Synthetic routes of azo derivatives: A brief overview

Preparation of Dinitrogen Trioxide for Organic Synthesis: A Phase Equilibrium Approach

Dinitrogen trioxide (N2O3) is a potent nitrosating agent featured with high reactivity and appealing atom economy. Because of its instability and the entanglement of chemical and phase equilibria, N2O3 has rarely been utilized in organic synthesis as a stock reagent with well-defined composition. In this review, the preparations of pure N2O3 and its concentrated solution (>0.1 M) are discussed from the aspect of phase equilibrium. Understanding the physical and chemical characteristics of N2O3, along with how reaction parameters (temperature, pressure, molar ratio) interact, plays a crucial role in managing the concentration of N2O3 in the liquid phase. This control holds practical significance in achieving quantitative reactions.

Endophytic Aspergillus hiratsukae mediated biosynthesis of silver nanoparticles and their antimicrobial and photocatalytic activities

In the current study, endophytic Aspergillus hiratsukae was used for the biosynthesis of silver nanoparticles (Ag-NPs) for the first time. The characterizations were performed using X ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), and UV-Vis spectroscopy. The obtained results demonstrated the successful formation of crystalline, spherical Ag-NPs with particle diameters ranging from 16 to 31 nm. The FT-IR studied and displayed the various functional groups involved, which played a role in capping and reducing agents for Ag-NPs production. The SEM-EDX revealed that the main constituent of the AS-formed sample was primarily Ag, with a weight percentage of 64.2%. The mycosynthesized Ag-NPs were assessed for antimicrobial as well as photocatalytic activities. The antimicrobial results indicated that the synthesized Ag-NPs possess notable antibacterial efficacy against Staphylococcus aureus, Bacillus subtilis, and Escherichia coli, with minimum inhibitory concentrations (MICs) of Ag-NPs ranging from 62.5 to 250 μg/mL. Moreover, the biosynthesized Ag-NPs demonstrated weak antifungal activity against Aspergillus brasiliensis and Candida albicans, with MICs of 500 and 1,000 μg/mL, respectively. In addition, the mycosynthesized Ag-NPs exhibited photocatalytic activity toward acid black 2 (nigrosine) dye under both light and dark stimulation. Notably, After 300 min exposure to light, the nigrosine dye was degraded by 93%. In contrast, 51% degradation was observed after 300 min in darkness. In conclusion, Ag-NPs were successfully biosynthesized using endophytic A. hiratsukae and also exhibited antimicrobial and photocatalytic activities that can be used in environmental applications.

Emerging trends in the sustainable synthesis of N-N bond bearing organic scaffolds

N-N bond bearing organic frameworks such as azos, hydrazines, indazoles, triazoles and their structural moieties have piqued the interest of organic chemists due to the intrinsic nitrogen electronegativity. Recent methodologies with atom efficacy and a greener approach have overcome the synthetic obstacles of N-N bond construction from N-H. As a result, a wide range of amine oxidation methods have been reported early on. This review's vision emphasizes the emerging methods of N-N bond formation, particularly photo, electro, organo and transition metal free chemical methods.

Rational synthesis, biological screening of azo derivatives of chloro-phenylcarbonyl diazenyl hydroxy dipyrimidines/thioxotetrahydropyrimidines and their metal complexes

Herein, a new series of azo ligands HL-1 (5-(2-chloro-6-(phenylcarbonyl)phenyl)diazenyl)-6-hydroxydihydropyrimidines-2,4dione), HL-2 (5-(2-chloro-6-(phenylcarbonyl)phenyl)diazenyl)-6-hydroxy-2-thioxottetrahydropyrimidin-4one), HL-3 (5-(2,4-dichloro-6-(phenylcarbonyl)phenyl) diazenyl)-6-hydroxydihydropyrimidines-2,4dione), HL-4 (5-(2,4-dichloro-6-(phenylcarbonyl) phenyl)diazenyl)-6-hydroxy-2-thioxotetrahydropyrimidin-4one) and their metal complexes with Cu(II) & Ni(II) were synthesized successfully having excellent yield, in reproducible conditions and for structure elucidation different advance spectroscopic techniques (FTIR, ¹H NMR, ¹³C NMR and Mass Spectrometry) were applied. In FTIR analysis, the absence of peak at 3450-3550 cm ^-1 due to -NH₂ and presence of a new peak of N=N at 1390-1520 cm^-1 confirmed synthesis of the ligands. The ¹H NMR spectra of azo ligands showed singlet peak at 11.5-13.5 ppm (Ar-OH) for hydroxyl group and -NH₂ signals disappearance of anilines at 4-5 ppm also gives strong indication for the synthesis of azo compounds. On complexation two most important peaks (M-O, M-N) appeared in all the metal chelates in the range of 400-600 cm^-1 which were not present in any of the ligands, confirmed the formation of complexes. Molecular ion peaks in mass spectra at 273, 388, 407 and 423 m/z value for ligands as well as for complexes at 803, 835, 871 and 904 m/z also give strong indication that proposed ligands and their metal complexes are produced successfully. Biological screening of the synthesized compounds were also carried out against different bacterial strains (E.coli, S.typhi, and B.subtilis), antifungal (C.albicans, A.niger, and C.glabrata) strains and antioxidant activity. From results it was observed that HL-4 and Cu complexes exhibited maximum inhibition against all bacterial and fungal strains as compared to other ligands and standard drug.

Protocol for microwave-assisted synthesis of unsymmetrical azo dyes

Aromatic azo dyes bear immense commercial significance because of their extensive usage in the textile, paint, and food industries. With growing environmental concerns, developing alternative greener approaches for the synthesis of azo dyes is crucial. Herein, we describe a metal-free, microwave (MW)-assisted protocol for rapid access to a large variety of unsymmetrical azo dyes by coupling nitroarenes and aromatic amines. After MW-assisted coupling, the azo dyes are then isolated by precipitation followed by recrystallization to obtain pure azo dyes. For complete details on the use and execution of this protocol, please refer to Thakuri et al. (2022).¹.

Rational synthesis and characterization of highly water stable MOF@GO composite for efficient removal of mercury (Hg2+) from water

The present study is aimed at adsorptive removal of Mercury (Hg²⁺) using highly functionalized nanomaterials based on Graphene Oxide Zeolitic Imidazolate Framework composite (ZIF-67@GO). Solvothermal methodology was used to synthesize ZIF-67@GO composite. Synthesized compounds were confirmed by FTIR, SEM, PXRD and EDX analysis. The as-prepared ZIF-67@GO was tested as efficient adsorbent for effective removal of Mercury (Hg²⁺) from aquatic environment. The atomic adsorption spectrophotometer was used to monitor the process of adsorption of Hg⁺² on ZIF-67@GO. From the adsorption data, the maximum removal efficiency achieved was 91.1% using 10 mg amount of composite for 50 mL using 20 ppm Mercury (Hg²⁺) solution. Different parameters like pH, contact time, concentration, adsorption kinetics and isotherm were also examined to explore adsorption process. Adsorption data fitted well for Freundlich Model having R² value of 0.9925 than Langmuir Isotherm with R² value of 0.9238. Kinetics were rapid and excellently described via 2nd order model with R² = 0.99946 than 1st order model with R² value of 0.8836. Freundlich and pseudo 2nd order models validated that multilayer chemisorption occurs during adsorption process due to the presence of highly functionalized sites on ZIF-67@GO composite. The synthesized composite material has shown excellent reusability. Thus, water stable ZIF-67@GO composites can efficiently be used for Mercury (Hg²⁺) confiscation from water.

Exploring the Biosorption of Methylene Blue Dye onto Agricultural Products: A Critical Review

Due to their higher specific area and, in most cases, higher adsorption capacity, nanomaterials are noteworthy and attractive adsorbents. Agricultural products that are locally available are the best option for removing methylene blue (MB) dye from aqueous solutions. Because it is self-anionic, FT-IR and SEM investigations of biosorption have confirmed the role of the functional group and its contribution to the formation of pores that bind cationic dye. It is endothermic if the adsorption of MB by an adsorbent is high as the temperature increases; on the other hand, exothermic if it is high as the temperature decreases. A basic medium facilitates adsorption with respect to pH; adsorption is proportional to the initial concentration at a certain level before equilibrium; after equilibrium, adsorption decreases. A pseudo-second-order model applies for certain agricultural products. As per plotted graph for the solid-phase concentration against the liquid-phase concentration, the Langmuir adsorption isotherm model is favored; this model describes a situation in which a number of molecules are adsorbed by an equal number of available surface sites, and there is no interaction between adsorbate molecules once all sites are occupied. In contrast, the Freundlich model depicts non-ideal multi-layer sorption onto heterogeneous surfaces via numerical analysis; with a value of n = 1, the result is a linear isotherm. If the value of n < 1 or n > 1, then it is chemical or physical adsorption, respectively. Based on an EDX analysis, relevant elements are confirmed. BET analysis confirms the surface area. Nanoproducts categorized as agricultural products exhibit the aforementioned tendency. Even though nanoparticles show positive outcomes in terms of higher adsorption, a high specific area for the targeted pollutant is needed in real-world applications. In the relevant sections herein, the behavior of thermodynamic parameters, such as enthalpy, entropy, and Gibbs free energy, are examined. There is some question as to which form of agricultural waste is the most effective adsorption medium. There is no direct answer because every form of agricultural waste has its own distinct chemical and physical characteristics, such as porosity, surface area, and strength.

Headspace Extraction of Chlorobenzenes from Water Using Electrospun Nanofibers Fabricated with Calix[4]arene-Doped Polyurethane-Polysulfone

Chlorobenzenes (CBs) are persistent and potentially have a carcinogenic effect on mammals. Thus, the determination of CBs is essential for human health. Hence, in this study, novel polyurethane−polysulfone/calix[4]arene (PU-PSU/calix[4]arene) nanofibers were synthesized using an electrospinning approach over in-situ coating on a stainless-steel wire. The nanosorbent was comprehensively characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) techniques. The SEM analysis depicted the nanofiber’s unique morphology and size distribution in the range of 50−200 nm. To determine the levels of 1,2,4-trichlorobenzene, 1,2,3-trichlorobenzene, and 1,2,3,4-tetrachlorobenzene in water samples, freshly prepared nanosorbent was employed using headspace-solid phase microextraction (HS-SPME) in combination with gas chromatography micro electron capture detector (GC-µECD). Other calixarenes, such as sulfonated calix[4]arene, p-tert-calixarene, and calix[6]arene were also examined, and among the fabricated sorbents, the PU−PSU/calix[4]arene showed the highest efficiency. The key variables of the procedure, including ionic strength, extraction temperature, extraction duration, and desorption conditions were examined. Under optimal conditions, the LOD (0.1−1.0 pg mL−1), the LDR (0.4−1000 pg mL−1), and the R2 > 0.990 were determined. Additionally, the repeatability from fiber to fiber and the intra-day and inter-day reproducibility were determined to be 1.4−6.0, 4.7−10.1, and 0.9−9.7%, respectively. The nanofiber adsorption capacity was found to be 670−720 pg/g for CBs at an initial concentration of 400 pg mL−1. A satisfactory recovery of 80−106% was attained when the suggested method’s application for detecting chlorobenzenes (CBs) in tap water, river water, sewage water, and industrial water was assessed.

Microwave Assisted Rapid and Sustainable Synthesis of Unsymmetrical Azo Dyes by Coupling of Nitroarenes with Aniline Derivatives

Aromatic azo dyes are of immense commercial importance, and the development of greener routes for their synthesis is imperative due to current environmental concerns. In the present study, a microwave-assisted route has been developed for rapid and convenient synthesis of unsymmetrical azo dyes in a single step. In a metal-catalyst-free approach, an aromatic amine was used as an in situ reductant to affect its direct cross-condensation with nitroarenes to afford a variety of dispersed and water-soluble azo dyes. The electronic and substituent effects were thoroughly understood by placing suitable substituents in both nitroarenes and aniline derivatives in competitive reactions. The microwave (MW) method worked better with aniline or electron-rich aromatic amines to prepare a range of unsymmetrical azo dyes in up to 97% yields within a few minutes. The method worked well in the gram-scale synthesis of commercial dye, solvent yellow 7.

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Microwave-based green synthesis of unsymmetrical azo dyes

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Catalyst-free, rapid synthesis

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Gram-scale synthesis of commercial dyes

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Efficient synthesis of water-soluble dyes