Reduction Of Nitroaromatics Research Articles

Self‐Assembled Magnetic Gold Catalysts from Dual‐Functional Boron Clusters

AbstractA new class of core–shell magnetic gold nanocomposites is prepared in a raspberry‐like fashion by the controlled supramolecular host–guest assembly of γ‐cyclodextrins (γ‐CDs) and boron clusters. In this work, Cs2[closo‐B12H12], a fundamental boron cluster, can play a dual role in the preparation of highly monodispersed Au nanoparticles and in the immobilization of Au nanoparticles on the γ‐CDs@Fe3O4 surface as an effective anchor. This facile and spontaneous supramolecular strategy allows for the control of the size and composition of the highly stable gold composites. Furthermore, the obtained AuNPs@Fe3O4 composites exhibit an excellent catalytic activity and recyclability for the selective reduction of nitroaromatics to their corresponding aniline compounds, and the fastest reaction can be achieved within 20 s with a high conversion and selectivity at room temperature, which is better than that obtained previously in studies on metal nanoparticle composites as catalysts.

Textile-Supported Silver Nanoparticles for Nitroaromatic Reduction

Textile-Supported Silver Nanoparticles for Nitroaromatic Reduction

Aloe-vera flower shaped rutile TiO2 for selective hydrogenation of nitroaromatics under direct sunlight irradiation

This study reveals the fabrication of a sunlight receptive flower shaped rutile TiO2 microstructure (F-TiO2) for the selective photoreduction of nitroaromatics. The crystalline F-TiO2 possesses small band gap (∼2.8 eV) and large specific surface area (193 m2g−1). Moreover, the F-TiO2 exhibited higher relaxation time (120 µs) for the electron-hole pairs due to its brilliant multi dimensional morphology that enables shorter diffusion path and multiple scattering of active sites. The experimental results revealed the superior photocatalytic activity of the F-TiO2 microstructure in contrast to active P25 and rutile TiO2 (obtained from thermally treated P25 at 800 °C for 4 h) for the reduction of nitrobenzene, m-dinitrobenzene and 2,2-dinitrobiphenyl in 50% aqueous isopropanol (hole scavenger) to aniline (42–72%), m-nitroaniline (37–42%), m-phenylenediamine (88–100%) and benzo[c]cinnoline (80–94%) respectively under UV and direct sunlight irradiation. The quantitative estimation of byproducts like acetone and hydrogen (H2) produced from iso-propanol oxidation and water splitting during instant reduction of nitroaromatics to aromatic amines is well correlated and explained on the basis of its beneficial surface structural and electronic properties.

Induction of Catalytic Activity in ZnO Loaded Cobalt Based MOF for the Reduction of Nitroarenes

AbstractAmalgamating the robust structures of metal organic frameworks with nanoparticles is one of the most devisable and logical approach in order to enhance their applicability. We report herein an easy wet impregnation method for loading ZnO nanoparticles with tunable sizes and shapes on a cobalt based metal organic framework constructed by using CoCl2.6H2O and 4, 4’‐oxy‐bis (benzoic acid) (OBA). The size, composition and morphology of nanoparticles were characterized using powder X‐ray diffraction (P‐XRD), energy dispersive X‐ray spectroscopy (EDX), high resolution transmission electron microscopy (HR‐TEM), Raman spectroscopy, X‐ray Photoelectron spectroscopy (XPS) and UV‐Diffuse reflectance spectroscopy. The incorporation of nanoparticles does not affect the overall structural integrity of the framework whereas it induces the heterogenous catalytic capability for the reduction of nitro aromatics to their corresponding amines under benign conditions, which cannot be realized using bare MOF.

Cu-catalyzed reduction of azaarenes and nitroaromatics with diboronic acid as reductant

A ligand-free copper-catalyzed reduction of azaarenes with diboronic acid as reductant in an aprotic solvent under mild conditions has been developed. Most interestingly, the nitroazaarenes could be reduced exclusively to give the corresponding amines without touching the azaarene moieties. Furthermore, the reductive amination of aromatic nitro compounds and aromatic aldehydes has also been realized. A series of hydrogenated azaarenes and secondary amines were obtained with good functional group tolerance.

Synthesis and characterization of copper nanoparticles on walnut shell for catalytic reduction and C-C coupling reaction

Walnut shell-stabilized copper nanoparticles (CuNP/WS) were successfully prepared by a simple reaction of copper sulfate and Sodium borohydride. Formation of copper nanoparticles in this bio-nanocomposite was observed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscope (EDX). CuNP/WS was found to be an efficient, inexpensive, easy to prepare, green and reusable catalyst in the reduction of aromatic nitro and nitrile compounds to their corresponding amines with NaBH4 at 35 °C in aqueous medium. We continued our studies on the application of this nanocomposite in the classic Ullman reaction to synthesize biaryl. This method has the advantages of high yields, elimination of expensive stabilizer and homogeneous catalysts, simple methodology and easy work up. The catalyst can be recovered from the reaction mixture and reused several times without any significant loss of catalytic activity.

Informing Efforts to Develop Nitroreductase for Amine Production.

Nitroreductases (NRs) hold promise for converting nitroaromatics to aromatic amines. Nitroaromatic reduction rate increases with Hammett substituent constant for NRs from two different subgroups, confirming substrate identity as a key determinant of reactivity. Amine yields were low, but compounds yielding amines tend to have a large π system and electron withdrawing substituents. Therefore, we also assessed the prospects of varying the enzyme. Several different subgroups of NRs include members able to produce aromatic amines. Comparison of four NR subgroups shows that they provide contrasting substrate binding cavities with distinct constraints on substrate position relative to the flavin. The unique architecture of the NR dimer produces an enormous contact area which we propose provides the stabilization needed to offset the costs of insertion of the active sites between the monomers. Thus, we propose that the functional diversity included in the NR superfamily stems from the chemical versatility of the flavin cofactor in conjunction with a structure that permits tremendous active site variability. These complementary properties make NRs exceptionally promising enzymes for development for biocatalysis in prodrug activation and conversion of nitroaromatics to valuable aromatic amines. We provide a framework for identifying NRs and substrates with the greatest potential to advance.

Enhanced Nitrobenzene reduction by zero valent iron pretreated with H2O2/HCl

In this study a novel iron-based reducing agent of highly effective reduction toward nitrobenzene (NB) was obtained by pretreating zero valent iron (ZVI) with H2O2/HCl. During the H2O2/HCl pretreatment, ZVI undergoes an intensive corrosion process with formation of various reducing corrosion products (e.g., Fe2+, ferrous oxides/hydroxides, Fe3O4), yielding a synergetic system (prtZVI) including liquid, suspensions and solid phase. The pretreatment process remarkably enhances the reductive performance of ZVI, where a rapid reduction of NB (200 mg L−1) in the prtZVI suspension was accomplished in a broad pH range (3–9) and at low dosage. Nitrosobenzene and phenylhydroxylamine are identified as the intermediates for NB reduction with the end-product of aniline. Compared with the virgin ZVI as well as another nanosized ZVI, the prtZVI system exhibits much higher electron efficiency for NB reduction as well as higher utilization ratio of Fe0. A rapid reduction of various nitroaromatics in an actual pharmaceutical wastewater further demonstrated the feasibility of the prtZVI system in real wastewater treatment.

Photosynthesis of silver nanoparticles using Durio zibethinus aqueous extract and its application in catalytic reduction of nitroaromatics, degradation of hazardous dyes and selective colorimetric sensing of mercury ions

A simple green route was reported to prepare highly stable silver nanoparticles. The aqueous leaf extract of Durio zibethinus reduces Ag+ to Ag0 in the presence of natural sunlight. The capping and stabilization of dAgNPs by the phytoconstituents of Durio zibethinus was confirmed by FTIR. TEM confirms that the dAgNPs are spherical in shape with a size range between 10–25 nm. XRD pattern confirmed that the dAgNPs are arranged in the face-centred cubic structure. The catalytic activity of the dAgNPs was proved by sodium borohydride mediated reduction of nitro aromatic compounds and degradation hazardous organic dyes. The reaction kinetics was analysed by pseudo-first order equation. Regardless of the efficacy of degrading organic dyes, we showed by zebrafish mortality assay that the toxicity of the dye degraded water reduced drastically. Besides catalysis, the dAgNPs has the potential to selective colorimetric sensing of hazardous mercury ion in aqueous solution.

Textile-supported silver nanoparticles as a highly efficient and recyclable heterogeneous catalyst for nitroaromatic reduction at room temperature.

A novel textile-based nanosilver catalyst was prepared with a facile synthetic method. The textile-supported nanosilver (TsNS) proved to be an excellent heterogeneous catalyst for the reduction of nitroaromatics with a broad substrate scope. It can be recycled for up to 6 times without significantly compromising its catalytic efficacy. The TsNS catalyst was developed into a column reactor, demonstrating its practical application with the advantages of low cost, ease of operation and large scale synthesis capabilities. Scanning electron microscopy (SEM) showed that there were few changes to the catalyst's surface after the reaction. Besides, inductively coupled plasma (ICP) analysis showed that few silver particles leaked, and the interactions between the nitro groups of the nitroaromatics and the nanosilver particles were characterized by X-ray photoelectron spectroscopy (XPS), which lead to the proposal of a four-step mechanism for the reduction reaction.

Magnetically retrievable nanocomposite adorned with Pd nanocatalysts: efficient reduction of nitroaromatics in aqueous media

Herein, we describe the fabrication of a magnetically retrievable nanocomposite adorned with highly active Pd nanoparticles (NPs) (MRN-Pd), which is useful for the efficient reduction of nitroaromatics in aqueous solution.

Reducing the barrier effect of graphene sheets on a Ag cocatalyst to further improve the photocatalytic performance of TiO2.

Graphene-based cocatalysts can improve the photocatalytic properties of semiconductors, but sometimes, they also function as barrier-like materials, influencing the photoactivity of composites. However, in a multi-cocatalyst system, less attention is paid to these negative effects of graphene on the performance of other cocatalysts. In this study, by adjusting the loading sequence of graphene and Ag cocatalyst on the surface of TiO2 spheres, the barrier effect of graphene sheets on Ag nanoparticles could be controlled effectively. As a result, these ternary composites with almost no Ag nanoparticles wrapped by graphene possessed improved properties for the photocatalytic reduction of nitro-aromatics as compared to those with some Ag nanoparticles covered by graphene. Furthermore, this phenomenon of barrier effect caused by graphene could be found in the control reaction with metal silver as the main catalyst; this indicated that by avoiding the possible negative influence of graphene on other cocatalysts, the properties of composites with graphene-containing multi cocatalysts could be further improved.

Gold nanodots self-assembled polyelectrolyte film as reusable catalyst for reduction of nitroaromatics

Separation of homogeneous catalyst from the reaction mixture is a crucial and difficult process in any catalytic process. To address this issue, a new class of multifunctional catalyst in the form of film was developed using a facile approach to enjoy the advantages of homogeneous catalyst with the versatility of heterogeneous catalyst. To achieve the same, methionine-capped gold nanodots (AuNDs) were self-assembled on a cationic polyelectrolyte modified glass plate for the catalytic reduction of nitro functional groups in the presence of olefinic double bond at mild conditions. Separation of this reusable catalytic film from the reaction mixture is very simple and advantageous when compared to the currently available and conventional catalytic systems. Kinetics of nitro reduction was monitored using absorption spectroscopy and the product formation was confirmed by $$^{1}\hbox {H}$$ and $$^{13}\hbox {C}\,\hbox {NMR}$$ analyses. Prepared AuNDs catalyst was characterized using UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), cyclic voltammetry and atomic force microscopy (AFM) techniques. SYNOPSIS Colloidal gold nanoparticles are efficient catalysts for organic reactions. But the removal of homogeneous gold colloids from the reaction mixture is very difficult. To address this issue, gold nanodots were synthesized and self-assembled over polyelectrolyte film to form catalytic plates. Removal of these reusable catalytic plates from the reaction mixture is facile.

Synthesis of bimetallic Au-Ag alloyed mesocomposites and their catalytic activity for the reduction of nitroaromatics

Homogeneously dispersed Au-Ag alloyed nanostructures varying from spherical (6–8 nm) to rod shape (aspect ratio ∼15–20 nm) were synthesized within the channels of amine modified mesoporous SBA-15 using post modification. Formation of alloy nanostructures for varying Au-Ag loadings have been supported by XPS and elemental mapping studies. Furthermore, changes in the surface/electronic properties of mesocomposites as a function of increased bimetallic Au:Ag loading have been elucidated with the help of XRD, BET, TEM and XPS studies respectively. It was found that synergism owing to electronic interplay between Au and Ag species concurrently improved the catalytic activity of bimetallic nanocomposites. Among the various monometallic and bimetallic mesocomposites, Au-Ag (5:1)/m-SBA-15 nanocomposites exhibited the best catalytic activity (k = 2.12 × 10−2 min−1 and 3.99 × 10−2 min−1) for the selective reduction of nitrobenzene to aniline and p-nitroacetophenone to p-aminoacetophenone respectively.

Room Temperature Reduction of Nitroaromatics Using Pd Nanoparticles Stabilized on Nano‐CeO2

AbstractPalladium nanoparticles stabilized on mesoporous cerium oxide nanoparticles catalyze the reduction of substituted nitroaromatics in presence of sodium borohydride as reductant. A modified two‐step methodology was developed for the synthesis of Pd/CeO2 nanoparticles. First the support CeO2 was synthesized by conventional precipitation method using ammonium oxalate as precipitant and Pd/CeO2 nanoparticles were prepared by hydrothermal treatment. The nanoparticles exhibit excellent catalytic activity and chemoselectivity for the reduction of nitroaromatics towards corresponding amine derivatives at room temperature. A kinetic study suggests that the reaction follows pseudo‐first order rate equation. Thus, synthesized catalyst represents significant role for the reduction of nitroaromatic compounds to value added amino compounds.

Composite of Au-Pd nanoalloys/reduced graphene oxide toward catalytic selective organic transformation to fine chemicals

A facile, stabilizing-molecules-free strategy has been utilized for anchoring Au-Pd alloy nanoparticles onto the flat surface of two-dimensional (2D) reduced graphene oxide (RGO) nanosheets. Formation of Au-Pd nanoalloys and loading onto the RGO are accomplished simultaneously. The Au-Pd/reduced graphene oxide (Au-Pd/RGO) exhibits higher catalytic activity than both Au/RGO and Pd/RGO, prepared by the same approach toward selective oxidation of benzyl alcohol and selective reduction of nitroaromatics, the catalytic activity order can be in good agreement with the noble metal particles size distribution of the Au, Pd and Au-Pd/RGO.

Dendrimer encapsulated Silver nanoparticles as novel catalysts for reduction of aromatic nitro compounds

Polyethylene glycol (PEG) core dendrimer encapsulated silver nanoparticles (AgNPs) were synthesized through normal chemical reduction method, where dendrimer acts as reducing and stabilizing agent. The encapsulated AgNPs were well characterized using TEM, DLS and XPS techniques. The synthesized AgNPs showed excellent catalytic activity towards the reduction of aromatic nitro compounds with sodium borohydride as reducing agent and the results substantiate that dendrimer encapsulated AgNPs can be an effective catalyst for the substituted nitro aromatic reduction reactions. Also the kinetics of different nitro compounds reductions was studied and presented.

Catalytic Reduction of Toxic Nitroarenes in Aqueous Medium Using Worm‐Like Rhodium Nanoparticles

AbstractWe demonstrate a facile synthesis of worm‐like rhodium nanoparticle stabilized by octadecylamine. This worm‐like nanoparticle exhibits excellent catalytic activity toward the reduction of nitro aromatics in the presence of NaBH4 in aqueous medium at room temperature. The reaction follows pseudo‐first order kinetics with a rate constant of 0.0216 s−1. We have explored this catalytic activity for the reduction of several nitro derivatives. This catalyst can effectively reduce toxic nitro aromatics in aqueous medium in much faster rate compared to other Rh‐based catalysts.

Accelerated removal of high concentration p-chloronitrobenzene using bioelectrocatalysis process and its microbial communities analysis

p-Chloronitrobenzene (p-CNB) is a persistent refractory and toxic pollutant with a concentration up to 200 mg/L in industrial wastewater. Here, a super-fast removal rate was found at 0.2–0.8 V of external voltage over a p-CNB concentration of 40–120 mg/L when a bioelectrochemical technology is used comparing to the natural biodegradation and electrochemical methods. The reduction kinetics (k) was fitted well according to pseudo-first order model with respect to the different initial concentration, indicating a 1.12-fold decrease from 1.80 to 0.85 h−1 within the experimental range. Meanwhile, the highest k was provided at 0.5 V with the characteristic of energy saving. It was revealed that the functional bacterial (Propionimicrobium, Desulfovibrio, Halanaerobium, Desulfobacterales) was selectively enriched under electro-stimulation, which possibly processed Cl-substituted nitro-aromatics reduction. The possible degradation pathway was also proposed. This work provides the beneficial choice on the rapid treatment of high-concentration p-CNB wastewater.

Molybdenum-Catalyzed Synthesis of Nitrogenated Polyheterocycles from Nitroarenes and Glycols with Reuse of Waste Reduction Byproduct.

A novel domino reduction/imine formation/intramolecular cyclization/oxidation for the efficient synthesis of pyrrolo(indolo)[1,2-a]quinoxalines and pyrrolo(indolo)[3,2-c]-quinolines from readily available nitrobenzenes and glycols is reported. The process utilizes the carbonyl byproduct of the initial dioxomolybdenum(VI)-catalyzed reduction of nitroaromatics with glycols as a reagent for the imine generation. This method represents the first sustainable domino reaction for the preparation of biologically relevant heterocycles that internally incorporates the waste formed in the first step to the final product.