An efficient and green synthesis of novel benzoxazole under ultrasound irradiation

Co3O4@chitosan/La2O3 nanocomposites as innovative, powerful, and recyclable nanocatalysts for sonochemical treatment of benzyl alcohols to obtain the corresponding benzaldehyde derivatives

Ultrasonic (US) irradiation (100 W, 40 kHz) reactions, used as a safe and green technique, are often more efficient than traditional protocols. This leads us to introduce, for the first time, an efficient nanocatalyst and immobilization of La₂O₃ nanoparticles on Co₃O₄ nanoparticles for the selective oxidation of benzyl alcohol to the corresponding benzaldehyde at room temperature. The structural and morphological characteristics of the nanocatalysts were determined by FT-IR, XRD, FE-SEM, EDX, and VSM. The catalytic performance of the Co₃O₄@Cs/La₂O₃ composites used as heterogeneous nanocatalysts was investigated in the selective oxidation of benzylic alcohols to their corresponding benzaldehydes. Also, the performance of the oxidation parameters, including H₂O₂ concentration, time, effect of various solvents, and nanocatalyst dosage was checked. Significant benefits of this method can be named by using a non-toxic solvent, easy product isolation, excellent recoverability, low time of reaction, high yield, and ultrasound irradiation. Finally, a possible mechanism was proposed to show the nanocatalytic process.

Ultrasound-assisted transition-metal-free catalysis: a sustainable route towards the synthesis of bioactive heterocycles

Heterocycles of synthetic and natural origin are a well-established class of compounds representing a broad range of organic molecules that constitute over 60% of drugs and agrochemicals in the market or research pipeline. Considering the vast abundance of these structural motifs, the development of chemical processes providing easy access to novel complex target molecules by introducing environmentally benign conditions with the main focus on improving the cost-effectiveness of the chemical transformation is highly demanding and challenging. Accordingly, sonochemistry appears to be an excellent alternative and a highly feasible environmentally benign energy input that has recently received considerable and steadily increasing interest in organic synthesis. However, the involvement of transition-metal-catalyst(s) in a chemical process often triggers an unintended impact on the greenness or sustainability of the transformation. Consequently, enormous efforts have been devoted to developing metal-free routes for assembling various heterocycles of medicinal interest, particularly under ultrasound irradiation. The present review article aims to demonstrate a brief overview of the current progress accomplished in the ultrasound-assisted synthesis of pharmaceutically relevant diverse heterocycles using transition-metal-free catalysis.

Distinguished performance of biogenically synthesized reduced-graphene-oxide-based mesoporous Au–Cu2O/RGO ternary nanocomposites for sonocatalytic reduction of nitrophenols in water

Au-Cu2O supported on reduced graphene oxide was synthesised employing a novel one pot greener approach using sugarcane bagasse waste and Fehling’s solution. It was used for catalytic reduction of nitrophenols under ultrasonic irradiation in water.

Green synthesis of novel 5-amino-bispyrazole-4-carbonitriles using a recyclable Fe3O4@SiO2@vanillin@thioglycolic acid nano-catalyst

Bis(thioglycolic acid)-vanillin (2,2'-(((4-hydroxy-3-methoxyphenyl)methylene)bis(sulfanediyl))diacetic acid)-functionalized silica-coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2@vanillin@thioglycolic acid MNPs) were synthesized and characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis/differential thermogravimetry (TGA-DTG), X-ray powder diffraction (XRD), X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), zeta potential measurements and Fourier transform infrared spectroscopy (FT-IR). The ensuing MNPs offer an environmentally friendly procedure for the synthesis of novel 5-amino-pyrazole-4-carbonitriles via a three-component mechanochemical reaction of synthesized azo-linked aldehydes or synthesized pyrazolecarbaldehydes, malononitrile, and phenylhydrazine or p-tolylhydrazine adhering to the green chemistry principles; products were generated expeditiously in high yields. The catalyst could be quickly recovered and reused for six cycles with almost consistent activity. The structures of the synthesized 5-amino-pyrazole-4-carbonitrile compounds were confirmed by 1H NMR, 13C NMR, and FTIR spectra and elemental analyses. This new procedure has notable advantages such as operational simplicity, excellent yields, short reaction time, easy work-up, eco-friendliness and nontoxic catalyst. Also the catalyst can be easily recovered by an external magnetic field and reused for six consecutive reaction cycles without significant loss of activity.

Synthesis of Novel Azo-Linked 5-Amino-Pyrazole-4-Carbonitrile Derivatives Using Tannic Acid-Functionalized Silica-Coated Fe3O4 Nanoparticles as a Novel, Green, and Magnetically Separable Catalyst

Tannic acid-linked silica-coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂@Tannic acid) were prepared and characterized by transmission electron microscope (TEM), field emission scanning electron microscope (FE-SEM), X-ray powder diffraction (XRD), X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), and Fourier transform infrared (FT-IR) spectroscopy. Fe₃O₄@SiO₂@Tannic acid supplies an environmentally friendly procedure for the synthesis of some novel 5-amino-pyrazole-4-carbonitriles through the three-component mechanochemical reactions of synthetized azo-linked aldehydes, malononitrile, and phenylhydrazine or p-tolylhydrazine. These compounds were produced in high yields and at short reaction times. The catalyst could be easily recovered and reused for six cycles with almost consistent activity. The structures of the synthesized 5-amino-pyrazole-4-carbonitrile compounds were confirmed by ¹H NMR, ¹³C NMR, and FTIR spectra, and elemental analyses.

Organocatalyzed Heterocyclic Transformations In Green Media: A Review

Background:

Since the discovery of metal-free catalysts or organocatalysts about twenty years ago, a number of small molecules with different structures have been used to accelerate organic transformations. With the development of environmental awareness, to obtain highly efficient scaffolds, scientists have directed their studies towards synthetic methodologies that minimize or preferably eliminate the formation of waste, avoid toxic solvents and reagents and use renewable starting materials as far as possible.

Methods:

In this connection, the organocatalytic reactions providing efficiency and selectivity for most of the transformations have become an endless topic in organic chemistry since several advantages from both practical and environmental standpoints. Organocatalysts contributing to the transformation of reactants into products with the least possible waste production, have been serving the concept of green chemistry.

Results and Conclusion:

Organocatalysts have been classified based on their binding capacity to the substrate with covalent or noncovalent interactions involving hydrogen bonding and electrostatic interaction. Diverse types of small organic compounds including proline and its derivatives, phase-transfer catalysts, (thio)urease, phosphoric acids, sulfones, N-oxides, guanidines, cinchona derivatives, aminoindanol, and amino acids have been utilized as hydrogen bonding organocatalysts in different chemical transformations.

Grinding Synthesis of Pyrazolyl-Bis Coumarinyl Methanes Using Potassium 2-Oxoimidazolidine-1,3-diide

AIM AND OBJECTIVE

Potassium 2-oxoimidazolidine-1,3-diide (POImD) as a novel and reusable catalyst was used for the synthesis of pyrazolyl-bis coumarinyl methanes by a nucleophilic addition reaction of synthetized pyrazolecarbaldehyde and two equivalents of 4-hydroxycoumarin under grinding. The catalyst can be reused and recovered several times without loss of activity. This method provides several advantages such as eco-friendliness, simple work-up and shorter reaction time as well as excellent yields. All of the synthesized compounds were characterized by IR, 1H and 13C NMR spectroscopy and elemental analyses.

MATERIAL AND METHOD

Synthetized pyrazole carbaldehyde 1a (1 mmol), 4-hydroxycoumarin 2 (2 mmol), 1 mmol of POImD and 10mL of H2O were ground in a mortar by a pestle for 30-90 minutes. After the completion of the reaction, as monitored by TLC on silica gel using ethyl acetate/n-hexane (1:2), the mixture was allowed to cool to room temperature. After completion of the reaction, we extracted the product with CH2Cl2/H2O. This was followed by separation of phases, evaporation of the organic phase and recrystallization of the residue with 50 mL of ethanol/H2O (1:1). The pure product was then obtained in 87 to 96% yield. The aqueous phase was concentrated under reduced pressure to recover the catalyst for subsequent use.

RESULTS

To continue our ongoing studies to synthesize heterocyclic and pharmaceutical compounds by mild, facile and efficient protocols, herein we wish to report our experimental results on the synthesis of pyrazolylbis coumarinyl methanes, using various synthetized pyrazole carbaldehydes and 4-hydroxycoumarin in the presence of POImD in aqueous media at room temperature.

CONCLUSION

Finally, we developed an efficient, fast and convenient procedure for the three-component synthesis of pyrazolyl-bis coumarinyl methanes through the reaction of pyrazole carbaldehydes and 4- hydroxycoumarin, using POImD as a novel and reusable catalyst. The remarkable advantage offered by this method is that the catalyst is non-toxic, inexpensive, easy to handle and reusable. A short reaction time, simple work-up procedure, high yields of product with better purity and the green aspect by avoiding a hazardous solvent and a toxic catalyst are the other advantages. To the best of our knowledge, this is the first report on the synthesis of pyrazolyl-bis coumarinylmethane derivatives using potassium 2-oxoimidazolidine-1,3-diide (POImD).

Studied on sonocatalytic degradation of Rhodamine B in aqueous solution

This paper describes experimental results of degradation of Rhodamine B (RB) by vortex scattering ultrasound in aqueous solution. Vortices are produced by a high-speed agitator. The effects of different factors on the degradation of RB solution were studied, such as different reaction container, the initial concentration of RB, stirring speed and ultrasonic frequencies. Ultraviolet-visible spectrophotometer (UV) was used to measure the absorbance value of RB to assess degradation rate. The optimal experimental condition was three-necked bottle, stirring speed of 700 r/min, initial concentration of 10 mg/L and ultrasonic frequency of 40 kHz. The optimal degradation rate of RB can reach 98% within one hour. The combination of ultrasonic irradiation and mechanical stirring was discovered that can degrade the RB efficiently in aqueous solution. The investigation of mechanism demonstrates that the cavitation bubbles produced by agitation play a major role in promoting degradation. COMSOL Multiphysics (Version 5.3a) software was used to simulate this process. And the method of combination of ultrasonic irradiation and mechanical stirring has also been shown to be effective in degrading methylene blue, bromophenol blue and Congo red. So the combination of ultrasonic irradiation and mechanical stirring can be used as an option for treating organic wastewater in the future. This study established a new way to degrade other organic pollutants.

Synthesis of Benzoxazoles, Benzimidazoles, and Benzothiazoles Using a Brønsted Acidic Ionic Liquid Gel as an Efficient Heterogeneous Catalyst under a Solvent-Free Condition

Herein, we introduce a reusable Brønsted acidic ionic liquid gel (BAIL gel) obtained by treating 1-methyl-3-(4-sulfobutyl)-1H-imidazolium hydrogen sulfate with tetraethyl orthosilicate (TEOS). The grafting of the Brønsted acidic ionic liquid to the surface of TEOS has increased the catalytic activity of the material and also simplified catalyst recovery from the reaction mixture. This reaction has a wide substrate scope, and the BAIL gel represents a new catalyst for the synthesis of benzoxazoles, benzimidazoles, and benzothiazoles. The method shows attractive characteristics such as high yields, recyclable catalyst, and work-up simplicity. More importantly, no additional additives or volatile organic solvent and inert atmosphere are required for the reaction, and the BAIL gel has shown a great promise for industrial applications. To the best of our knowledge, the synthesis of benzoxazoles, benzimidazoles, and benzothiazoles using a recyclable heterogeneous ionic liquid gel was not previously reported in the literature.

Sonocatalytic degradation of methyl orange in aqueous solution using Fe-doped TiO2 nanoparticles under mechanical agitation

In the present study, the Fe-doped TiO2 modified nanoparticles was successfully synthesized by the combination of the sol-gel method and heat treatment, and the degradation of methyl orange was tested by the combination method of ultrasonic radiation and mechanical agitation. The effects of different factors on the degradation of methyl orange (MO) solution were studied, such as ultrasonic irradiation time, the ultrasonic frequency, the added amount of catalyst, the initial pH value, the initial concentration of methyl orange, and revolutions per minute. The optimal experimental conditions for sonocatalytic degradation of the MO obtained were: ultrasonic irradiation time = 60 min, pH value = 3.0 and revolutions per minute = 500 rpm. By means of response surface analysis, the best fitting conditions were as follows: ultrasonic frequency = 36.02 kHz, added amount of catalyst = 490.50 mg/L, the initial concentration of methyl orange = 9.22 mg/L, and the optimum condition was close to the experimental data by response surface method. Under optimal conditions, the sonocatalytic degradation of MO was 99%. The degradation of MO showed that the combination of Fe-doped modified TiO2 nanoparticles, mechanical agitation and ultrasonic irradiation was discovered that can degrade methyl orange effectively in aqueous solution.

One-pot sonochemical synthesis of magnetite@reduced graphene oxide nanocomposite for high performance Li ion storage

In this research, we introduce a one-pot sonochemical method for the fabrication of magnetite@reduced graphene oxide (Fe₃O₄@rGO) nanocomposite as anode material for Li-ion batteries. Fe₃O₄@rGO is synthesized under ultrasonic irradiations by using iron (II) salt and GO as raw materials. An in-situ oxidation-reduction occurs between GO and Fe²⁺ during the ultrasonic chemical reaction process. Fe₃O₄ particles with the size of ∼20 nm are uniformly deposited on the surface of rGO nanosheets. The electrochemical activity of Fe₃O₄@rGO is systematically evaluated as an anode material in Li-ion battery. Li-ion cells using Fe₃O₄@rGO as electrode deliver high discharge and charge capacities of 1433.6 and 907.8 mAh g^-1 in the initial cycle at 200 mA g^-1. Even performed at 500 and 5000 mA g^-1, it is able to deliver reversible capacities of 846.4 and 355.6 mAh g^-1, respectively, demonstrating outstanding Li-ion storage performance. This research presents a straightforward and efficient method for the fabrication of Fe₃O₄@rGO, which holds great potential in synthesis of other metal oxides on graphene sheets.

Synthesis and characterization of amino glucose-functionalized silica-coated NiFe2O4 nanoparticles: a heterogeneous, new and magnetically separable catalyst for the solvent-free synthesis of pyrano[3,2-c]chromen-5(4H)-ones

A novel, efficient and one-pot multi-component procedure for the synthesis of simple pyrano[3,2-c]chromen-5(4H)-ones or pyrazolyl pyrano[3,2-c]chromen-5(4H)-ones via reaction of aryl aldehydes, acetophenones and 4-hydroxycoumarin promoted by amino glucose-functionalized silica-coated NiFe2O4 nanoparticles under solvent-free conditions without using any other harmful organic reagents was reported. The structure of this nanoparticle was characterized by transmission electron microscopies, X-ray diffraction and Fourier transform infrared spectroscopies. The catalyst could easily be separated from the reaction mixture by using an external magnetic field and it was reusable. The high purity of the desired products, eco-friendliness, short reaction time and easy workup procedure can be mentioned as the other advantages of this method.

Ultrasonic impregnation of MnO2/CeO2 and its application in catalytic sono-degradation of methyl orange

MnO₂/CeO₂ catalyst was prepared by ultrasonic impregnation method. The traditional and stirring impregnation methods were used as control. Results showed that ultrasonic impregnation was the best synthesis method. The impregnation time was shortened from 120 min (traditional method) to 20 min, the specific surface area of catalyst was three times larger, and the catalytic activity of catalyst was also the highest. Furthermore, MnO₂ had crystalline structure and distributed uniformly on the support, CeO₂. The preparing conditions were further examined and the optimal conditions were found to be: 20 min of ultrasonic impregnation, 4.3 mol/L of manganese nitrate concentration and 450 °C of calcination temperature. The so prepared catalyst removed 94% of methyl orange in 30 min with a dosage of 0.5 g/L. The efficiency was 77.7% and 85.9% for traditional and stirring impregnation method under the same experimental conditions. The reaction process involved two stages: adsorption-dominated and degradation-dominated stages. The reaction rate constant of adsorption-dominated stage had little difference. However, compared with traditional impregnation, the reaction rate constant of degradation-dominated stage improved from 0.01 to 0.14 min^-1 by ultrasonic impregnation. Mechanism analysis showed that the activity of ultrasonic impregnation MnO₂/CeO₂ was improved by the effects of acoustic cavitation and ultrasound oscillation on solid-liquid transport and distribution status.

Synthesis and antimicrobial activity of pyrimidinyl 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazoles

A new class of methylthio linked pyrimidinyl 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazoles were prepared under conventional and ultrasound irradiation methods. All the compounds were obtained in higher yields and in shorter reaction times in ultrasound irradiation method when compared with the conventional method. The title compounds were tested for antimicrobial activity. The compounds 12c and 12f exhibited promising antibacterial activity against P. aeruginosa whereas the compounds 13c and 13f showed pronounced antifungal activity against A. niger.

Green synthesis of novel 2-pyrazolyl-1,3-thiazolidine-4-ones using 2-oxoimidazolidine-1,3-disulfonic acid

2-Oxoimidazolidine-1,3-disulfonic acid (OImDSA) is a recoverable catalyst for the synthesis of 1,3-thiazolidine-4-ones at room temperature in a one-pot procedure without using any organic solvents. Moreover, the catalyst can be easily recovered and recycled for five runs without significant loss of catalytic activity. The structures of the synthesized 1,3-thiazolidine-4-one compounds were confirmed by

One-pot synthesis of 2-hydrazonyl-4-phenylthiazoles via [PDBMDIm]Br-catalyzed reaction under solvent-free conditions

A clean and environmentally benign route for the preparation of substituted thiazoles