External Catalyst Research Articles

Highly aligned growth of carbon nanotube forests with in-situ catalyst generation: A route to multifunctional basalt fibres

Hierarchical fabrics are gaining ever-growing practical interest, thanks to the possibility of combining different properties into a single textile, particularly useful for applications such as high-performance composites showing in situ structural health monitoring capabilities. In this study, homogeneously aligned carbon nanotube forests are directly grown on basalt fabrics by a fast (∼15 min) chemical vapour deposition process without any external catalyst addition providing, for the first time, a highly dense coverage of the underlying substrate. It is demonstrated by transmission electron microscopy that the direct growth of nanotubes on basalt fibres is catalysed by the microstructural segregation of ferrous iron and its subsequent reduction in hydrogen atmosphere to nanocrystalline metallic iron. It is shown that in situ growth requires a pre-treatment etching which can be conducted in mild basic or acidic conditions, achieving optimum performance with an alkaline attack, without compromising the tensile strength of the fibres. Post-growth Raman analysis shows characteristic features associated with high graphitic ordering which turn an intrinsically insulating substrate into an electrically conductive (∼260 S/m) fabric, thus suggesting the possibility to employ the newly engineered hierarchical fabric in all those applications where the combination of good mechanical properties and electrical conductivity is a key requirement.

Fast room-temperature hydrogenation of nitroaromatics on Pd nanocrystal-boron cluster/graphene oxide nanosheets

The reduction of nitroaromatics to aminoaromatics is essential for fine chemical production and effective sewage treatment. However, the activity of an external catalyst is essential for the reaction. In this study, Pd nanocrystals were anchored in situ on two-dimensional graphene oxide (GO), which acted as a catalyst support with high specific surface area. The oxygen-containing groups on the surface of GO bonded to the functionally rich boron clusters through hydrogen bonding interactions. A mildly reducible closed-dodecahydrododecaboric acid anion cluster (closo‑[B12H12]2–) was employed as the target site. The mild reducibility of closo‑[B12H12]2– resulted in a wide dispersion of ultrafine Pd nanocrystals on GO. Under ambient conditions, Pd/BGO rapidly hydrogenated nitroaromatics, such as 4-nitrophenol, to aminoaromatics with approximately 100% efficiency. Moreover, Pd/BGO retained its high catalytic activity for the hydrogenation/reduction of 4-nitrophenol after five catalytic cycles. Therefore, Pd/BGO could be a promising and economically viable candidate for various practical applications. The proposed innovative preparation strategy and highly efficient catalytic activity suggested the effective performance of closo‑[B12H12]2– as nanometal nucleation target sites. In addition to providing an alternate route for preparing supported nanometals, this study presents a stable and efficient catalyst for the hydrogenation of nitroaromatics.

Dithiothreitol-Lucigenin Chemiluminescent System for Ultrasensitive Dithiothreitol and Superoxide Dismutase Detection.

1,4-Dithiothreitol (DTT), a highly water-soluble and well-known reducing agent for preservation and regeneration of sulfhydryl groups in biomedical applications, has been developed as an efficient and stable coreactant of lucigenin for the first time. DTT efficiently reacts with lucigenin to generate intense chemiluminescence (CL), eliminating the need for external catalysts to facilitate the lucigenin CL. The DTT-lucigenin CL is approximately 15-fold more intense when compared with the lucigenin-H2O2 classical system. Superoxide dismutase (SOD) remarkably quenches the DTT-lucigenin CL. Based on this phenomenon, a newly developed CL approach for the determination of SOD was proposed with a linear range of 0.01-1.5 μg/mL and a limit of detection of 2.2 ng/mL. Various factors affecting the CL emission of the DTT-lucigenin probe were studied and optimized. Plausible mechanistic pathways for the CL coreaction of lucigenin with DTT were proposed and fully discussed. Our proposed method not only has the merit of being selective toward the target analytes but also eliminates the need for the complex synthesis of luminescent probes and facilitates the sensitive detection of SOD in human serum and cosmetics SOD raw material with satisfactory recoveries.

Electrochemical Synthesis of Iodohydrins

AbstractIodohydrins and corresponding ethers were synthesized by an electrochemical process using inexpensive and non‐toxic ammonium iodide. This transformation was applied to a panel of alkenes, giving products without the need of external hazardous oxidants, reductants or metal catalyst. This protocol showed a general efficiency to synthesize valuable iodinated molecules with yields from 19% to 90%.magnified image

Metal-Free Temperature-Controlled Intermolecular [3 + 2] Annulation to Access Benzo[d]thiazole-2(3H)-thiones and Benzo[d]thiazol-2(3H)-ones.

A facile access to benzo[d]thiazole-2(3H)-thiones and benzo[d]thiazol-2(3H)-ones has been developed through a temperature-controlled intermolecular [3 + 2] annulation of N,N-disubstituted arylhydrazines with CS2 in the presence of DMSO. This protocol can obviate the prefunctionalization of the starting materials. This direct C-S/C-N bond formation reaction was performed in the absence of any external catalysts, transition metals, bases, ligands, and oxidants with high step economy.

Facile and general electrochemical deuteration of unactivated alkyl halides

Herein, a facile and general electroreductive deuteration of unactivated alkyl halides (X = Cl, Br, I) or pseudo-halides (X = OMs) using D2O as the economical deuterium source was reported. In addition to primary and secondary alkyl halides, sterically hindered tertiary chlorides also work very well, affording the target deuterodehalogenated products with excellent efficiency and deuterium incorporation. More than 60 examples are provided, including late-stage dehalogenative deuteration of natural products, pharmaceuticals, and their derivatives, all with excellent deuterium incorporation (up to 99% D), demonstrating the potential utility of the developed method in organic synthesis. Furthermore, the method does not require external catalysts and tolerates high current, showing possible use in industrial applications.

Agro-Waste Sourced Catalyst as an Eco-Friendly and Sustainable Approach for Knoevenagel Condensation Reaction

Background: The present work describes an eco-friendly and sustainable approach for the Knoevenagel condensation of an aromatic aldehyde with ethyl cyanoacetate, and salicylaldehyde with Meldrum acid for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin (2-oxo-2H-1-benzopyran) derivatives, respectively. The reaction was performed under green catalytic media-Water Extract of Watermelon Fruit Peel Ash (WEWFPA), which is an eco-friendly protocol derived from the agro-waste feedstock. Various protocols have been reported for the synthesis of Knoevenagel condensation reaction using a hazardous catalyst or/and solvents found toxic to the environment, requiring longer reaction time, giving poor yield, and requiring purification of the final product. The method at hand provides several added advantages like: being a completely green method, economic, inexpensive catalyst, and the final product isolated is in pure form with good yield. Objective: The objective of the study was to develop a green methodology for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives. Results: The agro-waste based catalyst developed in the present study avoids the use of external inorganic/ organic bases and additives. Knoevenagel condensation of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives is carried out under room temperature using microwave irradiation, which is a solvent-free synthesis, requiring less time and giving better yield. Methods: We have demonstrated that WEWFPA can be employed as a green homogenous agrowaste for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives under rt stirring and microwave irradiation in a very economical way. The developed method is found to be simple and robust, non-hazardous and solvent-free to obtain the target product. Conclusion: In conclusion, we have established an efficient, simple, agro-waste based catalytic approach for the synthesis of ethylbenzylidenecyanoacetate and 3-carboxy coumarin derivatives employing WEWFPA as an efficient catalyst under rt stirring and microwave synthesis. The method is a green, economical and eco-friendly approach for the synthesis of Knoevenagel condensation products. The advantages of the present approach are that the reaction is a solvent-free synthesis, requiring no external metal catalyst, chemical base free, short reaction time and excellent yield of product. The catalyst is agro-waste derived, which is abundant in nature, thus making the present approach a greener one.

Teaching an Old Compound New Tricks: Reversible Transamidation in Maleamic Acids.

Dynamic combinatorial chemistry is a method widely used for generating responsive libraries of compounds, with applications ranging from chemical biology to materials science. It relies on dynamic covalent bonds that are able to form in a reversible manner in mild conditions, and therefore requires the discovery of new types of these bonds in order to progress. Amides, due to their high stability, have been scarcely used in this field and typically require an external catalyst or harsh conditions for exchange. Compounds able to undergo uncatalysed transamidation at room temperature are still rare exceptions. In this work, we describe reversible amide formation and transamidation in a class of compounds known as maleamic acids. Due to the presence of a carboxylic acid in β‐position, these compounds are in equilibrium with their anhydride and amine precursors in organic solvents at room temperature. First, we show that this equilibrium is responsive to external stimuli: by alternating the additions of a Brønsted acid and a base, we can switch between amide and anhydride several times without side‐reactions. Next, we prove that this equilibrium provides a pathway for reversible transamidation without any added catalyst, leading to thermodynamic distributions of amides at room temperature. Lastly, we use different preparation conditions and concentrations of Brønsted acid to access different library distributions, easily controlling the transition between kinetic and thermodynamic regimes. Our results show that maleamic acids can undergo transamidation in mild conditions in a reversible and tunable way, establishing them as a new addition to the toolbox of dynamic combinatorial chemistry.

Preparation of Vanillin Derivatives Based on Schiff Base Reaction

This study introduced the aldehyde monomer derived from vanillin (4,4-[(1,4-phenylenedimethylene) dioxy] -bis (3-methoxybenzaldehyde), BA), followed by reaction with tris (2-aminoethyl) amine (TA) and diamine (DA) to prepare a series of polyimine films (BADT-X). By adjusting the ratio of TA and DA, BADT-X with different degrees of cross-linking can be obtained, thereby the performance of the film could be tuned. The physical results show that with the increase of TA content, the mechanical performance of BADT-X has been improved from 31.20 to 45.95MPa, furthernore, the degradation temperature (Td5%) increased from 166.66 to 272.80 °C, and the char yield of all BADT-x was more than 45% at 600 °C. Meanwhile, the quick reshape properties of this polyimine film can be accomplished without any external catalyst in 5 mins at elevated temperature.

High efficient crosslinking of gelatin and preparation of its excellent flexible composite film using deep eutectic solvent

To overcome the gelation of gelatin at low temperatures, solve the brittleness of gelatin-based films and improve the reaction efficiency between the components, a facile design strategy is proposed for preparing gelatin/polyvinyl alcohol composite films (Gel-PVAs) with excellent flexibility. During the preparation process, sodium acetate trihydrate/urea deep eutectic solvent (SAT/U-DES) was introduced to dissolve the gelatin, which not only exhibited the higher crosslinking efficiency but also induced the plasticizing effect to the composite film. When the DES mass fraction was 60%, the solubility of the gelatin was up to 25%, and gelation did not occur at room temperature. In addition, the elongation at break of the Gel-PVA60 film reached up to 654%, which was a 631% increase when compared with that of the Gel-PVA0 film. These remarkable properties were due to the formation of new H-bonds with the groups in gelatin molecules induced by SAT/U-DES, which limited the reformation of the gelatin structures after cooling and improved the flexibility and ductility of the film. Moreover, the destruction of interchain interactions between the gelatin molecules allowed more carboxyl groups to react with PVA in the crosslinking modification system, which resulted in an improvement of the reaction efficiency without external catalysts.

Transition Metal‐Free, Visible Light‐Mediated Radical Cyclisation of Malonyl Radicals onto 5‐Ring Heteroaromatics

AbstractAnnulated heteroaromatics can be accessed through the addition of malonyl radicals onto heterocycles. Current methods are applicable to electron‐rich heteroaromatics and reliant on transition metals or toxic tin reagents. Here we report a metal‐free, visible light‐mediated cyclisation of malonates onto 5‐ring heteroaromatics using iodomalonates as key intermediates. The iodomalonates are prepared and photolysed in situ to give the desired annulated products, in yields of 46–94% without the need for external catalysts. The scope of this transformation includes N‐alkyl, N‐acyl and carbon‐tethered malonates adding onto a wide range of 5‐membered heteroaromatics.magnified image

Electrocatalytic Isomerization of Allylic Alcohols: Straightforward Preparation of β-Aryl-Ketones

Electrochemical synthesis has been rapidly developing over the past few years. Here, we report a practical and eco-friendly electrocatalytic isomerization of allylic alcohols to their corresponding carbonyl compounds. This reaction can be carried out in undivided cells without the addition of external chemical oxidants and metal catalysts. Moreover, this reaction features a broad substrate scope including challenging allylic alcohols bearing tri- and tetra-substituted olefins and affords straightforward access to diverse β-aryl-ketones. Mechanistic investigations suggest that the reactions proceed through a radical process. This study represents a unique example in which electrochemistry enables hydrogen atom transfer in organic allylic alcohol substrates using a simple organocatalyst.

Synthesis of Super-Long Carbon Nanotubes from Cellulosic Biomass under Microwave Radiation.

This study reports a novel method for synthesizing super-long carbon nanotubes (SL-CNTs) from cellulose via a microwave treatment process without an external catalyst. CNTs with a length of 0.7–2 mm were obtained via microwave treatment of cellulose biochar temperatures of 1200–1400 °C. Scanning electron microscope (SEM), together with high-resolution transmission electron microscope (HRTEM) results, were used to investigate the changes in the length and morphology of CNTs with respect to treatment temperature. The morphology of CNTs changed from twisted, curved, and threadlike to straight structures. The average length of CNTs after microwave pyrolysis at 600 °C was approximately 600–1800 nm, which after microwave treatment at 1300 °C and 1400 °C increased to about 1–2 mm. X-ray diffractometer (XRD) results confirmed the crystalline structure of CNTs with two prominent peaks at 2θ = 26.3° and 2θ = 43.2° correlating with the graphite (002) and (100) reflections. The ID/IG ratio obtained from Raman spectra of the CNTs decreased to the lowest value of 0.84 after microwave treatment at 1400 °C, implying a high degree of carbon order. The presence of Fe and trace amounts of other elements were confirmed by the energy-dispersive X-ray spectrometer (EDS) and were postulated to have catalyzed the growth of CNTs. The mechanism of the SL-CNTs growth under microwave treatment was proposed and discussed.

Formation mechanism and influencing factors of dioxins during incineration of mineralized refuse

Chlorine sources and heavy metal catalysts play an important role in the formation of dioxins during the incineration of mineralized refuse in landfills. Through the use of different external chlorine sources and pretreatment methods, their effects on the formation of dioxins in flue gas from mineralized refuse incineration were studied. The effects of temperature, external chlorine sources, pretreatment methods and metal catalyst ratios on dioxin generation in the flue gas of mineralized refuse incineration were investigated with mineralized refuse. The effects of temperature, atmosphere and external chlorine source on the low-temperature re-synthesis of dioxins from mineralized refuse incineration fly ash were investigated, and the ability of re-synthesis of dioxins from mineralized refuse incineration fly ash and MSWI (Municipal Solid Waste Incineration) fly ash was compared using in situ XPS (X-ray Photoelectron Spectrometer) and heavy metal morphology analysis. The results showed that CuCl2 has the strongest catalytic effect on the formation of gaseous dioxin from mineralized refuse incineration. The components of mineralized refuse and water washing do not interfere with the mass concentration of dioxins in incinerated flue gas. The effect of temperature, atmosphere and external chlorine source on the low-temperature synthesis of dioxin from mineralized refuse incineration fly ash was similar to that of MSWI fly ash. The results of in situ XPS and speciation analysis of heavy metals show that the reducible metals in mineralized refuse fly ash was mainly composed of Fe. The stronger oxidation and chlorination of carbon and the stronger interaction between copper and iron in mineralized refuse fly ash make the dioxin synthesis capacity higher than that of MSWI fly ash. In addition, the concentration of gaseous dioxins produced by mineralized refuse incineration was directly proportional to the amount of CuCl2. However, changing the ratio of heavy metals weakened the de novo synthetic reaction to a certain extent, resulting in the change in 17 toxic dioxin isomers.

One-Step Grown Carbonaceous Germanium Nanowires and Their Application as Highly Efficient Lithium-Ion Battery Anodes.

Developing a simple, cheap, and scalable synthetic method for the fabrication of functional nanomaterials is crucial. Carbon-based nanowire nanocomposites could play a key role in integrating group IV semiconducting nanomaterials as anodes into Li-ion batteries. Here, we report a very simple, one-pot solvothermal-like growth of carbonaceous germanium (C-Ge) nanowires in a supercritical solvent. C-Ge nanowires are grown just by heating (380–490 °C) a commercially sourced Ge precursor, diphenylgermane (DPG), in supercritical toluene, without any external catalysts or surfactants. The self-seeded nanowires are highly crystalline and very thin, with an average diameter between 11 and 19 nm. The amorphous carbonaceous layer coating on Ge nanowires is formed from the polymerization and condensation of light carbon compounds generated from the decomposition of DPG during the growth process. These carbonaceous Ge nanowires demonstrate impressive electrochemical performance as an anode material for Li-ion batteries with high specific charge values (>1200 mAh g–1 after 500 cycles), greater than most of the previously reported for other “binder-free” Ge nanowire anode materials, and exceptionally stable capacity retention. The high specific charge values and impressively stable capacity are due to the unique morphology and composition of the nanowires.

Base‐Promoted Three‐Component Cyclization and Coupling Strategy for the Synthesis of Substituted 3‐Aryl‐5‐thio‐1,3,4‐thiadiazole‐2‐thiones

AbstractAn effective base‐promoted cyclization and coupling strategy for the construction of substituted 3‐aryl‐5‐thio‐1,3,4‐thiadiazole‐2‐thiones from phenylhydrazines, olefins and CS2 is developed through employing CS2 as a sulfur feedstock. The reaction proceeds under mild reaction conditions in the absence of any external catalysts, transition metals and ligands. The one‐step three‐component procedure also shows the merits of simple operation, using available starting materials, wide substrate scopes, and high atom and step economy. This reaction provides facile access to substituted 3‐aryl‐5‐thio‐1,3,4‐thiadiazole‐2‐thiones, which could be used in the field of drug research.

Effect of the precursor aggregate state on the synthesis of CNTs in a DC plasma jet

The transformation of various carbonaceous substances into ordered carbon nanostructures is a fundamental process in nanotechnology. Since this structural transformation is a common property of various methods for producing CNTs, understanding the mechanism of this process in the bulk of a plasma jet will be extremely important, since no substrates are used here. We present an experimental and numerical study of the synthesis of CNTs with and without external catalysts for the pyrolysis of soot, acetylene, and ethanol in a DC argon plasma at a pressure of 350 Torr. By combining various physical methods, including simultaneous thermal analysis, diffraction analysis, electron microscopy, and energy dispersive analysis, we will show that the aggregation state of the precursor significantly affects the structural and morphological properties of CNTs. Theoretical calculations under the assumption of local thermodynamic equilibrium made it possible to study the gas phase composition of a plasma flow in which the CNT precursor is nucleated. It was found that during the pyrolysis of soot (C), the condensation temperature of solid carbon is 3672 K, with the hydrogen in precursor (C2H2) it is lower and equals 3353 K, with the addition of oxygen (C2H5OH) its value becomes even <3141 K. At the lowest condensation temperature, the most thermally stable CNTs are formed.

Synthesis of Unsymmetrical Diarylfumaronitriles via Tandem Michael Addition and Oxidation under K3Fe(CN)6/O2 System.

An efficient formal alkenyl C-H cyanation reaction has been developed for the general synthesis of unsymmetrical diarylfumaronitriles in good to excellent yields. The reaction was achieved through tandem Michael addition and an oxidative process. The merits of this transformation include the use of K3Fe(CN)6 as a safe and nontoxic cyanide source, without an external noble metal catalyst, oxygen-involved reactions, easily available raw materials, good functional group tolerance, high stereoselectivity, and potential further application of the products.

Chemoselective Reduction of Fenofibric Acid to Alcohol in the Presence of Ketone by Mixed Anhydride and Sodium Borohydride.

A highly efficient and facile protocol for the selective reduction of carboxylic acid of Fenofibric acid to corresponding alcohol was developed. The selective reduction was carried out by activation of carboxylic acid by mixed anhydride followed by the reaction of sodium borohydride in presence of methanol. This is the first example of chemoselective reduction of carboxylic acid to alcohol in presence of a ketone without any external catalyst or ligand in a single step. The reaction offers wide applicability for the selective carboxylic group reduction methodology. The chemoselective reduction was demonstrated by the reduction of Fenofibric acid, an active metabolite of the drug Fenofibrate, to corresponding alcohol in excellent selectivity, yield, and purity.

Visible-light promoted photocatalyst-free aerobic α-oxidation of tertiary amines to amides.

A photocatalyst-free, visible-light-induced strategy for the α-oxygenation of tertiary amines by molecular oxygen (1 atm), enabled by electron-donor-acceptor (EDA) complexes, has been developed. This EDA-complex mediated process provides a facile access to amides and esters from readily accessible corresponding amines and ethers without the need for an external photoredox catalyst, and also features mild reaction conditions, broad substrate scope and excellent functional group compatibility. Mechanistic studies indicated a short radical chain reaction triggered by the decomposition of EDA complexes upon visible-light irradiation.