Ultrasound-promoted greener synthesis of 2,4,5-trisubstituted imidazoles catalyzed by Zr(acac)4 under ambient conditions

A simple, efficient and green procedure has been developed for the synthesis of 2,4,5-trisubstituted imidazoles catalyzed by zirconium (IV) acetylacetonate using ultrasonic irradiation. The present methodology offers several advantages such as excellent yields, simple procedure, short reaction times and milder conditions.     

N-Sulfonic acid poly(4-vinylpyridinium) hydrogen sulfate as an efficient and reusable solid acid catalyst for one-pot synthesis of xanthene derivatives in dry media under ultrasound irradiation

N-Sulfonic acid poly(4-vinylpyridinium) hydrogen sulfate catalyzed efficiently the synthesis of xanthene derivatives under ultrasonic irradiation at room temperature, which has prompted various concerns involving cost and environmental persistence. This methodology shows the effect of presence of anion hydrogen sulfate as an important and effective factor on the promotion of the one-pot multi-components and condensation reactions. The catalyst can be recovered by simple filtration and used for several times without a significant loss of catalytic activity.     

The solvent-free synthesis of 1,4-dihydropyridines under ultrasound irradiation without catalyst

The condensation of aldehydes, ethyl acetoacetate and ammonium acetate result 1,4-dihydropyridines in 82–99% yields under ultrasound irradiation without solvent and catalyst at room temperature. Compared with conventional methods, the main advantages of the present procedure are milder conditions, shorter reaction time and higher yields.     

An efficient synthesis of 3-substituted indole derivates under ultrasound irradiation

A solvent-free procedure for the synthesis of 3-substituted indole derivates from indoles and nitroalkenes under ultrasound irradiation is described. Control experiments disclosed besides mechanical effects, namely agitation, sonochemical effects are the main forces to drive the reaction. In the method, 2-chloroethanol was used to prepare a wide variety of 3-substituted indole derivates. This procedure only need equimolar amounts of reaction substrates and can be readily scaled up.     

An efficient and green synthesis of novel benzoxazole under ultrasound irradiation

Ultrasound as green process and an alternative energy source was investigated for the environmentally benign synthesis of novel benzoxazoles from different azo-linked salicylic acid derivatives and 2-amino-4-chlorophenol in short reaction time and high yield. These benzoxazole compounds have been characterized by elemental analysis, FT-IR, ¹H NMR and ¹³C NMR spectroscopy.     

A convenient and efficient protocol for the synthesis of 5-aryl-1,3-diphenylpyrazole catalyzed by hydrochloric acid under ultrasound irradiation

The synthesis of 5-aryl-1,3-diphenylpyrazole via the reactions of 3-aryl-2,3-epoxy-1-phenyl-1-propanone with phenylhydrazine was carried out in 69–99% yields at room temperature under ultrasound irradiation. This method provides several advantages such as operational simplicity, higher yield and environment friendly.     

One-pot three-component Mannich-type reactions using Sulfamic acid catalyst under ultrasound irradiation

Sulfamic acid (NH₂SO₃H, SA) was used as an efficient, inexpensive, non-toxic and recyclable green catalyst for the ultrasound-assisted one-pot Mannich reaction of aldehydes with ketones and amines. This ultrasound protocol has advantages of high yield, mild condition, no environmental pollution, and simple work-up procedures. Most importantly, β-aminocarbonyl compounds with ortho-substituted aromatic amines are obtained in acceptable to good yields by this methodology for the first time.     

An efficient synthesis of pyrido[2,3-d]pyrimidine derivatives and related compounds under ultrasound irradiation without catalyst

A series of pyrido[2,3-d]pyrimidine derivatives and related compounds were synthesized via the condensation reaction of an aldehyde, 2,6-diaminopyrimidine-4(3H)-one and either tetronic acid or 1,3-indanedione under ultrasonic irradiation without catalyst. This protocol has the advantages of higher yields, lower cost and convenient procedure.     

A facile synthesis of deuteroporphyrins derivatives under ultrasound irradiation

A facile, efficient and general method for preparing deuteroporphyrin derivatives by using concentrated H₂SO₄ and alcohol under ultrasound irradiation has been developed. A series of new deuteroporphyrin derivatives bearing different propionic ester groups have been synthesized in good yields starting from readily accessible deuterohemin. The characterization of these compounds confirms the synthetic methodology. Compared with conventional methods, the main advantages of the present procedure are shorter reaction time and higher yields.     

Introduction of poly(4-vinylpyridinium) perchlorate as a new,efficient, and versatile solid acid catalyst for one-pot synthesis of substituted coumarins under ultrasonic irradiation

Poly(4-vinylpyridinium) perchlorate, is a supported, recyclable, eco-benign catalyst for synthesis of substituted coumarins via Pechmann reaction using ultrasound irradiation at room temperature and neat condition in high yields with short reaction times. The catalyst was studied by FT-IR, X-ray diffraction, scanning electron microscope, thermo-gravimetric and energy dispersion X-ray analyses. All the products were extensively characterized by ¹H NMR, FT-IR, MS and melting point analyses. This methodology offers momentous improvements over various options for the synthesis of coumarins with regard to yield of products, simplicity in operation and green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be reused and recovered for several times without loss of activity.     

Scaffold-directed and traceless synthesis of tricyclic quinoxalinone imidazoles under microwave irradiation

Traceless synthesis of 2-aminoimidazoquinoxalinones has been performed on soluble polymer support under open-vessel microwave dielectric heating. The reaction progression is monitored directly by the conventional proton NMR which indicated no release of the substrate from the support. Fmoc-deprotected amino acid polymer conjugates react with 1,5-difluoro-2,4-dinitro benzene to yield polymer bound dinitro fluoro amines, which are further substituted by various primary amines to yield PEG-immobilized dinitrodiamines. Simultaneous reduction of aromatic meta-dinitro group leads to the traceless release of 2-quinoxalinones, followed by N-hetero cyclization with various isothiocyanates in the presence of mercury(II)chloride to furnish 2-aminoimidazoquinolinone rings with three points of diversity at rapid pace.     

Improved synthesis of chalcones under ultrasound irradiation

Claisen-Schmidt condensation of acetophenone with aromatic aldehydes catalyzed by pulverized KOH and KF-Al2O3 results chalcones in 52-97% and 83-98% yields respectively in alcoholic solvent under ultrasound irradiation.     

Improved synthesis of chalconoid-like compounds under ultrasound irradiation

Claisen–Schmidt condensation of various substituted acetophenones with cinnamaldehyde catalyzed by KF–Al₂O₃ results chalconoid-like compounds, (2E,4E)-1,5-diarylpenta-2,4-dien-1-ones, in 67–92% yields in 5–60 min under ultrasound irradiation.     

Destruction of polylactic acid microcapsules under ultrasound irradiation

Hollow microcapsules have been considered for potential applications as drug or gene carriers. This paper describes an investigation into the mechanical properties of microcapsules with a biocompatible polylactic acid (PLA) shell that can be destroyed using ultrasound irradiation. The microcapsules had a radius of 1 to 25 μm and a shell thickness of 100 nm to 3 μm, and their response to ultrasound pulses with a center frequency of 700 kHz to 2 MHz was investigated. It was found that approximately 50% of capsules with a radius of 20 μm were destroyed using pulses with a pressure amplitude of 50 kPa and a frequency of 700 kHz, which is close to the resonance frequency of the capsules.     

One-pot synthesis of benzylacetamide from oxime under ultrasound irradiation

One-pot synthesis of benzylacetamide from oxime can be carried out in 80–95% yield at 35–40 °C under ultrasound irradiation. This method provided several advantages such as simple work-up procedure, shorter reaction time and higher yield.     

A novel sodium iodide and ammonium molybdate co-catalytic system for the efficient synthesis of 2-benzimidazoles using hydrogen peroxide under ultrasound irradiation

The reaction of aldehydes and o-phenylenediamine for the preparation of 2-benzimidazoles has been studied using hydrogen peroxide as an oxidant under ultrasound irradiation at room temperature in this paper. The combination of substoichiometric sodium iodide and ammonium molybdate as co-catalysts, together with using small amounts of hydrogen peroxide, makes this transformation very efficient and attractive under ultrasound. Thus, a mild, green and efficient method is established to carry out this reaction in high yield.     

Poly(4-vinylpyridine) supported acidic ionic liquid: A novel solid catalyst for the efficient synthesis of 2,3-dihydroquinazolin-4(1H)-ones under ultrasonic irradiation

A novel poly(4-vinylpyridine) supported acidic ionic liquid catalyst was synthesized by the reaction of 4-vinylpyridine with 1,3-propanesultone, followed by the polymerization and the addition of the heteropolyacid. Due to the combination of polymer features and ionic liquid, it acted as a heterogeneous catalyst to effectively catalyze the cyclocondensation reaction of anthranilamide with aldehydes under ultrasonic irradiation and afforded the corresponding 2,3-dihydro-4(1H)-quinazolinones compounds in good to excellent yields. In addition, the catalyst could be easily recovered by the filtration and reused six times without significant loss of catalytic activity. More importantly, the use of ultrasonic irradiation can obviously accelerate the reaction.     

Low intensity-ultrasonic irradiation for highly efficient,eco-friendly and fast synthesis of graphene oxide

High quality graphene oxide (GO) with low layer number (less than five layers) and large inter-layer space was produced via a new and efficient method using environmentally friendly, fast and economic ultrasonic radiation. The ultrasonic method neither generated any toxic gas nor required any NaNO₃, which have been the main drawbacks of the Hummers methods. The major obstacles of the recently reported improved Hummers method for GO synthesis, such as high reaction temperature (50 °C) and long reaction time (12 h), were successfully solved using a low intensity-ultrasonic bath for 45 min at 30 °C, which significantly reduced the reaction time and energy consumption for GO synthesis. Furthermore, ultrasonic GO exhibited higher surface area, higher crystallinity and higher oxidation efficiency with many hydrophilic groups, fewer sheets with higher spaces between them, a higher sp³/sp² ratio, and more uniform size distribution than classically prepared GO. Therefore, the new ultrasonic method could be applicable for the sustainable and large-scale production of GO. The production yield of the ultrasonic-assisted GO was 1.25-fold greater than the GO synthesized with the improved Hummers method. Furthermore, the required production cost based on total energy consumption for ultrasonic GO was only 6.5% of that for classical GO.     

An efficient and practical synthesis of mandelic acid by combination of complex phase transfer catalyst and ultrasonic irradiation

Mandelic acid was synthesized from benzaldehyde with chloroform in a 81% yield at 60 degrees C for 2 h by using triethylbenzylammonium chloride (TEBA) and poly(ethylene glycol)-800 (PEG-800) as a complex phase transfer catalyst under ultrasonic irradiation. The main advantages of this present method are that the reaction time is much shorter and the yield is higher than those of the classical method. p-Methoxymandelic acid was also obtained in a 84% yield under the same reaction conditions.