APPLICATIONS OF MICROWAVE ENERGY IN ORGANIC CHEMISTRY. A REVIEW

Separation and extraction of non-thermal effects of strong microwave electric field on dielectric properties of materials based on time modulation and cavity perturbation method

The influence of strong microwave electric field (SMEF) on the dielectric properties of materials is the result of the joint action of microwave thermal effect and microwave non-thermal effect. Generally, the thermal effect of SMEF is stronger than the non-thermal effect, which makes the non-thermal effect of SMEF difficult to detect. Moreover, it is difficult to distinguish the influence of these two factors from each other. Therefore, the formation mechanism and characteristics of the non-thermal effect of SMEF have not been elucidated so far. In this paper, a separation and extraction model of the non-thermal effect of SMEF on the dielectric property of material is proposed based on the time modulation method and cavity perturbation method. By adjusting the interaction time between SMEF and materials, reducing the influence of microwave thermal effect, and strengthening the proportion of microwave non-thermal effect, the separation and extraction of the non-thermal effect of SMEF is realized. Through the designed re-entrant coaxial cavity, the corresponding test system is constructed and the typical materials are tested. Experimental results show that the proposed research method is feasible. The research method proposed in this paper provides an effective way for the follow-up study on the formation mechanism and characteristics of the non-thermal effect of SMEF on the dielectric properties of materials.

Microwave-Assisted Synthesis of Quinazolines and Quinazolinones: An Overview

Microwave irradiation (MWI), as a unique, effective, sustainable, more economic, and greener source of energy compared to conventional heating, is applied in different organic transformations to result in the rapid formation of desired compounds due to thermal/kinetic effects. In this review, we try to underscore the applications of microwave irradiation (MWI) in the synthesis of quinazoline and quinazolinone derivatives that have been achieved and reported on in the last two decades.

Recent Advances in Microwave Promoted C-P Cross-coupling Reactions

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Organophosphorous compounds are of potential importance in diverse fields. They are often used as intermediates for making functionalized phosphine ligands as well as find vast applications in the areas of industrial, agricultural and biological chemistry. The microwave-assisted synthesis of C-P bonds has become increasingly popular because of its various advantages over conventional heating in the perspectives of green chemistry.

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This review article has primarily focused on the synthesis of various organophosphorous molecules via microwave promoted C-P cross-coupling reactions under metal-catalyzed or metal–free conditions over the last two decades. The synthesis of phosphine ligands on 4,4′-bisquinolone structural framework, disubstituted phosphinic acid esters, vinyl phosphines, aryl- and vinylphosphonates, sugar and nucleoside phosphonates, aminobisphosphonates, triphenyl phosphines, water-soluble tertiary phosphine oxides and many other potentially useful organophosphorous compounds have been illustrated critically. The Hirao reaction, Michaelis-Arbuzov reaction and Sandmeyer type of reactions are generally involved in creating C-P bonds. The role of various metal catalysts, solvents, bases, additives and temperature in different literatures are carefully discussed.

Microwave assisted slurry conversion crystallization for manufacturing of new co-crystals of sulfamethazine and sulfamerazine

Formation of co-crystals is faster using microwaves than simple conductive/convective heating to the same temperature.

A Rapid and Convenient Synthesis of Oximes in Dry Media under Microwave Irradiation

In a novel method, the reaction of hydroxylamine hydrochloride with a number of aldehydes and ketones under microwave irradiation and solventless ‘dry’ condition gave oximes in excellent yield.

Montmorillonite K-10 catalysed solvent-free synthesis of 2,3-disubstituted-4(3H)quinazolinones under microwave irradiation

An efficient and rapid synthesis of 2,3-disubstituted-4(3 H)quinazolinones by condensation of 2-aminobenzamide (substituted anthraniamides) with orthoesters in the presence of K-10 clay under solvent free conditions using microwave irradiation or classical heating is described.

Microwave-Assisted Efficient synthesis of Dihydro Pyrimidines: Improved High Yielding Protocol for the Biginelli Reaction

Dihydropyrimidines were synthesised in high yields by one-pot cyclocondensation reaction of aldehydes, aceto-acetates and urea using various acid catalysts like Amberlyst-15, Nafion-H, KSF clay and dry acetic acid under microwave irradiation.

Microwave-assisted efficient one-pot synthesis of nitriles in dry media

A rapid and efficient procedure is reported for the synthesis of nitriles by condensation of aldehydes with hydroxylamine hydrochloride in the presence of dibutyltin oxide supported on Al2O3 under microwave irradiation

Efficient and Practical Solvent-Free Oxidation of Alcohols using Microwave Irradiation

Alcohols are oxidised rapidly to the corresponding carbonyl compounds by montmorillonite KSF or silica supported barium manganate, under solvent-free conditions and microwave irradiation.

Conversion of Piperidine-4-ones into [1,4]-diazepan-5-ones under Microwave Irradiation Using a Silica Gel Supported NaHSO4 Catalyst

A rapid conversion of some 2,6-diarylpiperidin-4-ones into 2,7-diaryl-[1,4]-diazepan-5-ones in high yields has been developed involving treatment with hydroxylamine hydrochloride under microwave irradiation in the presence of a silica gel supported NaHSO4 catalyst.

Multistep Microwave Assisted Solvent Free Green Chemical Synthesis of 2,7-Dihydro-3H-Pyridazino[3′,4′:4,5]Indolo[3,2-c]Quinoline-3,13(12H)-Dione

A novel class of biologically active compound 2,7-dihydro-3 H-pyridazino[3′,4′:4,5]indolo[3,2- c]quinoline-3,13(12 H)-dione (10a–b)has been achieved efficiently and quickly under solvent free conditions in an open vessel microwave system. The multi step one pot synthesis involved the reaction of 8,9,10,11-tetrahydro-6 H-indolo[3,2- c]quinoline-6,7(5 H)-dione (6a–d) and glyoxylic acid monohydrate followed by cyclocondensation with hydrazine hydrate under microwave irradiation. The synthesis of 8,9,10,11-tetrahydro-6 H-indolo[3,2- c]quinoline-6,7(5 H)-dione(6a–d) has also been described from the reaction of (2-oxo-1,2-dihydroquinolin-4-yl)hydrazine with 1,3-cyclohexanedione in the absence of any solvent/catalyst/strong acid or solid support using microwaves.

Microwave-assisted routes for rapid and efficient modification of layered perovskites

Recent advances in exploiting microwave radiation in the topochemical modification of layered oxide perovskites are presented. Such methods work well for rapid bulk synthetic steps used in the production of novel inorganic-organic hybrids (protonation, grafting, intercalation, and in situ click reactions), exfoliation to produce dispersed nanosheets, and post-exfoliation processing to rapidly vary nanosheet surface groups. Compared to traditional methods that often take days, microwave methods can produce quality products in as little as 1-2 h.

Understanding MAOS through computational chemistry

Computational chemistry may explain and rationalize the impact of microwave irradiation in organic synthesis.

Hydrogen Peroxide Scavenging Activity of Novel Coumarins Synthesized Using Different Approaches

New derivatives of 7-hydroxy-4-methylcoumarin were synthesized using a chemical method and a microwave-assisted method to compare the feasibility, reaction times, and yields of the product. The newly synthesized coumarins were characterized by different spectroscopic techniques (FT-IR and NMR) and micro-elemental analysis (CHNS). In vitro antioxidant activities of these compounds were evaluated against hydrogen peroxide and were compared with standard natural antioxidant, vitamin C. Our results reveal that these compounds exhibit excellent radical scavenging activities.

Solvent-free and catalysts-free chemistry: a benign pathway to sustainability

In the past decade, alternative benign organic methodologies have become an imperative part of organic syntheses and chemical reactions. The various new and innovative sustainable organic reactions and methodologies using no solvents or catalysts and employing alternative energy inputs such as microwaves, sonication, conventional and room temperature heating conditions, mechanochemical mixing, and high-speed ball milling are discussed in detail. Environmentally benign and pharmaceutically important reactions such as multicomponent, condensation, and Michael addition reactions; ring opening of epoxides; and oxidation and other significant organic reactions are discussed. An overview of benign reactions through solvent- and catalyst-free (SF-CF) chemistry and a critical perspective on emerging synergies between SF-CF organic reactions are discussed.

Alternative energy input: mechanochemical, microwave and ultrasound-assisted organic synthesis

Microwave, ultrasound, sunlight and mechanochemical mixing can be used to augment conventional laboratory techniques. By applying these alternative means of activation, a number of chemical transformations have been achieved thereby improving many existing protocols with superior results when compared to reactions performed under traditional conditions. The purpose of this critical review is to highlight the advances in this general area by presenting such newer applications in organic synthesis (175 references).

Microwave-induced facile synthesis of water-soluble fluorogenic alginic acid derivatives

A facile microwave-induced method was developed for synthesizing water-soluble fluorescent derivatives of alginic acid (ALG) with four different diamines, hydrazine (HY), ethylenediamine (EDA), 1,6-hexanediamine (HDA), and 1,4-cyclohexanediamine (CHDA), followed by a cross-linking reaction with a natural cross linker genipin. The ethylenediamine derivative of alginic acid (ALG-EDA) exhibited good fluorescent activity, which upon cross linking was enhanced threefold. The other amide derivatives, for example, ALG-HY, ALG-HDA, and ALG-CHDA, were not fluorescent, but their respective crosslinked products exhibited excellent fluorescent activity. The fluorescence intensity had an inverse correlation with the number of carbon atoms present in the amine, which in turn was a function of degree of substitution (DS). These fluorescent polysaccharide derivatives are of potential utility in the domain of sensor applications.

Benzoylation of Amines sans Alkali: A Green Protocol in Neat Phase

A new procedure for benzoylation of aromatic and aliphatic amines has been developed in neat phase without use of any solvent or alkali.