Microwave Activation Conditions Research Articles

Catalysis of the Abramov Reaction under Conditions of Microwave Activation

Two series of α-hydroxyphosphonate synthesis according to the Abramov reaction are conducted under conditions of microwave activation. Acidic and basic catalysts are used along with 4-bromobenzaldehyde and 3-methoxy-4-hydroxybenzaldehyde. O,O-Diethylphosphite is used as a phosphorylating agent. The conversion of the reaction products is monitored via NMR spectroscopy. The optimum conditions for the synthesis of α-hydroxyphosphonates are selected. The crystal structure of reaction product O,O‑diethyl((4-bromophenyl(hydroxy)methyl)phosphonate 2, which crystallizes in the space group P21/n and is stabilized by multiple C–H⋅⋅⋅O and C–H⋅⋅⋅π interactions, is described for the first time.

Catalysis of the Abramov Reaction under Conditions of Microwave Activation

Catalysis of the Abramov Reaction under Conditions of Microwave Activation

Recent Studies on the Application of Microwave-Assisted Method for the Preparation of Heterogeneous Catalysts and Catalytic Hydrogenation Processes.

Currently, microwave radiation is widely used in various chemical processes in order to intensify them and carry out processes within the framework of "green" chemistry approaches. In the last 10 years, there has been a significant increase in the number of scientific publications on the application of microwaves in catalytic reactions and synthesis of nanomaterials. It is known that heterogeneous catalysts obtained under microwave activation conditions have many advantages, such as improved catalytic characteristics and stability, and the synthesis of nanomaterials is accelerated several times compared to traditional methods used to produce catalysts. The present review article is to summarize the results of modern research on the use of microwave radiation for the synthesis of heterogeneous catalytic nanomaterials and discusses the prospects for research in the field of microwave-induced liquid-phase heterogeneous catalysis in hydrogenation.

Hydroamination of Phenylacetylene on Gold-Containing Catalytic Systems Supported on Substrates Modified with Ionic Liquids under Conditions of Microwave Activation

It is established that catalytic systems based on gold nanoparticles stabilized in ionic liquids and supported on an MCM-41–type mesoporous silica show a high activity and selectivity in hydroamination of phenylacetylene with aniline, obeying Markovnikov’s rule. It is shown that the activity of the synthesized gold-containing systems grows substantially under conditions of microwave activation, which also shortens the time required to achieve full conversion.

Synthesis of 2,7-dibromo-9H-carbazole and its N-alkylation under microwave activation conditions in a flow-type microwave reactor

One of the most popular building blocks for producing organic semiconductors is 2,7-dibromo-9H-carbazole and its derivatives. Building blocks based on 9H-carbazole are among the most expensive building blocks. The article presents new, highly effective, and “green” methods for the synthesis of 2,7-dibromo-9H-carbazole and its derivatives under microwave irradiation. The use of a flow-type microwave reactor significantly reduced the synthesis time. The methods described differ in efficiency, simplicity, performance, and a significant reduction in time compared to classical methods. The research was conducted in accordance with the principles of green chemistry.

Synthesis of hydrazone derivatives of isonicotinic acid under microwave activation conditions

In the article the results of studying the reaction of the interaction of isonicotinic acid hydrazide with various derivatives of aromatic aldehydes under conditions of microwave activation in an alcohol medium were described. The results of studying the dependences of the hydrazone yield on the duration of the activation time at various microwave irradiation powers in comparison with the classical method have been presented. It was found that the main factors affecting the nature of the synthesis and the yields of the target products were the power and time of microwave activation, as well as the structural features of the reactants. For all studied reactions, the optimal conditions for obtaining the target product have been shown. As a result of a comparative analysis of the results obtained for the synthesis of new isonicotinic hydrazones, it was determined that the use of microwave irradiation contributed to an increase in the yield of the product and a decrease in the reaction time by 3-4 times than according to traditional technology. The authenticity of each product is unambiguously proved by comparing the melting point, as well as by analyzing the physico-chemical characteristics with previously synthesized hydrazone derivatives of isonicotinic acid obtained by classical synthesis methods. The structure of all synthesized compounds was studied by H-1 and C-13 NMR spectroscopy, as well as data from two-dimensional COSY (H-1-H-1) spectra and HMQC (H-1-C-13). The developed microwave method for the synthesis of hydrazone derivatives of isonicotinic acid complies with the principles of the concept of Green Chemistry.

Microwave Activation of Reaction between 1,3,5-Trisubstituted Pyrazole-4-carbaldehydes and Sterically Hindered Aminoalcohols

Structure of products of reaction between 1,3,5-trisubstituted pyrazole-4-carbaldehydes and 2-aminoalkan-1-oles is determined by the structure of the alkyl chain of aminoalcohol. The reaction with 2-aminobutan-1-ol proceeds for 2 h in conditions of microwave activation at 150°C with the formation of 2-hydroxyalkylimines of pyrazole-4-carbaldehyde. At reaction of 1,3,5-trisubstituted pyrazole-4-carbaldehydes with 2-amino-2-methylpropan-1-ol mixtures form of the corresponding 2-hydroxyalkylimines and pyrazol-4-yl-1,3-oxazolidines in ratios 66 : 33–80 : 20. Heating of 2-hydroxyalkylimines of pyrazole-4-carbaldehyde in the presence of dehydrating agents, in particular, trimethylchlorosilane, does not result in 1,3-oxazolidines.

SYNTHESIS OF LAPPACONITINE N -OXIDE UNDER THE CONDITIONS OF MICROWAVE ACTIVATION

Lappaconitine N-oxide was obtained in high yield via oxidation of lappaconitine with Oxone® in H 2 O–MeCN media under the conditions of microwave activation. Authors: Natalia A. Pankrushina*, Kymbat B. Rakhmetali

Michael addition to unprotected 3-(2-nitrovinyl)indoles under the conditions of microwave synthesis

A novel highly efficient preparative method for the synthesis of substituted indoles using conjugate addition of nucleophiles to 3-(2-nitrovinyl)indoles has been developed. The addition of nucleophiles generated in the presence of a base from CH acids was investigated. The studied reactions proceed quickly and smoothly under the conditions of microwave activation and do not require protection of the indole nitrogen atom.

Synthesis of lappaconitine N-oxide under microwave activation

Lappaconitine N-oxide was obtained in high yield via oxidation of lappaconitine with Oxone® in H2O–MeCN media under the conditions of microwave activation.

Microwave-assisted synthesis of mesoporous metal-organic framework NH2—MIL-101(Al)

The possibility of formation of the mixed matrix membranes NH2—MIL-101(Al) under the conditions of microwave activation of the reaction mixture at atmospheric pressure is studied. Microwave irradiation affects the morphology and crystallite size and significantly shortens the synthesis time (from tens of hours to 10—30 min). The obtained samples of NH2—MIL-101(Al) with a crystallite size of 100 nm were used as nanofillers for polymer matrix based on the PIM-1 polymer with intrinsic microporosity for the preparation of hybrid membrane materials. Gas permeability for a series of gases was measured on the synthesized membranes.

Preparation of Pinewood- and Wheat Straw-based Activated Carbon via a Microwave-assisted Potassium Hydroxide Treatment and an Analysis of the Effects of the Microwave Activation Conditions

This study explored the effect of activated carbon preparation conditions on their adsorption performance. Pinewood and wheat straw were used as source materials to prepare activated carbon via a fast activation process using KOH and microwave heating. The iodine numbers and carbon yields were determined to evaluate the adsorption properties of the activated carbon. The effects of various KOH/char mass ratios, particle sizes, humidity levels, and microwave heating times on the physical characteristics of the activated carbon were investigated. The iodine number and yield and SEM images were used to characterize the activated carbon. Small particle sizes, the presence of humidity in the purge gas, and high KOH/char ratios resulted in higher iodine numbers. The best activated carbons were obtained using a KOH/char ratio of 3.0, a microwave power of 600 W, a radiation time of 30 min, and a particle size of 0.1 to 0.42 mm in a humid environment; these carbons showed iodine numbers of 2208 mg/g (pinewood activated carbon) and 1420 mg/g (wheat straw activated carbon), with carbon yields of 73% and 52%, respectively. Longer microwave heating times increased the iodine number. The iodine numbers and yields of the pinewood activated carbons were much higher than those of their wheat straw counterparts.

ChemInform Abstract: Copper‐Catalyzed Arylation of Tetrazole‐5‐thiones upon Convection Heating and Microwave Activation Conditions.

AbstractCompared to convection heating, microwave activation increases product yields at the same reaction time and simplifies product isolation due to reduced for formation.

Effects of microwave activation conditions on the properties of activated oil sands coke

Delayed and fluid oil sands cokes were used to prepare activated carbon through a fast activation process that uses microwave heating and KOH as activation agent. Activation parameters such as particle size, humidity of the purge gas, KOH to coke ratio, and microwave heating time were studied for their impact on the quality of the activated cokes obtained. The iodine number, specific surface area, scanning electron microscopic images, elemental analysis and X-ray photoelectron spectroscopy were used to characterize the activated coke obtained. Small particle size, presence of humidity in the purge gas, and high KOH/coke ratio provided higher iodine number and BET surface area. Longer microwave heating time increased the iodine number and surface area of the activated coke, but not monotonically. The differences in the properties of the activated delayed and fluid cokes are related to the structural differences and volatile content of the raw cokes.

Copper-catalyzed arylation of tetrazole-5-thiones upon convection heating and microwave activation conditions

The arylation of 1-phenyltetrazole-5-thione using a series of iodobenzene derivatives in the presence of cuprous chloride and a ligand such as ethylenediamine. It was shown that the use of microwave activation permitted shortening of the reaction time, increasing yields and simplification of the reaction products isolation.

Synthesis, crystal structures, and properties of 5-(het)aryl-3-cyano-1-ethyl-2(1H)-pyrazinones

A simple method for the synthesis of 5-(het)aryl-3-cyano-1-ethyl-2(1H)-pyrazinones was proposed. The method is based on the hydrolysis of the corresponding 2,3-dicyanopyrazinium salts. The spectral properties of pyrazinones were studied and their crystallographic investigation was carried out. The possibility of introduction of 5-(het)aryl-3-cyano-1-ethyl-2(1H)-pyrazinones into the [2+4] cycloaddition under the microwave activation conditions was shown.

Tetrazoles: LVI. Synthesis of 5-substituted tetrazoles under microwave activation in the presence of heterogeneous catalyst (zinc oxide)

Reactions of aromatic and heteroaromatic nitriles with sodium azide in the presence of zinc oxide under the conditions of microwave activation provide 5-aryl(hetaryl)tetrazoles in high yields.

Co(salen)/SBA-15 catalysed oxidation of a β-O-4 phenolic dimer under microwave irradiation

The microwave-assisted oxidative degradation of a lignin model phenolic dimer [1-(4-hydroxy-3-methoxyphenoxy)-2-(2-methoxyphenoxy)-propane-1,3-diol, 1] catalysed by Co(salen)/SBA-15 is reported. The investigated model compound 1 was prepared through a multistep synthesis and characterized by 1H,13C NMR, and GC–MS studies. The catalyst was prepared by immobilizing [N,N′-bis(salicylidene)ethane-1,2-diaminato]Cobalt(II), Co(salen) complex onto the periodic mesopore channels of siliceous SBA-15. The activity of the Co(salen)/SBA-15 was investigated in the oxidation of 1 in the presence of hydrogen peroxide as oxidant, both under microwave irradiation and conventional heating. The phenolic dimer was selectively oxidized to 2-methoxy phenol with very high TON under microwave activation conditions. Comparatively, reactions run under conventional heating led to oligomerisation of the dimer and resulted in a mixture of products.

ChemInform Abstract: A Mild and Convenient One‐Pot Two‐Step Synthesis of Hydroxyiminodihydrobenzofurans Mediated by Silica Gel under Microwave Activation Conditions.

AbstractCyclic 1,3‐dicarbonyl compounds (I) react with various nitroolefins to furnish the title products exclusively or predominantly as (E)‐isomers.

A mild and convenient one-pot two-step synthesis of hydroxy- iminodihydrobenzofurans mediated by silica gel under microwave activation conditions

A convenient one-pot two-step procedure for the synthesis of hydroxyiminodihydrobenzofurans assisted by microwave irradiation in presence of silica gel is described herein. Cyclic 1,3-dicarbonyl compounds reacted smoothly with various nitroolefins to furnish hydroxyiminodihydrobenzofuran derivatives as the mixture of E and Z isomers. Clean reaction conditions, no work-up procedure, easy isolation and good yields of the products are the salient features of the methodology.