that it may inform the rational selection of high performance and safe solvents. The popular cross-coupling methodologies are addressed (Suzuki, Stille, Kumada, Negishi, Hiyama, Heck, Sonogashira, and Buchwald–Hartwig reactions) and novel solvents introduced. [ABSTRACT FROM AUTHOR]

An economically viable and environmentally benign continuous flow intensified process has been developed that demonstrates its ability to upgrade biomass into potential biofuels, solvents, and pharmaceutical feedstocks using a bimetallic AgPd@g-C3N4 catalyst. [ABSTRACT FROM AUTHOR]

A convenient catalyst-free, three-component procedure was developed for the synthesis of tetrasubstituted pyrroles under solvent-free conditions and in green solvents glycerol, PEG-200 and water. A sequential enamine-formation, Michael addition and intramolecular cyclization of primary amines, 1,3-dicarbonyl compounds and isatin-derived Michael acceptors afforded 3-(1H-pyrrol-3-yl)indolin-2-ones in excellent yields. In this simple one-pot transformation the requirement of column chromatography purification of the products was completely avoided. Besides, the method is highly environmentally benign and atom-economical, and the only side product of this reaction was two molecules of water. A comparative study for the four developed conditions showed that the solvent-free conditions were superior regardless of the nature of the starting materials, and the green solvents were effective for alkyl and benzylamines affording higher yields compared to arylamines. The preliminary in vitro cytotoxic studies of a representative compound against Ehrlich's ascites carcinoma (EAC) tumor cells showed significant activity with a CTC50 value of 15.64 μM. [ABSTRACT FROM AUTHOR]

The oxidative N-demethylation of tropane alkaloids to their nortropane derivatives has been investigated using H2O2 and an iron(iii) tetraamido macrocycle (FeIII-TAML) catalyst. The yields of the nortropanes were found to be dependent on the amount of H2O2 used in the reaction, the catalyst loading, the nature of the organic co-solvent and the type of tropine substrate. N-Hydroxy-nortropane, N-formyl-nortropane and tropane-N-oxide derivatives were identified as by-products of the reaction. After screening various reaction conditions, the optimised conditions were applied to the N-demethylation of atropine and scopolamine at preparative scales and the desired products, noratropine and norscopolamine, obtained following one pot reactions in good yields and high purity without the need for any chromatographic purification steps. [ABSTRACT FROM AUTHOR]

Selective oxidation of sulfides was successfully performed by employing oxone (2KHSO5·KHSO4·K2SO4) as oxidant without utilization of any catalyst/additive under mild reaction conditions. Notably, the reaction can be controlled by the chosen solvent. When ethanol was used as the solvent, sulfoxides were obtained in excellent yield; the reaction almost exclusively gave the sulfone in water. Furthermore, this protocol worked well for various sulfides to the corresponding sulfoxides in ethanol or sulfones in water. [ABSTRACT FROM AUTHOR]

The direct synthesis of hydrogen peroxide from molecular H2 and O2 represents a green and economic alternative to the current anthraquinone process used for the industrial production of H2O2. In order for the direct process to compete with the anthraquinone process, there is a need for enhanced H2O2 yields and H2 selectivity in the process. We show that Au–Pd-exchanged and supported Cs-containing heteropolyacid catalysts with the Keggin structure are considerably more effective in achieving high H2O2 yields in the absence of acid or halide additives than previously reported catalysts. The Au–Pd-exchanged Cs-heteropolyacid catalysts also show superior H2O2 synthesis activity under challenging conditions (ambient temperature, water-only solvent and CO2-free reaction gas). Au plays a crucial role in achieving the improved performance of these heteropolyacid-based catalysts. The heteropolyacid limits the subsequential hydrogenation/decomposition of H2O2. [ABSTRACT FROM AUTHOR]

The surface hydrophobization through heterogeneous chemical modification of bacterial (and vegetable) cellulose fibers with several anhydrides (acetic, butyric, hexanoic and alkenyl succinic anhydrides) and hexanoyl chloride suspended in an ionic liquid, tetradecyltrihexylphosphonium bis(trifluoromethylsulfonyl)imide, [TDTHP][NTf2], was studied. Furthermore, in the reaction with hexanoyl chloride, another ionic liquid, N-hexyl-4-(dimethylamino)pyridinium bis(trifluoromethylsulfonyl)imide, [C6N(CH3)2py][NTf2], was used instead of common organic bases as catalyst and to trap the released HCl. The analysis of the ensuing modified fibers by FTIR, XRD and SEM clearly showed that the esterification reactions occurred essentially at the fibers' outmost layers, not affecting their ultrastructure. The degree of substitution (DS) of the ensuing esterified fibers ranged from less than 0.002 to 0.41; and in all instances, the fibers' surface acquired a high hydrophobicity. This novel approach constitutes an important strategy in the preparation of modified fibers under greener conditions relaying in the use of non-volatile solvents. [ABSTRACT FROM AUTHOR]

Highly concentrated melt systems consisting of choline chloride (ChCl) and up to 50 wt% of carbohydrates, corresponding to carbohydrate concentrations of 2.9 to 3.1 mol/L, have been used for the conversion of the carbohydrate content into 5-hydroxymethylfurfural (HMF) in the presence of catalysts. Apart from the monosaccharides d-fructose and d-glucose, the disaccharide sucrose and the polyfructan inulin were successfully converted into HMF. The reported conditions with short reaction times at high concentrations may allow for high space-time yields, which may be of interest for the development of efficient continuous processes for the conversion of carbohydrates into HMF. In a preliminary ecological evaluation, the ChCl/d-fructose system is compared to other representative solvents for the synthesis of 5-hydroxymethylfurfural. The melts have an inherent low toxicological impact due to their negligible vapour pressure. [ABSTRACT FROM AUTHOR]

Simple ammonium ionic liquids are efficient catalysts in promoting Saucy–Marbet reactions of unsaturated alcohols with unsaturated ethers to afford the corresponding unsaturated ketones, eliminating the need for volatile organic solvents. The effect of the anions and the cations of ionic liquids, quantity of ionic liquid, temperature, and chain-length of unsaturated alcohols on the reaction was investigated. The results showed that the Saucy–Marbet reaction was heavily influenced by the acidity of ionic liquid and [Et3NH][HSO4] had the best catalytic activity. The conversion and selectivity obtained with this method are significantly increased in comparison to those catalyzed by traditional acid. Furthermore, the ionic liquid could be easily separated and reused with a slight loss of its activity. It provided a good alternative way for the industrial synthesis of unsaturated ketones. [ABSTRACT FROM AUTHOR]

At 35 °C, in the presence of supercritical carbon dioxide (80–150 bar) as a solvent, α-olefins (RCHCH2, R = C4–C6) undergo highly selective self-metathesis catalyzed by supported Re-oxide (7%). To the best of our knowledge, this is the first procedure for the metathesis of alkenes, in which heterogeneous catalysts are combined with the use of dense CO2. The intrinsic eco-compatibility and the unique physicochemical properties of this medium offer both environmental and synthetic advantages: not only conventional toxic solvents (e.g. n-heptane and toluene) can be replaced, but the reaction is faster. For instance, after 2 h, the average conversion of 1-octene is 67% and 40% in scCO2and n-heptane, respectively. The product of self-methatesis, 7-tetradecene, can be isolated in yields up to 68%. At 90 bar, the reaction is rather sensitive to the mole fraction of the olefin (in scCO2); though, the enhancement of the pressure (and the density) of the supercritical medium does not induce significant effects on either the rate or the selectivity of the process. The nature of the catalytic support also greatly affects the reaction outcome: Re-oxide shows good activity if dispersed over γ-Al2O3, while silica-based systems are ineffective. [ABSTRACT FROM AUTHOR]

Catalytic performance of different supported heteropoly acids (HPAs) in the synthesis of β-enaminones and β-enamino esters from various substituted amines and β-diketones or β-keto esters has been studied. In order to improve the yield and reaction time, the effect of various solvents, HPA loading, different amount of the catalyst and solventless conditions have been investigated. 40% (w/w) PW/SiO2 was found to be a very efficient and reusable catalyst in comparison with others, under solvent free conditions. In this eco-friendly approach, the usage of organic solvents and hazardous reagents were minimized. Also, a high yield of products within short reaction times were obtained. [ABSTRACT FROM AUTHOR]

The water soluble Pd complex of dicyclohexyl(2-sulfo-9-(3-(4-sulfophenyl)propyl)-9H-fluoren-9-yl)phosphine was used for an efficient copper free and sustainable reaction protocol for Sonogashira cross couplings. Using a water/ipropanol mixture as the solvent and K2CO3 as base, numerous heterocyclic and aryl bromides and chlorides were reacted with various acetylenes in near quantitative yield at 1 mol% catalyst loading and 90 °C. [ABSTRACT FROM AUTHOR]

Under solvent-free conditions, (E)-2-aryl-1-cyano-1-nitroethenes 1a–l rapidly react with 1-(trimethylsilyloxy)-cyclohex-1-ene (2a) with a complete regio- and diasteroselectivity and leading to the exclusive formation of the cis-fused hexahydro-4H-benzoxazine-2-oxides 3a–l, which were isolated without the need for a work-up procedure in excellent yields. [ABSTRACT FROM AUTHOR]