Vanadium-catalyzed Hydration of 2-Cyanopyrazine to Pyrazinamide with Unique Substrate Specificity

Pyrazinamide is an important medicine used for the treatment of tuberculosis(TB). The preparation of pyrazinamide via catalytic hydration of 2-cyanopyrazine is of great economic interest with high atomic economy. Heterogeneous non-precious transition metal-catalyzed hydration of nitriles under neutral reaction conditions would be rather attractive. Herein vanadium-nitrogen-carbon materials were fabricated and employed for selective hydration of nitriles using water as both the solvent and reactant. 2-Cyanopyrazine could be smoothly converted into to pyrazinamide with unique substrate specificity. Additives with different N and O atoms could significantly affect hydration of 2-cyanopyrazine due to competitive adsorption/coordination in the reaction system. This work provides a new approach for non-precious metal catalyzed hydration of nitriles.

Ag-embedded manganese oxide octahedral molecular sieve (Ag-OMS-2) nano-rods as efficient heterogeneous catalysts for hydration of nitriles to amides in aqueous solution

Silver-embedded manganese oxide octahedral molecular sieve (Ag-OMS-2) nano-rods were synthesized using a pre-incorporation approach, and unambiguously characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). A highly uniform distribution of Ag nanoparticles embedded in the porous structure of OMS-2, was found to be in favor of high catalytic activity of the composite for hydration of nitriles to corresponding amides in aqueous solution. By using a catalyst dosage of 30 mg per mmol of substrate, in the temperature range of 80-100 °C, and reaction times of 4-9 h, excellent yields (73-96%) of the desired amides (13 examples) were obtained. Also, the catalyst was easy to recycle, and showed a slight decrease in efficiency after six consecutive runs.

A Molecular Hybrid of an Atomically Precise Silver Nanocluster and Polyoxometalates for H2 Cleavage into Protons and Electrons

Atomically precise silver (Ag) nanoclusters are promising materials as catalysts, photocatalysts, and sensors because of their unique structures and mixed-valence states (Ag⁺ /Ag⁰ ). However, their low stability hinders the in-depth study of their intrinsic reactivity and catalytic property accompanying their redox processes. Herein, we demonstrate that a molecular hybrid of an atomically precise {Ag₂₇ }¹⁷⁺ nanocluster and polyoxometalates (POMs) can efficiently cleave H₂ into protons and electrons. The Ag nanocluster accommodates electrons through the redox reaction from {Ag₂₇ }¹⁷⁺ to {Ag₂₇ }¹³⁺ , and the POM ligands play the following important roles: (i) a significant stabilization of the typically unstable Ag nanocluster to preserve its structure during the redox reaction with H₂ , (ii) formation of a unique interface between the Ag nanocluster and metal oxides for efficient H₂ cleavage, and (iii) storage of the generated protons on the negatively charged basic surface.

N-Functionalised Imidazoles as Stabilisers for Metal Nanoparticles in Catalysis and Anion Binding

Metal nanoparticles (NPs) have physicochemical properties which are distinct from both the bulk and molecular metal species, and provide opportunities in fields such as catalysis and sensing. NPs typically require protection of their surface to impede aggregation, but these coatings can also block access to the surface which would be required to take advantage of their unusual properties. Here, we show that alkyl imidazoles can stabilise Pd, Pt, Au, and Ag NPs, and delineate the limits of their synthesis. These ligands provide an intermediate level of surface protection, for which we demonstrate proof‐of‐principle in catalysis and anion binding.

Chemoselective reduction of nitro and nitrile compounds using an Fe3O4-MWCNTs@PEI-Ag nanocomposite as a reusable catalyst

Chemoselective reductions by an Fe₃O₄-MWCNTs@PEI-Ag nanocomposite.

Solvent-tailored Pd3P0.95 nano catalyst for amide-nitrile inter-conversion, the hydration of nitriles and transfer hydrogenation of the C[double bond, length as m-dash]O bond

For the first time, a one pot thermolysis of [Pd(PPh3)2Cl2] prepared by reacting Ph3P with PdCl2 in a 2 : 1 molar ratio in MeOH at 280 °C in a trioctylphosphine (TOP) and oleylamine(OA)-octadecane(ODE) mixture (1 : 1) was used to prepare quantum dots (QDs; size ∼2-3 nm) and nanoparticles (NPs; size ∼13-14 nm), respectively, of composition Pd3P0.95. TEM, SEM-EDX, powder-XRD and XPS (for QDs only) were used to authenticate the two nanophases. 31P{1H}NMR experiments performed to monitor the progress of thermolysis reactions revealed that the phosphorus present in the Pd3P0.95 QDs had come from TOP, whereas in Pd3P0.95 NPs, its source is triphenylphosphine. The nature of the solvent did not affect the chemical composition of the nano-phase but controlled its size. Probably, solvent dependent, unique, single source precursors (SSPs) of palladium were generated in situ, and controlled the size. The catalytic activity of both Pd3P0.95 QDs and NPs was explored. The QDs were found to be efficient as a catalyst for the amide-nitrile interconversion at room temperature (yield up to 92% in 4 h), hydration of nitriles and transfer hydrogenation (TH) of carbonyl compounds with yields up to 96% in 3-4 h. The yields and reaction rates of amide-nitrile inter-conversion and TH when catalyzed by Pd3P0.95 QDs were found to be higher compared to the ones observed with the Pd/C catalyst. The binding energy of Pd(3d) in the X-ray photoelectron spectrum (XPS) of Pd3P0.95 indicated an electron transfer from the metal to phosphorus, resulting in electron deficient palladium, which facilitates the coordination of a substrate to Pd and drives the reaction. The reusability of Pd3P0.95 QDs for the interconversion was found to be up to 4-times, while for the transfer hydrogenation of carbonyl compounds it was up to 6-times, but with a diminished yield. Pd3P0.95 NPs were found to be less active (yield up to 36% in optimized reaction conditions) in comparison to Pd3P0.95 QDs. The mercury poisoning test suggested that the catalysis predominantly proceeded heterogeneously on the surface of the QDs. The PXRD and XPS results did not suggest a significant variation in the phase of QDs after the third catalytic cycle. The bleeding of Pd during catalysis (determined by flame AAS) and the agglomeration of QDs as supported by the SEM-EDX and TEM results are probably responsible for the reduction in the catalytic activity of QDs after reusing three times.

Waste-to-wealth: biowaste valorization into valuable bio(nano)materials

The waste-to-wealth concept aims to promote a future sustainable lifestyle where waste valorization is seen not only for its intrinsic benefits to the environment but also to develop new technologies, livelihoods and jobs.

Strategies towards the synthesis of anti-tuberculosis drugs

In this report, we reviewed the strategies towards the synthesis of anti-tuberculosis drugs. They include semisynthetic approaches, resolution based strategies, microbial transformations, solid phase synthesis, and asymmetric synthesis.

Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

A facile single-step synthesis of polyvinylpyrrolidone-silver nanocomposites using a conventional spray dryer

We have developed a facile single-step synthesis of silver nanocomposite using a conventional spray dryer. We investigated the synthetic conditions by controlling the concentrations of the chemical reactants. Further, we confirmed the effect of the molecular weight of polyvinylpyrrolidones, and revealed that the molecular weight significantly affected the properties of the resultant silver nanocomposites. The long-term stability of the silver nanocomposites was tested, and little change was observed, even after storage for three months. Most of all, the simple commercial implementation, in combination with large-scale synthesis, possesses a variety of advantages, compared to conventional complicated and costly dry-process synthesis methods. Thus, our method presents opportunities for further investigation, for both lab-scale studies and large-scale industrial applications.

Triflic acid-catalyzed metal-free synthesis of (E)-2-cyanoacrylamides and 3-substituted azetidine-2,4-diones

A TfOH-catalyzed highly efficient synthesis of biologically active (E)-2-cyanoacrylamides and 3-substituted azetidine-2,4-diones has been reported with 64–94% yields under metal-free conditions.

Water-soluble superbulky (η6-p-cymene) ruthenium(ii) amine: an active catalyst in the oxidative homocoupling of arylboronic acids and the hydration of organonitriles

Water-soluble superbulky (η⁶-p-cymene) ruthenium(ii) amine complex mediated oxidative homocoupling of arylboronic acids and the hydration of organonitriles are reported.

Metal-Free Thermal Activation of Molecular Oxygen Enabled Direct α-CH2-Oxygenation of Free Amines

Direct oxidation of α-CH₂ group of free amines is hard to achieve due to the higher reactivity of amine moiety. Therefore, oxidation of amines involves the use of sophisticated metallic reagents/catalyst in the presence or absence of hazardous oxidants under sensitive reaction conditions. A novel method for direct C-H oxygenation of aliphatic amines through a metal-free activation of molecular oxygen has been developed. Both activated and unactivated free amines were oxygenated efficiently to provide a wide variety of amides (primary, secondary) and lactams under operationally simple conditions without the aid of metallic reagents and toxic oxidants. The method has been applied to the synthesis of highly functionalized amide-containing medicinal drugs, such as O-Me-alibendol and -buclosamide.

Catalytic Organic Reactions in Water toward Sustainable Society

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the "watershed" in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Hemilability-Driven Water Activation: A NiII Catalyst for Base-Free Hydration of Nitriles to Amides

The Ni^II complex 1 containing pyridyl- and hydroxy-functionalized N-heterocyclic carbenes (NHCs) is synthesized and its catalytic utility for the selective nitrile hydration to the corresponding amide under base-free conditions is evaluated. The title compound exploits a hemilabile pyridyl unit to interact with a catalytically relevant water molecule through hydrogen-bonding and promotes a nucleophilic water attack to the nitrile. A wide variety of nitriles is hydrated to the corresponding amides including the pharmaceutical drugs rufinamide, Rifater, and piracetam. Synthetically challenging α-hydroxyamides are accessed from cyanohydrins under neutral conditions. Related catalysts that lack the pyridyl unit (i.e., compounds 2 and 4) are not active whereas those containing both the pyridyl and the hydroxy or only the pyridyl pendant (i.e., compounds 1 and 3) show substantial activity. The linkage isomer 1' where the hydroxy group is bound to the metal instead of the pyridyl group was isolated under different crystallization conditions insinuating a ligand hemilabile behavior. Additional pK_a measurements reveal an accessible pyridyl unit under the catalytic conditions. Kinetic studies support a ligand-promoted nucleophilic water addition to a metal-bound nitrile group. This work reports a Ni-based catalyst that exhibits functional hemilability for hydration chemistry.

Poly(amic acid) salt-stabilized silver nanoparticles as efficient and recyclable quasi-homogeneous catalysts for the aqueous hydration of nitriles to amides

The reversible pH-response of the Ag–PAAS catalyst allows it to catalyze the selective hydration of various nitriles quasi-homogeneously in water and to be easily recovered by simply adjusting the pH value of the solution.

Transamidation catalysed by a magnetically separable Fe3O4 nano catalyst under solvent-free conditions

Transamidation catalysed by magnetically separable Fe₃O₄ nano catalyst under solvent-free condition.

A convenient ‘NOSE’ approach used towards the synthesis of 6-amino-1,3-dimethyl-5-indolyl-1H-pyrimidine-2,4-dione derivatives catalyzed by nano-Ag

Uracil derivatives were synthesized in high yield catalyzed by reusable nano-Ag at 70 °C upon reacting 6-amino-1,3-dimethyluracil and indole derivatives.