New activation methods used in green chemistry for the synthesis of high added value molecules (original) (raw)
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ChemInform, 2010
Various emerging ''greener'' strategic pathways, researched primarily in the author's own laboratory, are summarized. They include solvent-free mechanochemical methods that involve the use of hypervalent iodine reagents at room temperature for the synthesis of heterocyclic entities, and useful conversion of ketones into b-keto sulfones and their a-tosyloxy derivatives in high yields. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports, such as alumina, silica, clay, or ''doped'' surfaces, is described; it is applicable to a wide range of cleavage, condensation, cyclization, rearrangement, oxidation, and reduction reactions, including rapid one-pot assembly of heterocyclic compounds from in situ generated reactive intermediates. The strategy is adaptable to multi-component reactions, e.g. Ugi and Biginelli reactions, for rapid assembly of a library of compounds. Synthesis of a wide variety of significant precursors and intermediates, namely enones, imines, enamines, nitroalkenes, and oxidized sulfur species, is possible and their value in concise MW synthesis of 2-aroylbenzofurans and thiazole derivatives is illustrated. Ultrasound-and MW-assisted solventless preparation of ionic liquids and their application in alkylation and metal-catalyzed multi-component reactions are described. With a view to consume greenhouse gas, carbon dioxide (CO 2), efficient reaction of epoxides with CO 2 provides ready access to cyclic carbonates using only a catalytic amount of recyclable indium-based ionic liquid. MW heating in aqueous reaction media enables expeditious N-alkylation reactions of amines and hydrazines to afford a series of heterocyclic ring systems, such as N-azacycloalkanes, 4,5-dihydropyrazoles, and pyrazolidines. A general and expeditious MW-enhanced nucleophilic substitution approach uses easily accessible starting materials such as halides or tosylates in reaction with alkali azides, thiocyanates, or sulfinates in the absence of any phase transfer catalyst to produce azides, thiocyanates, and sulfones, respectively, wherein a variety of reactive functional groups are tolerated. A three-component condensation (MCC) approach for the synthesis of useful 2-amino-2-chromenes is described using a recyclable nanosized magnesium oxide catalyst in aqueous poly (ethylene glycol) (PEG) medium at room temperature. A general greener approach to shape-selective generation of nanomaterials is summarized including their potential application as nanocomposites.
Green revolution in chemistry by microwave assisted synthesis A review
Green chemistry efficiently utilizes raw materials (preferably renewable), eliminates waste, and avoids the use of toxic or hazardous reagents and solvents in the manufacture and application of chemical products. Microwave assisted technique opens up new opportunities to the synthetic chemist in the form of new reactions that are not feasible using conventional heating and serve a flexible platform for chemical reactions. Over the past five years there has been a dramatic uptake in the use of microwaves as an energy source to promote synthetic transformations. Microwave-assisted synthesis (MAOS) is clearly a method by which the laboratory chemist can achieve goals in a fraction of the time as compared to traditional conductive heating methods. Reaction times in the best cases have been reduced from hours or days to minutes. The basic mechanisms observed in microwave assisted synthesis are dipolar polarization and conduction. The technique offers a simple, clean, fast, efficient, and economic way for the synthesis of a large number of molecules, providing the momentum for many chemists to switch from traditional heating methods to microwave assisted chemistry. In the present article an attempt was made to focus on what is microwave assisted synthesis, how is it generated and what importance may it have.
Alternative energy input: mechanochemical, microwave and ultrasound-assisted organic synthesis
Chemical Society Reviews, 2012
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).
Practical Approach to Green Chemistry
International Journal of Pharmacy and Pharmaceutical Sciences, 2017
Objective: The basic principles of green chemistry addresses various issues related to synthesis of chemical compounds: planning organic synthesis to maximise yield, prevention/minimization of waste, atom economy, the use of less lethal chemicals, use of safer solvents, renewable starting materials, energy efficiency and use of green catalysts. The objective of this study is to elaborate the practical approach of green methods.Methods: In this paper, we elucidate some important common syntheses having green procedures which can be used in the fields of pharmaceutical chemistry and other fields as well.Results: Green chemistry principles follow up to reduce pollution and environmental degradation by utilizing eco-friendly, non-hazardous, reproducible and efficient solvents and catalysts in the synthesis of drug molecules, drug intermediates and in researches involving synthetic chemistry. The paper also approaches green methods in which microwave radiation can be used as an energy ef...
Microwave Synthesis-A Potential Tool for Green Chemistry
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Microwave radiation, an electromagnetic radiation, is widely use as a source of heating in organic synthesis. The basic mechanisms observed in microwave assisted synthesis are dipolar polarization and conduction. Microwave assisted organic synthesis (MAOS) has emerged as a new "lead" in organic synthesis. The technique offers simple, clean, fast, efficient, and economic for the synthesis of a large number of organic molecules, have provided the momentum for many chemists to switch from traditional heating method to microwave assisted chemistry. In the recent year microwave assisted organic reaction has emerged as new tool in organic synthesis. In the present article an attempt was made to focus on what is microwave, how is it generated and what importance may it have.
Synthesis of chemicals with pharmaceutical interest using green technologies
2016
Preservation of the environment is a very present theme in our current lifes. The pharmaceutical and chemical companies are normally seen as threatening to several ecosystems and the beings that reside in them, by fabricating their products unsustainably and polluting the surrounding environment. Yet, there is more than it looks to this, since when the concepts of green chemistry are applied, they become part of the solution, instead of part of the problem. The Sun is the main source of energy for planet Earth, by being capable of supplying, in just one day, the global energetic necessities of 27 years. Since the contemporary energetic need is extremely high, it is favorable to choose this clean and infinite source over non-renewable sources. One way of exploring this energetic spring is through the use of light to activate chemical processes. Heterogeneous photocatalysis consists on the promotion of chemical processes, using materials known as photocatalysts, which are materials wi...
Microwave Assisted Green Synthesis
International Journal of Scientific Research in Science and Technology, 2020
Chemistry has brought about revolution in each field of life whether it is medical field, agricultural field or any other, its impact can be seen everywhere. But the hazardous waste by product so formed and in order to get rid of it, finally marked the beginning of Green Chemistry. The reason why Microwave assisted organic reaction in organic chemistry is getting more popular because it provide better yield, less consumption of energy and cost effective . Altogether it make greener/cleaner chemistry having feature of sustainability in it. . Microwave organic synthesis opens up new opportunities to the synthetic chemist in the form of new reaction that are not possible or if possible take more time by conventional heating and serve a flexible platform for chemical reaction. Microwave heating is playing a vital role in treatment of various kinds of waste like domestic and hazardous nuclear and industrial wastes. Microwave heating can be advantageously used for waste management in areas where human exposure can cause invariable health issues. Altogether it can be justified by saying that microwave is a convenient way towards achieving the goal of green/sustainable chemistry, and is highly recommended to use in organic preparations for various purposes including Pharmaceutical chemistry.
A Focus & Review on the Advancement of Green Chemistry
Green chemistry which is the latest and one of the most researched topics now days has been in demand since 1990's. Majority of research in green chemistry aims to reduce the energy consumption required for the production of desired product whether it may be any drug, dyes and other chemical compounds. It aims to reduce or even eliminates the production of any harmful bi-products and maximizing the desired product without compromising with the environment. The three key developments in green chemistry include use of super critical carbon di oxide as green solvent, aqueous hydrogen peroxide as an oxidizing agent and use of hydrogen in asymmetric synthesis. It also focuses on replacing traditional methods of heating with that of modern methods of heating like microwave radiations so that carbon footprint should be reduces as low as possible. This review emphasize on principle, methodology and recent applications of green chemistry.