Current Microwave Chemistry - Volume 5, Issue 2, 2018

Background: Expand of industrial activity elevates the question of waste water treatment containing heavy metal ions. Removal of lead ions from industrial wastewater has immense scientific and practical interest. Adsorption is a promising technique due to its easy handling, high efficiency, and availability of different adsorbents. Graft copolymerization of natural polysaccharides is becoming a very important resource to develop superior materials for adsorption of heavy metals. Methods: In this study, graft copolymer of gellan gum and polyacrylamide was synthesized by a microwave-assisted method using a very low concentration of potassium persulphate for the biosorption of Pb++ ions from aqueous solution. Fourier transform infrared spectroscopy, scanning electron microscopy, x-ray diffraction, and differential scanning colorimetry were used to characterize the graft copolymer. Results: The optimum grafting was observed when the reaction mixture containing 20 x10-3 mol/L potassium persulphate; 71.42g/L polyacrylamide and 10.71g/L gellan gum, when exposed to 800W microwave power for 120s. The sorption process is pH dependent and maximum sorption was obtained at pH 5. The sorption data were found to obey both Langmuir and Freundlich sorption isotherms but Langmuir isotherm proved to be a better mathematical fit for equilibrium data than Freundlich model. A metal capped structure was observed by SEM analysis after Pb++ ions biosorption. Conclusion: Present study concluded that microwave assisted synthesized gellan gum based bioadsorbent has potential to be used in wastewater treatment.

Background: Organic synthesis using microwave is one of the good alternative method for becoming progressively more extensive in the modern organic synthesis. It shows numerous advantages like reduce the reaction time, decrease energy consumption, reduces side reactions, improve reproducibility and increases the product yields. Multicomponent Reactions (MCRs) are one of the method for convenient and facile conversion of simple readily available substrates into novel and extremely diverse compound libraries by the use of one-pot synthesis. MCRs are influenced by microwave and as a potent green alternative over the conventional synthesis. Many researcher have done tremendous research work on Spiroheterocyclic compounds. Coumarin is one of the major classes of naturally occurring compounds and having continues interest in chemistry because of its usefulness as biologically active agents. Synthesis of new and desired compounds have an endless demand. As a part of our ongoing research in the area of synthesis of spirooxindole derivative, We described a rapid, efficient, one-pot three component microwave assisted method for the synthesis of chromenylspiro[indoline-3,2'-pyrrolidin]-2-one derivatives from the reaction between isatin, sarcosine and 4-(allyloxy)-2H-chromen-2-one derivatives by using p-TSA as an prompt catalyst. All the synthesized compounds are subjected to in-vitro antibacterial activity using four different bacterial stain. Methods: A mixture of 4-(allyloxy)-2H-chromen-2-one derivatives (3a-3c) (0.01 mmol), isatin (0.01 mmol) and sarcosine (0.01 mmol) in 5 ml methanol were irradiated in microwave (CEM microwave) at 300 W for 10-25 minutes in the presence of p-TSA (10 mol%). The completion of the reaction was indicated by TLC (30% ethyl acetate-hexane). The reaction mixture was allowed to cool at room temperature and was then poured into ice water. The resulting solid residues were filtered off, dried to get the crude product which was further recrystallized from methanol or ethanol to get targeted product 1'-methyl-4'-(((2-oxo-2H-chromen-4-yl)oxy)methyl) spiro[indoline-3,2'-pyrrolidin]-2-one derivatives (6a-6i) in very good yield. Results: In the recent study, it has been understood that the catalysts have a major role in the organic synthesis. We optimized the reaction conditions, The one-pot, three-component cyclization reaction of 4-(allyloxy)-2H-chromen-2- one derivatives, various isatins, and sarcosine in the presence of p-TSA (10 mol%) as catalyst in methanol and complete reaction in only 12 minutes by using microwave irradiation to afford 1'-methyl-4'-(((2-oxo-2H-chromen-4- yl)oxy)methyl) spiro[indoline-3,2'-pyrrolidin]-2-one 6a in good yields. To achieve suitable conditions for the synthesis of targeted compound, various reaction conditions and catalysts have been investigated for reaction. Results showed that the reaction proceeds in the presence of all catalysts of the series and also reaction yields were better with p-TSA. The results were good in terms of yields and product purity in the presence of p-TSA as an inexpensive and easily available catalyst and so, it can be proved better than the others. The structure of the products were elucidated with the help of IR, 1H-NMR, mass spectral data, and elemental analysis. All the synthesized compounds were screened for their antibacterial activity out on Nutrient-agar plates by welldiffusion assay against test culture. Compounds 6g and 6i exhibited better zone of inhibition against Enterobacter aerogens gram negative bacteria. When compound 6c shows parallel activity to standard drug against Escherichia coli. For Micrococcus luteus, compounds 6f found to be very active than all other compounds in the series. Moreover, the compounds 6b and 6g displayed good activity against Bacillus cereus gram positive bacteria. Conclusion: In summary, we have reported an efficient, novel, one pot, three component protocol for the synthesis of chromenyl spiro[indoline-3,2'-pyrrolidin]-2-one derivatives by the reaction of isatin, sarcosine with diversified 4- (allyloxy)-2H-chromen-2-one derivatives using p-TSA as a quick catalyst under microwave assisted reaction. The main benefits of this present practice are the simplicity of the method, good yields, simple work up, and the ease of product isolation. Additionally, the existence of three different important heterocyclic moieties such as chromen, indoline, and spiro rings in one molecule is fantastic as a result of the prospective applications of these derivatives in biological as well as pharmacological activities. Furthermore, The Pharmacokinetic characterization and optimization of this series are under process in our laboratory.

Background: Pyranocarbazoles exhibit promising biological activities such as mosquitocidal, antimicrobial, anti-inflammatory and antioxidant. Pyranocarbazole derivatives have also been used in the field of medicinal chemistry as a pharmacophore for different therapeutic indications. Methods: New pyrano[3,2-c]carbazole derivatives have been synthesized by the reaction of carbazole Mannich bases with (E)-N-methyl-1-(methylthio)-2-nitroethenamine under microwave irradiation. This transformation presumably occurs via o-quinone methide-Michael addition-tautomerismintramolecular O-cyclization-elimination sequence of reactions creating new one C-O bond and one C-C bond. The structures of obtained pyranocarbazoles were confirmed by NMR, IR and mass spectra. Results: Various substituted carbazole Mannich bases such as fluoro-, nitro-, methoxy-, and trimethoxy-derivatives reacted smoothly to give the corresponding pyrano[3,2-c]carbazole derivatives in good yields. The significant features of this reaction include catalyst-free, solvent free, no column chromatographic purification, short reaction time and good yields. Conclusion: We have developed a simple and efficient synthesis of novel pyrano[3,2-c]carazoles derivatives under microwave irradiation in good yields. It is noteworthy that this reaction results in the formation of two new bonds (one C-C and one C-O) in a single operation.

Background: This paper describes the synthesis of novel fused heterocycles, from the reaction 2-cyano-N-cyclohexyl-3-acrylamide derivatives 5a-f with nitrogen nucleophilic reagents, which carried out under microwave irradiation. Reactivity of 3 towards diazonium amines salts to afford hydrazones undergo cyclization to give amino pyrazole and the fused heterocyclic compounds incorporating cyclohexyl moiety. The synthesized compounds excellently utilized microwave irradiation in short time and high yield. Methods: Synthesis of Fused heterocycles derivatives from 2-cyano-N-cyclohexyl acetamide utilizing Microwave irradaition. Results: Regioselective facile synthesis of innovative heterocycles from the reaction of 2-cyano-Ncyclohexyl acetamide (3) with appropriate aldehydes to afford the corresponding acrylamide derivatives 5a-f under microwave irradiation. Acrylamides 5 reacts with hydrazine derivatives affording the corresponding pyrazole derivatives 7a and 7b, furthermore the treatment of acrylamides 5 with 2-amino benzimidazole, amino pyrazole, and aminotriazole derivatives to gives corresponding pyrimido[1,2-a]benzimdazole 10, pyrazolo[1,5-a]pyrimidine 12 and triazolo[1,5-a]pyrimidine 14; respectively in good yield. Reactivity of 3 towards diazonium amines salts afforded hydrazones derivatives, which undergo cyclization to give the corresponding derivatives 19a and the fused pyrazolo[5,1-c][1,2,4]triazine 22, triazolo[5,1-c][1,2,4]triazine 24 and imidazo[2,1-c][1,2,4]triazine 28 incorporating cyclohexyl moiety. Conculsion: In this investigation, we have synthesized innovative pyrimido[1,2-a]benzimdazole, and triazolo[1,5-a]pyrimidine, pyrazolo[1,5-a]pyrimidine, 2-amino benzimidazole, amino pyrazole, aminotriazole, fused pyrazolo[5,1-c][1,2,4]triazine, triazolo[5,1-c][1,2,4]triazine and imidazo[2,1- c][1,2,4]triazine derivatives incorporating cyclohexyl moiety utilizing microwave irradiation. The compounds were obtained under microwave reaction in excellent yield in a short reaction time.

Background: The influence of the microwave effect in organic reactions is still not a completely clear issue. Higher temperature region (hot spots) in organic reactions have been observed and attributed to the selective heating mechanism of microwave irradiation. The accumulated heat in the polar reactants results in the acceleration of certain reactions. However, whether lower temperature region (cool spots) exists is not clear. Methods: On the basis of the microwave selective heating mechanism, less polar reactant allyl 4- methylphenyl ether was selected as a molecular probe and conducted Claisen rearrangement in more polar solvent N-methylpyrolinone in different concentrations. The temperatures of reactions under different conditions were deduced from Arrhenius equation. The dielectric constants of starting material allyl 4-methylphenyl ether, product 2-allyl-4-methylphenol, and solvent N-methylpyrolinone were determined under 2.54 GHz microwave irradiation conditions by use of the capillary method. Results: Lower temperature regions were observed in the Claisen rearrangement of allyl 4- methylphenyl ether in N-methylpyrolinone only in low concentration. However, they were not in high concentrations. The results of determination indicate that product 2-allyl-4-methylphenol shows higher polarity than reactant allyl 4-methylphenyl ether. This is a possible reason why lower temperature regions were not observed in reactions performed in higher concentrations because much more polar product was generated. Stirring speed does not affect temperature difference possibly due to the reason that microwave frequency is huge as compared with the stirring speed. Conclusion: Lower temperature regions were observed in the Claisen rearrangement of allyl 4- methylphenyl ether in N-methylpyrolidinone, an intramolecular reaction with a less polar reactant in a more polar solvent, followed by the first order kinetic. The results reveal the reason why some organic reactions cannot be accelerated because their reactants are located in lower reaction temperature regions (cool spots).

Background: Coumarin belongs to a group known as benzopyrones which consist of a benzene ring joined to a pyrone nucleus which possesses varied biological activities. The current work described the Microwave-assisted synthesis of various pyridyl pyrazoline substituted coumarins. These newly formed coumarin derivatives are characterized by spectra analysis and screened for their in vitro antimicrobial screening against bacterial and fungal pathogens by Broth dilution method. Methods: In the synthetic method, the target compounds were synthesized by reacting different coumarin chalcones with hydrazine hydrate in acetic acid or propionic acid and phenylhydrazine derivatives in acetic acid respectively with the help of microwave irradiation method. Results: The structures of all the synthesized compounds were established by IR, 1H-NMR, 13C-APT and some representative mass spectral data. The target compounds were also screened for their in vitro antimicrobial screening against a representative panel of bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Salmonella typhi) and fungi (Aspergillus niger and Candida albicans). Conclusion: In conclusion, the final products were obtained by utilizing Microwave Irradiation (MWI) technique in excellent yields with a short reaction time. Among all the synthesized compounds, 3a, 3d, 7a and 7c were found to have significant activity against bacterial and fungal strains.

Background: Algae gain is of much importance in food and pharmaceutical industries due to the presence of rich bioactive compounds. Methods: A Microwave Assisted Extraction (MAE) was engaged to enhance recovery of bioactive compounds from Dunaliella bardawil. The effective experimental condition was identified by optimization using Response Surface Methodology (RSM) coupled with Central Composite Rotatable Design (CCRD) along with Adaptive Neuro-Fuzzy Inference System (ANFIS). In this connection, four independent parameters, namely, n-hexane concentration (X1:60-85%), microwave power (X2:15- 25%), radiation-induced temperature (X3:40-60°C) and radiation exposure time (X4:7.5-12.5min) were chosen. Results: The optimum conditions resulted in 72.34-75.86% of biomass (y1) and 46.27-47.17 mg of β- carotene equivalents/g to biomass (y2). In addition, the corresponding antioxidant activities showed 85.65-85.90% in DPPHsc (y3), 81.30-81.31% in ABTSsc (y4) and 59.65-62.45 μgmol (Fe (II))/g in FRAP (y5). Further, the bioactive compounds, β-carotene, and lutein were identified through HPLC and the biomass exhibited significant anticancer activity against oral epithelial cancer cells. Conclusion: The observed results clearly highlight that the study has great scope and value for the continuation of further exploitation and application.

Background: Seeds are treated with phosphine (PH3) fumigant to protect them from insects while under storage. However, health concerns mean it is essential to quantify phosphine residues after fumigation. Residues are normally measured either after solvent extraction or purge and trap procedures, but there remain problems of solvent interference in measurements. Microwave irradiation is an excellent method to release PH3 from grain, but there are no reports of this being used on oilseeds. Methods: Three methods were compared to measure phosphine residues in canola and cottonseed: solvent extraction only, grinding plus solvent extraction, and microwave irradiation. The headspace concentration of PH3 was analysed by Gas Chromatography (GC) equipped with a Pulsed Flame Photometric Detector (PFPD). Completeness of microwave extraction was estimated from the amount of fumigant retained by the microwaved samples. This amount was determined by further microwave irradiation. Results: Recoveries of PH3 from fortified canola and cottonseed samples were 94.8±5.7% to 96.3±5.5% for the grinding plus solvent method and 95.8±6.1% to 96.4±7.1% for the microwave method. Quantitative results from microwave irradiation and the grinding plus solvent methods were similar. Yield from solvent extraction was 50% lower than that from the other methods tested. Completeness of microwave extraction was less than 5% of the amount obtained from the initial procedure. Limits of quantification were < 0.001 ng/g. Conclusion: The microwave method is rapid (<5 min per sample), solvent-free and requires only a small amount of sample.