749 Acta Chim. Slov. 2009, 56, 749–764 Gupta et al.: General Characteristics and Applications ... Review General Characteristics and Applications of Microwaves in Organic Synthesis Monika Gupta,* Satya Paul and Rajive Gupta Department of Chemistry, University of Jammu, Jammu 180006 * Corresponding author: E-mail: monika.gupta77@indiatimes.com; Received: 02-12-2008 Abstract This review focusses upon the key achievements made in organic synthesis using microwave-assisted reactions in the solid phase, with neat reactants and under solvent-free conditions. It also highlights the general characteristics of microwave applications in organic synthesis. It shows that reactions under microwaves are fast, with often in- creased reaction rates and lead to better selectivity. Some of the microwave-assisted reactions can even be carried out under neat conditions therefore leading to the area of green chemistry. Keywords: Microwaves, green chemistry, activation, solid phase, neat, solvent-free, alkylation, heterocycles 1. Introduction In the context of green chemistry, among the non- conventional methods of reaction activation in organic synthesis, microwave irradiation for reaction activation provides an alternative to the conventional heating for in- troducing energy into chemical reactions by using the abi- lity of some liquids and solids to transform electromagne- tic energy into heat. This in situ mode of heat generation has attracted many chemists because its magnitude de- pends on the dielectric properties of the molecules. The microwave-assisted reactions are fast, clean, economic and eco-friendly and this technique has been proposed as the “technology of tomorrow”. 2. Advent of Microwaves The magnetron, 1 a remarkable device for generating fixed-frequency microwaves, was designed by Randall and Booth at the University of Birmingham. A magnetron is a vacuum device which converts DC electrical energy into microwaves. In early days, it was recognized that microwaves could heat water in a dramatic fashion. Domestic and commercial appliances for heating and cooking of foods began to appear in the 1950s. In 1947, the appliance called “Radarange” appeared on the market; it was intended for food processing. The first microwave oven was introduced by Tappan in 1955 but the widespread use of domestic mi- crowave ovens occurred during the 1970s and 1980s. The first application of microwave irradiation in chemical synthesis was published in 1986. 2 3. Microwaves in Organic Synthesis Microwaves have been used to speed up chemical reactions in the laboratory, 3 which led scientists to investi- gate the mechanism of microwave dielectric heating and to identify the advantages of the technique for chemical synthesis. 4 During recent years, microwaves have been extensi- vely used for carrying out chemical reactions and have be- come a useful non-conventional energy source for perfor- ming organic synthesis. 5 This is supported by a great number of publications in recent years, particularly in 2003, related to the application of microwaves as a conse- quence of a great availability of dedicated and reliable mi- crowave instrumentation. 6–9 The first recorded application of microwave (MW) energy in organic synthesis is the aqueous emulsion poly- merization of butyl acrylate, acrylic acid and methacrylic acid using pulsed electromagnetic radiation. 10 The start of the rapid growth of microwave-assisted procedures in or- ganic synthesis was ignited in 1986 by pioneering papers