Current Microwave Chemistry - Volume 6, Issue 1, 2019

Introduction: New methods for preparing surface modification of flame retardant cotton fabrics were employed by applying a microwave-assisted technique with a minimum amount of co-solvent. Efforts at flame retardant cotton fabrics treated with economic and environmentally friendly flame retardant compounds based on the small molecules piperazine, PN and PNN, were done successfully. Methods and Results: The evidence of flame retardant chemical penetrations or surface modification of cotton fabrics was confirmed by Scanning Electron Microscope (SEM), and the treated cotton fabrics were evaluated by flammability tests, such as 45°angle (clothing textiles test) and limiting Oxygen Index (LOI). Thermogravimetric analysis of all treated cotton fabrics in a nitrogen atmosphere showed high thermal stability, as decomposition occurred between 276.9~291.2°C with 30.5~35.7% residue weight char yield at 600°C. Limiting Oxygen Index (LOI) and the 45° angle flammability test were used to determine the efficiency of the flame-retardant treatments on the fabrics. LOI values for control twill fabric showed ~18 vol% oxygen in nitrogen, whereas the highest treatment level had 32 vol%. High add-on treatments with flame retardants also readily passed the 45° angle flammability test. Conclusion: In the Microscale Combustion Calorimeter (MCC) tests, a decline in heat of combustion was shown through the smaller values acquired for THR, HRC and Tmax for all PN and PNN samples.

Background: Nowadays, microwave assisted techniques are becoming popular ecofriendly approaches in Green Chemistry. However, to date, no study has reported the microwave assisted graft copolymerization of acrylamide on carboxymethyl xanthan gum backbone. Objective: The objective of this study was to study the effect of microwave radiations on graft copolymerization of acrylamide on carboxymethyl xanthan gum. Methods: Carboxymethyl xanthan gum was grafted with acrylamide under microwave irradiation. The grafting process is optimized by varying the amount of carboxymethyl xanthan gum, acrylamide, ammonium persulphate, microwave power and exposure time. The graft copolymer was further characterized and evaluated for its efficacy. Results: Grafting was successfully optimized for higher grafting efficiency (92.4 %) and grafting (410.5 %) in a short reaction time of 150 s, at 40 times less concentration of ammonium persulphate. The characterization study confirmed the grafting of acrylamide on the hydroxyl group of carboxymethyl xanthan gum backbone. Conclusion: Microwave radiations play a vital role in graft copolymerization of acrylamide on carboxymethyl xanthan gum, in short reaction time, at 40 times less concentration of initiator. The synthesized graft copolymers remain nontoxic and also showed more antimicrobial activity than carboxymethyl xanthan gum.

Background: Benzimidazole is the fused heterocyclic aromatic compound. It is an essential pharmacophore and privileged structure for the development of new drug molecules. These are bioactive molecules present in various anthelmintic drugs such as albendazole, mebendazole, parbendazole, triclabendazole etc. Methods: Benzimidazole derivatives are synthesized by reaction between orthophenylene diamine and anthranillic acid followed by acetylation in the presence of acetic anhydride. Finally, the acetylated products undergo Claisen-Schimdt condensation with various substituted benzaldehydes to produce corresponding benzimidazole derivatives or chalcones. Both conventional and microwave irradiation technology are followed to get the titled compounds. The titled compounds are screened for their anticonvulsant and neurotoxicity activity. Results: By the help of microwave synthesis, the yield of product was increased in less reaction time. So, it follows Green chemistry approach by making above reactions eco-friendly. Some of the compounds exhibited significant anticonvulsant activity as compared to standard drug. Conclusion: In the present investigation, we have synthesized novel benzimdazole derivatives with chalone moiety to improve the biological activity. The compounds were obtained under microwave reaction with high yield in a short reaction time.

Background: The agricultural wastes as a source offer an excellent alternative to replace many toxic and environmentally hazardous catalysts, due to their least toxicity, ease of biodegradability, and ability to act as a greener catalytic medium. Some of the agro-waste based catalysts reported are BFE, WERSA, WEB, and WEPBA. 2-Amino-4H-chromene derivatives are promising biologically potent heterocyclic compounds, due to their medicinal applications such as antimicrobial, anti-inflammatory, antibacterial, antiviral, anticancer, antidiuretic, anticoagulant and antianaphylactic activities. The present work describes a microwave accelerated, efficient, eco-friendly and economical approach for the synthesis of 2-amino-4H-chromenes through condensation of substituted arylaldehyde, malononitrile and resorcinol/naphthol catalyzed water extract of pomegranate peel ash (WEPPA) under microwave irradiation. The reaction completed within 3-6 min with good to excellent yield of product isolation. The final product isolated by simple filtration and recrystallization gave a spectroscopically pure form of product and did not require further purification. Methods: The pomegranate peel ash water extract as an agro-waste derived catalyst was employed under microwave irradiation for the economical synthesis of 2-amino-4H-chromene derivatives. Results: The reported agro-waste based catalyst was obtained in the absence of external base, additives and solvent-free synthesis of 2-amino-4H-chromene using aryl aldehyde, malononitrile and resorcinol/ naphthol under microwave irradiation. WEPPA acts as a solvent media and catalyst, as it plays a dual role in the synthesis of 2-amino-4H-chromenes. Conclusion: We established an efficient, simple, agro-waste based catalytic approach for the synthesis of 2-amino-4H-chromene derivatives from the condensation of arylaldehyde, malononitrile and resorcinol/α-naphthol/β-naphthol employing WEPPA as an efficient catalyst under microwave synthesis. The method has found to be a greener, economic and eco-friendly approach for the synthesis of chromene scaffolds. The advantages of the present approach are solvent-free, no external metal, chemical base free, short reaction time and isolated product in good to excellent yields. The catalyst is agro-waste derived, which has abundant natural sources available, thus making the present approach a greener one.

Background: This paper describes the synthesis of novel thiazolidin-4-one substituted pyrazole derivatives from the condensation reaction of hydrazide with acetophenone derivatives. Herein we describe the synthesis of fourteen compounds by microwave irradiation method. The synthesized compounds are in excellent yield by utilizing microwave irradiation heating. Objective: Compounds using different aromatic or heteroaromatic compounds should be synthesized and screened for their antibacterial activity to explore the possibility of pyrazole substituted thiazolidin- 4-ones as a novel series of antimicrobials. Methods: Synthesis of thiazolidin-4-one substituted pyrazole derivatives was carried out under microwave radiation. Results: These compounds were identified on the basis of melting point range, Rf values, IR, 1HNMR and mass spectral analysis. These compounds were evaluated for their in vitro antimicrobial activity and their Minimum Inhibitory Concentration (MIC) was determined. Among them Comp. 4b and Comp. 4k possess appreciable antimicrobial and antifungal activities. Conclusion: A novel series of Thiazolidin-4-one substituted pyrazole were synthesized under microwave irradiation method and identified on the basis of melting point range, Rf values, IR, 1HNMR, mass spectral data and elemental analysis. The compounds were subjected to in vitro antimicrobial screening and their Minimum Inhibitory Concentrations (MIC) were determined. Among all the tested compounds, two compounds 4b and 4k exhibited moderate to significant activity against all the tested strains of bacteria and fungus were found to have appreciable antimicrobial activities. The results of antibacterial activity showed that compounds containing electron withdrawing groups were found to be more active than the compounds containing electron releasing groups.

Background: The Knoevenagel condensation is an important reaction in organic chemistry because of its capacity to form new C-C bonds and its products are mainly used in organic synthesis as intermediates, due to the large number of reactions they can undergo. Based on the importance of the Knoevenagel adducts, a sustainable synthetic methodology was developed employing microwave irradiation. Objective: Develop a synthetic methodology employing microwave irradiation and green solvents to obtain Knoevenagel adducts with high yields. Methods: Knoevenagel condensation reactions were evaluated with different basic catalysts, as well as in the presence or absence of microwave irradiation. The scope of the reaction was expanded using different aldehydes, cyanoacetamide or methyl cyanoacetate. The geometry of the formed products was also evaluated. Results: After the optimization process, the reactions between aldehydes and cyanoacetamide were performed with triethylamine as catalyst, in the presence of microwave irradiation, in 35 minutes, using NaCl solution as solvent and resulted in high yields 90-99%. The reactions performed between aldehydes and methyl cyanoacetate were also performed under these conditions, but showed better yields with EtOH as solvent 70-90%. Finally, from X-ray analysis, the (E)-geometry of these compounds was confirmed. Conclusion: In this study we developed synthetic methodology of Knoevenagel condensation using triethylamine, green solvents and microwave irradiation. In 35 minutes, products with high yields (70- 99%) were obtained and the (E)-geometry of the adducts was confirmed.

Background: For rapid and sustainable synthesis, microwave irradiation method is serviceable. This present study deals with the preparation of oxadiazole and pyridine bearing 1,2,3,4- tetrahydro pyrimidine derivatives by microwave irradiation. Objective: The present study aims to carry out rapid synthesis of chloro-acetamides of oxadiazoles of Biginelli product and amino cyano derivative of pyridine by microwave-assisted heating. Our efforts are focused on the introduction of chemical diversity in the molecular framework in order to synthesize pharmacologically interesting compounds. Methods: Microwave irradiation was used for the synthesis of 2-((3-cyano-4-(3,4-dichloro phenyl)- 6-(4-hydroxy-3-methoxyphenyl) pyridin-2-yl) amino)-N-(5-(substituted) -(6-methyl-2-oxo -1,2,3,4- tetrahydro pyrimidin-5-yl)-1,3,4-oxadiazol-2-yl)acetamide by using Biginelli reaction. New structural analogues were confirmed by spectral studies followed by their screening for in vitro antibacterial activity against Staphylococcus aureus, Staphylococcus Pyogenus, Escherichia coli and Pseudomonas aeruginosa bacterial strains and for antifungal activity against Candida albicans, Aspergillus niger and Aspergillus clavatus by micro-broth dilution method. In vitro antimycobacterial activity determined out against (Mycobacterium tuberculosis) H37Rv strain using Lowenstein-Jensen medium. Results: As compared to the conventional method, microwave irradiation method is advantageous for the synthesis of 1,2,3,4-tetrahydropyrimidin derivatives. Potent antimicrobial activities and antitubercular activity were found for some of the compounds. Conclusion: Microwave irradiation method provided an effective way to discover a novel class of antimicrobial and antituberculosis agents. 1,2,3,4-tetrahydropyrimidin derivatives showed improved antimicrobial and good antituberculosis activity.