Microwave Conditions Research Articles

Microwave-Accelerated Facile Synthesis of pyrano[2,3-d]pyrimidine Derivatives via one-pot Strategy Executed by Agro-Waste Extract as a Greener Solvent Media

background: A variety of methods have been reported for the synthesis of pyrano[2,3- d]pyrimidines in the literature with some limitations, and generally used expensive catalysts, harmful solvent and prolonged reaction time. This paper describes an efficient and rapid multicomponent synthesis of pyrano[2,3-d]pyrimidine through condensation of aromatic aldehyde, malononitrile and barbituric acid catalysed by agro-waste solvent catalyst under microwave irradiation. The present method provides several added advantages such as being environmentally friendly, simple work-up, inexpensive, and shorter reaction time affording excellent yields. The synthesized compounds were confirmed by various spectroscopic analyses such as FT-IR, 1H- &13C-NMR and mass spectrometry. Objective: Develop an eco-friendly method for the synthesis of pyrano[2,3-d]pyrimidine derivatives. Methods: We have selected Water Extract of Lemon Fruit Shell ash extract solvent as a greener homogenous organo catalysts, and reaction is accelerated by microwave irradiation for the inexpensive synthesis of pyrano[2,3-d]pyrimidine derivatives. Results: The pyrano[2,3-d]pyrimidine derivatives are prepared using an agro-waste-based catalyst, which avoids the use of the external base, additives and solvent in multi-component reactions. Further, the rate of the reaction is accelerated by custom-made microwave irradiation. The use of microwave irradiation showed many advantages over conventional methods such as reaction required less time, more yield and fewer by-products. Further, the custom-made microwave oven has the advantage of no spillage of any organic reagent or solvent to the microwave oven walls, because the reaction vessel is connected to a reflux condenser and direct exposure is avoided. Conclusion: In conclusion, we have developed a simple, efficient, agro-waste-based catalytic approach for the synthesis pyrano[2,3-d]pyrimidine derivatives employing WELFSA as an efficient agro-waste-based catalyst under microwave conditions. The method is found to added advantages of less hazardous, eco-friendly, metal-free, chemical-free, short reaction time, simple workup and isolated product in good to excellent yields.

Sulphate-substituted tricalcium phosphate β-TCP: Effect of SO42− insertion and microwave conditions

In the present work, we have successfully synthesized pure β-TCP and sulphate substituted β-TCP by a wet chemical method derived microwave irradiation technique. XRD and FTIR results showed that the insertion of the SO42− group at PO43− sites, without microwave treatment, decreases the crystallinity of β-TCP samples and promotes the growth of calcium pyrophosphate β-CPP as a secondary phase. Our results also showed that wet chemical preparation combined with microwave treatment for TCPS-M led to a decrease in peak intensity, crystallite size average, as well as the peak broadening, confirming the decrease in degree of crystallinity. The average crystallite size of samples decreases from 46 to 21 nm. Besides, we noted a slight shift of XRD peaks towards a lower diffraction angle, which could be explained by the replacement of PO43− ions, with a smaller anionic radius of 0.238 nm, by SO42− ions with larger anionic radius of 0.258 nm. The FTIR analysis revealed the presence carbonate groups and the formation of β-CPP as a secondary phase for sulphate substituted β-TCP, confirming the XRD results. The Ca/P molar ratios were calculated using the ICP/AES technique. Furthermore, the SEM micrograph of SO42− substituted β-TCP demonstrates the deposition of β-CPP on β-TCP surface, supporting the XRD and FTIR results. These results emphasize that microwave irradiation and insertion of SO42− in the β-TCP matrix affect the degree of crystallinity and increase structural disorder.

Mechanistic Study of a Microwave Field-Controlled Static Crushing Agent for Efficient Rock Breaking.

The long reaction time and uncontrollable reaction process of the swelling agent in the process of rock breaking by static crushing agent lead to unsatisfactory efficiency and effect of rock breaking. This paper uses physical experiments to compare and analyze the changes in temperature and pressure of the hydration reaction under different microwave conditions; utilizes microscopic analysis of the hydration reaction products under each condition, combined with numerical calculations to elucidate the mechanism of the effect of microwave field on the hydration reaction of the expansion agent; and proposes a microwave field-controlled static crushing agent rock-breaking method. The study reached the following main conclusions: (1) microwave heating is better than conventional heating in terms of heating rate, peak temperature, and peak pressure; (2) using static crushing agent rock breaking is preferable to use a low-power microwave field to control the reaction process, and to ensure that the initial temperature is not higher than the local water boiling point; (3) microwave heating to promote the reaction mechanism lies in its deep heating of the system, faster heating rate, and higher energy utilization, and is more conducive to hydration expansion reaction; (4) selective heating of microwaves can enhance the hydration reaction of calcium oxide and inhibit the production of hydrated tricalcium silicate, making the reaction more complete, while microwave heating will also improve the microstructure of hydration products.

Dielectric properties of organic sulfur components and application in coal microwave desulfurization

ABSTRACT Changes in the dielectric properties of benzene mercaptan, benzene sulfide, and dibenzothiophene at 915 MHz frequency within 20 °C–100°C was studied for the first time. Coal-like substances were prepared by loading the compounds onto low-sulfur coal, and desulfurization test was performed under the microwave condition of 915 MHz and microwave – HCOOH–H2O2 system. The desulfurization reaction path and mechanism were summarized, and the relationship between the dielectric properties of organic sulfur and desulfurization efficiency was established. Results showed that the microwave-absorption ability of dibenzothiophene was weaker than that of benzene mercaptan and phenyl sulfide, and its dielectric properties changed irregularly with temperature. Dibenzothiophene cannot be removed by microwave radiation. Benzene mercaptan and phenyl sulfide had the highest efficiency of absorbing microwave energy and converting it into heat energy at 60°C. Moreover, they have the highest microwave desulfurization rate of up to 14%. In the microwave – HCOOH–H2O2 oxidation system, the highest desulfurization rates of phenyl sulfide occurred at 100°C because water-soluble products (such as sulfonate and sulfate) increased in the oxidation products. However, phenyl sulfide still had the highest desulfurization efficiency at 60°C. The desulfurization rates at 60°C and 100°C were 38% and 51%, respectively.

Efficient and Recyclable Solid-Supported Pd(II) Catalyst for Microwave-Assisted Suzuki Cross-Coupling in Aqueous Medium.

Solid-supported catalysts play efficient and crucial roles in organic synthesis. A solid-supported palladium(II) complex based on chitosan was synthesized and fully characterized using all possible tools (Fourier transform infrared spectroscopy, thermogravimetry analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectrometry, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller analysis). The catalytic activity of the solid-phase catalyst in Suzuki cross-coupling reactions was evaluated in aqueous solvents under both conventional heating and microwave irradiation conditions. The recyclability and thermal stability of the prepared catalyst were also examined, and the catalyst was found to be active till five consecutive runs without a notable loss of activity under the microwave condition, with the turnover number and turnover frequency values reaching 19,019 and 114,114 h–1, respectively.

Pincer-Cobalt-Catalyzed Guerbet-Type β-Alkylation of Alcohols in Air under Microwave Conditions

Pincer complexes of the type (R2NNN)CoCl2 (R = iPr, tBu, Cy, Ph, p-F-C6H4) derived from the environmentally benign, earth-abundant, and inexpensive base metal cobalt have been synthesized that exist in equilibrium with [(R2NNN)2Co]CoCl4. Among these complexes, (iPr2NNN)CoCl2 has been found to be highly efficient for the catalytic β-alkylation of alcohols in air at 140 °C. While the pincer-Co (0.0025 mol %)-catalyzed β-alkylation in the presence of NaOtBu (2.5 mol %) took 24 h (85%, 34000 TON at 1417 TO/h) under conventional heating (140 °C), the corresponding reaction under microwave conditions (140 °C at 75 W) was complete in only 2 h with comparable yields (83%, 33200 TON), albeit with a better TOF (16600 TO/h). In contrast, CoCl2 (0.0025 mol %) under otherwise identical conditions leads to lower yields under both conventional (66%, 26400 TON at 1100 TO/h) and microwave heating (61%, 24400 TON at 12200 TO/h). The catalytic system has been successfully implemented (39 examples) to accomplish the β-alkylation of secondary alcohols with several primary alcohols. Well-defined molecular Co(II) species are involved during catalysis, as inferred from HRMS and hot-filtration experiments. EPR studies and magnetic moment measurements using the Evans method demonstrate that Co remains in its +2 state and in an octahedral geometry throughout the reaction. Pivotal evidence for the involvement of β-hydride elimination leading to acetophenone in the RDS of the pincer-Co catalyzed β-alkylation is obtained from competitive deuterium labeling experiments, which are indicative of a KIE of 6.14. The current report on base-metal catalysis in air under microwave conditions that leads to high yields of β-alkylation with unprecedented turnovers (33200 TON at 16600 TO/h) in a very short time (2 h) offers exciting atom-economical and greener possibilities for these class of synthetically valuable Guerbet-type reactions.

Green Design, Synthesis, and Molecular Docking Study of Novel Quinoxaline Derivatives with Insecticidal Potential against Aphis craccivora.

An efficient and environmentally friendly method was established for designing novel 3-amino-1,4-dihydroquinoxaline-2-carbonitrile (1) via the reaction of bromomalononitrile and benzene-1,2-diamine under microwave irradiation in an excellent yield (93%). This targeted amino derivative was utilized for the construction of a series of Schiff bases (8–13). A new series of thiazolidinone derivatives (15–20) were synthesized in high yields (89–96%) via treatment of thioglycolic acid with Schiff bases (8–13) under microwave irradiation in high yields (89–96%). Moreover, new pyrimidine derivatives (26–30 and 35–38) were prepared by treatment of compound 1 with arylidenes (21–25) and/or alkylidenemalononitriles (31–34) using piperidine as a basic catalyst under microwave conditions. Based on elemental analyses and spectral data, the structures of the new assembled compounds were determined. The newly synthesized quinoxaline derivatives were screened and studied as an insecticidal agent against Aphis craccivora. The obtained results indicate that compound 16 is the most toxicological agent against nymphs of cowpea aphids (Aphis craccivora) compared to the other synthesized pyrimidine and thiazolidinone derivatives. The molecular docking study of the new quinoxaline derivatives registered that compound 16 had the highest binding score (−10.54 kcal/mol) and the thiazolidinone moiety formed hydrogen bonds with Trp143.

Puffing characteristics of berry slice under continuous microwave puffing conditions

To elucidate the puffing characteristics of the berry slice under continuous microwave conditions, heat and mass transfer and deformation of slices were investigated based on the models of coupled multi-physics fields involving electromagnetic heating, heat and mass transfer and solid mechanics. The results indicated that transmission mode of microwaves in a microwave cavity determined the electric field distribution inside slices with interior focusing phenomenon described by higher temperature and lower moisture content at the central region of slices than that of edge. The berry slice volume showed a “invisible-rapid-maintained” deformation under the synergistic effects of temperature, moisture and internal pressure with sample movement. This study may provide guidance for the elucidation of microwave puffing process of the moving slice and the underlying applications such as technology optimization and quality control of slices like berry. Novelty impact statement This work investigates the puffing characteristics of the moving berry slices under a continuous microwave dryer, and elucidates the heat and mass transfer and deformation process of berry slices by means of experiment and simulation. The distribution of alternating electric field profiles with high and low levels determine the absorption of microwave energy, heat and mass transfer in berry slices to induce the volume deformation and uneven distribution. The volume of berry slices laid on moving conveyor belt under continuous microwave puffing undergoes three deformation trends as invisible change followed by rapid expansion till desired shape.

Synthesis of Bioactive Yttrium-Metal-Organic Framework as Efficient Nanocatalyst in Synthesis of Novel Pyrazolopyranopyrimidine Derivatives and Evaluation of Anticancer Activity.

Novel Yttrium-metal–organic framework (Y-MOF) was synthesized under optimal conditions of microwave with a power of 20 W, the temperature of 30 degrees of centigrade, and time duration of 10 min. The products were characterized by SEM (morphology and size distribution), TGA (thermal stability), BET technique (surface area), and FTIR (characterization of the related group). The Yttrium-metal–organic framework (Y-MOF) synthesized in this study, after identifying and confirming the structure, was used as an efficient and recyclable catalyst in the synthesis of new pyrazolopyranopyrimidine derivatives. Following the study of the properties and applications of Y-MOF, its anticancer properties on breast cancer cells based on the MTT method were evaluated, and significant results were observed. In addition, the anticancer properties of the pyrazolopyranopyrimidine derivatives were investigated.

An Efficient CuI-Catalyzed C–S Cross-Coupling Reaction under Microwave Irradiation in DMF

AbstractMicrowave irradiated C–S cross-coupling reaction to synthesize 5-aryllthiobenzo-2,1,3-thiadiazole derivatives from a variety of benzene thiols with 5-bromo-2,1,3-benzothiadiazole, catalyzed by Cu(I) iodide and potassium carbonate as a cost-effective base in DMF, was conducted, affording excellent yields of the desired products. Microwave conditions assisted in the development of C–S cross-coupling reaction with higher yields.

Novel Spiro-pyrrolizidine-Oxindole and Spiropyrrolidine-Oxindoles: Green synthesis under Classical, Ultrasonic, and microwave conditions and Molecular docking simulation for antitumor and type 2 diabetes

Novel spiropyrrolizine / pyrrolidineoxindole moieties were synthesized chemo-, and regio-selectively in high yields from knoevenagel reaction of bis[arylmethylidene]piperidin-4-ones, isatin and L-proline or sarcosine under classical, ultrasonic, and microwave conditions. Seven derivatives of the synthesized dispiro-pyrrolizidine-oxindole and spiropyrrolidine were screened for their antitumor activity against two cell lines MCF-7 (breast cancer) and HEPG2 (liver cancer). The results of biological activity indicated that the tested derivatives showed potent activity against breast cancer cell MCF-7. Molecular docking simulation screening studies of the synthesized products with each of the receptors of (3hb5) for breast cancer and (4k9g) for liver cancer and their interaction with 1H5U of glycogen phosphorylase B, type 2 diabetes drug were examined. The docking study of dispiro-pyrrolizidine-oxindole and spiropyrrolidine showed promising results with several derivatives.

Loading of g-C3 N4 on Core-Shell Magnetic Mesoporous Silica Nanospheres as a Solid Base Catalyst for the Green Synthesis of some Chromene Derivatives under Different Conditions.

Using heterogeneous basic catalysts has a great importance in chemical reactions because of their advantages (such as easy separation and thermal stability at harsh conditions) over homogeneous catalysts. In this study, magnetic mesoporous silica nanoparticles (mSiO2) containing graphitic carbon nitride layers (mSiO2/g‐C3N4(x)) were fabricated through a facile process (x signifies the amount of melamine applied during synthesis). Graphitic carbon nitride layers were decorated on mSiO2 by calcination of immobilized melamine (as graphitic carbon nitride precursor) on mSiO2 in the last step of catalyst synthesis. The structure of the prepared catalysts was confirmed using XRD, BET, FESEM, EDX, elemental mapping and TEM methods. The catalytic efficiency of the so‐obtained solid base composite was investigated for the synthesis of some dihydropyranochromenes and spiro‐dihydropyranochromenes under thermal and microwave conditions. Using mSiO2/g‐C3N4(x) led to high yields under green conditions and in short reaction times and without a decrease in catalytic activity after four consecutive cycles.

Fast and Efficient Synthesis of Racemic Baloxavir Catalyzed by Strong Solid Acid under Microwave Conditions

The compound (±)-12aR-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiepin-11-yl]-7-hydroxy-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione is the intermediate of baloxavir marboxil. In the literature, traditional heating methods and common acid catalysts are used, which result in long reaction times and a low yield. Therefore, finding an efficient and environmentally friendly synthetic route is necessary. In this study, (±)-12aR-12-[(11S)-7,8-difluoro-6,11-dihydrodibenzo[b,e]thiepin-11-yl]-7-benzyloxy-3,4,12,12a-tetrahydro-1h-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione (compound 3) was synthesized using a sulfonate resin solid acid catalyst (HND-580) under microwave conditions. The benzyl group was removed without further purification, and an intermediate, racemic baloxavir, was obtained under microwave irradiation. The total yield of the two steps was 78%. This method greatly reduces the reaction time and improves production efficiency.

Microwave‐Assisted Copper‐Catalyzed One‐Pot Synthesis of 2‐Aryl/Heteroaryl‐4‐Quinolones via Sequential Intramolecular Aza‐Michael Addition and Oxidation

AbstractA protocol has been developed that allows the synthesis of 2‐aryl/heteroaryl‐4‐quinolones from readily available, affordable starting materials. The reaction proceeds under microwave conditions with moderate to high yields in the presence of copper catalyst. Short reaction time, good functional group tolerance, high atom economy, non‐toxic byproduct and no use of special ligands emphasize the applicability of this method in organic synthesis.

Effect of chemical desulfurization on coal properties and sulfur structure based on microwave technology

AbstractUnder the two frequency microwave conditions of 915 and 2450 MHz, orthogonal tests were designed to investigate the effects of organic acid reagent, microwave irradiation time, and mixing time of additives and coal samples on the desulfurization effect of coal. Results show that the effect of irradiation time on the experimental desulfurization efficiency under frequency microwave conditions is large and is the main factor. The desulfurization effect under 915 MHz microwave condition is better than 2450 MHz microwave condition. Two sets of experimental optimal coal samples were used for characterization and analysis. Thermogravimetric analysis revealed that the combustion temperature range of the coal samples is shortened and the integrated combustion index is considerably higher after the microwave irradiation experiment. Fourier‐transform infrared spectroscopy analysis showed that the overall chemical structure of the coal samples does not change significantly after the experimental treatment. X‐ray photoelectron spectroscopy analysis showed that the intensity of organic sulfur in coal samples is weakened after microwave irradiation, the characteristic peaks of thiols and thioethers are reduced to a great extent, and an increase in the intensity of sulfoxide organic sulfur is observed. On the basis of the results of experimental analysis and quantum chemical simulation calculations, the mechanism of organosulfur structure removal under the action of microwave is revealed.

Enhancement of bio-oil quality over self-derived bio-char catalyst via microwave catalytic pyrolysis of peanut shell

Studies have indicated that a low-cost and high-efficiency treatment process is essential for converting agricultural waste into liquid fuels or chemicals. In the present work, the self-derived bio-char from peanut shell pyrolysis with the loading of selective transition metals (Fe, Co and Zn) were used as a catalyst for the production of more aromatic hydrocarbon contained bio-oil from the microwave pyrolysis of peanut shells. Py-GC/MS analysis results revealed that 10% loaded Fe/Bio-char increased the hydrocarbons in the bio-oil from 3.96% to 38.09%, and selectively, the aromatics hydrocarbon increased from 2.33% to 24.57%. The central combination design (CCD) optimized the microwave pyrolysis temperature and the catalyst to raw material ratio. The response surface area analysis showed that the temperature greatly influences aromatic hydrocarbon production more than the catalyst ratio to the substrate. At the pyrolysis temperature of 550 ℃ and the catalyst/peanut shell of 20%, the bio-oil yield was 24.3%, where the selectivity of hydrocarbon and aromatic hydrocarbon reached the maximum of 26.97% and 17.95%, respectively. The study of self-derived bio-char and the usage as a catalyst in pyrolysis of raw peanut materials under microwave conditions would be a high-value application for catalytic pyrolysis reactions to improve the utilization rate of biomass, reduce the reaction costs, and provide theoretical basis and technical support for the recycling and total utilization of agricultural waste.

Investigating the microwave parameters correlating effects on total recovery of bioactive alkaloids from sesame leaves using orthogonal matrix and artificial neural network integration

In this study, the microwave-assisted processing of Sesamum indicum leaves was intensified to predict the total alkaloid content via Taguchi orthogonal design and neural network model. Under the optimum microwave condition, the maximized alkaloid content was estimated to be 15.40 (mg/g) % using irradiation time (A) of 60 sec, microwave power (B) of 300 W, oven temperature (C) of 60°C, the mass ratio (D) of 12.5 g/ml, and solvent concentration (E) of 80%. The significant effects of each microwave extraction parameter declined in the order listed: C > B > A > D > E which indicated a 31 and 29% contribution of microwave power and oven temperature, respectively. Moreover, higher coefficients of determination (R2 = 0.9999), and a decreased mean square error (MSE) of 2.69E-07 suggest good accuracy in predicting total bioactive alkaloid recovery, as proven by cross-validation trials. Under these microwave conditions, a total of 115 alkaloids were tentatively identified with lindelofine (m/z = 308.18) and supinin (m/z = 306.17) being the most abundant pyrrolizidine alkaloids. Novelty impact statement Although many researchers reported the total alkaloids recoveries from different parts of Sesame plant; the process intensification of microwave processing from leafy parts using Taguchi design and ANN approach have not been investigated. This study established an optimum condition for the total recovery of alkaloid content from S. indicum using orthogonal optimization methodology and artificial neural network

Dielectric properties and microwave heating behaviour of a recycled copper blast furnace ash

ABSTRACT Aiming at the problem that persistent organic pollutants (POPs) are difficult to degrade under traditional process conditions, this paper studies the dielectric properties and temperature rise characteristics of regenerated copper ash in microwave field to provide theoretical support for the removal of POPs under microwave conditions. The experimental results show that the dielectric constant (), dielectric loss factor () and the loss tangent () increase with the bulk density. The value of increases with temperature, the values of and first increase and then decrease with the temperature. When ρ = 0.76 g/cm3, increased from 6.5 to 10.136, the maximum values of and were 0.0627 and 0.0983. When ρ = 1.06 g/cm3, increased from 7.5 to 34.472, the maximum values of and were 0.344 and 0.0385. When ρ = 1.36 g/cm3, increased from 9 to 34.146, the maximum values of and were 0.386 and 0.040. In addition, the higher the microwave power, the faster the copper ash temperature rises, and the water content promotes the heating speed.

Silicomolybdic acid intercalated graphene oxide-based solid acid: catalytic activity and investigation of structural stability by DFT analysis

Silicomolybdic acid supported graphene oxide (GO-SMA) was synthesized via a simple impregnation method and demonstrated as an active catalyst for the efficient synthesis of biologically important molecule (isoxazoles) under green and efficient microwave condition. The structural and morphological variation of the catalyst was investigated by a number of sophisticated characterization techniques. For the detection of acidic sites on GO-SMA surface, NH3-TPD and pyridine IR spectroscopic studies were carried out and revealed the presence of a significant amount of acidic sites (0.62 mmol g−1) which are essential for heterogeneous acid catalysis. A Density Functional Theory (DFT) method had revealed that our catalyst is thermodynamically stable as the binding energy was found to be (−56.28 kcal/mol). Also, it was found that reactant molecules were efficiently adsorbed on the catalyst surface which enhanced the catalytic activity. Besides high catalytic activity and a wide variety of substrate scope this catalyst showed good recyclability up to five successive cycles with minimum loss of activity.

Synthesis of Schiff Base Complexes of Lanthanides in Microwave Assisted via Eco Friendly Method

Some new Schiff base complexes of dysprosium derived from alpha napthyl amine with different benzaldehyde. Reactions were carried out under microwave conditions. The ligands and their dysprosium complexes show a good activity against the bacteria S.aureus E.coli and fungi Penicillium Crysogenum, Aspergillus niger. The Schiff bases and their dysprosium complexes show variable activity of inhibition on the growth of bacteria.