Microwave-assisted organic synthesis solvents

In modern microwave synthesis, a variety of different processing techniques can be utilized, aided by the availability of diverse types of dedicated microwave reactors. While in the past much interest was focused on, for example, solvent-free reactions under open-vessel conditions [1], it appears that nowadays most of the published examples in the area of controlled microwave-assisted organic synthesis (MAOS) involve the use of organic solvents under sealed-vessel conditions [2] (see Chapters 6 and 7). Despite this fact, a brief summary of alternative processing techniques is presented in the following sections. 

High-temperature Water as a Medium or Solvent for Microwave-assisted Organic Synthesis I 51... 

The appropriateness of using of microwave-assisted organic synthesis to obtain pyridinecarboxylic acids and pyrimidinecarboxylic acids was also described in [202]. The application of microwave irradiation reduces significantly the reaction time from 2 h to 10 min, increases yields of the target compounds and also allows high-boiling and hard-to-remove solvents (DMF and acetic acid) to be replaced by ethanol. 

Modified microwave ovens. The accuracy and safety factor in microwave assisted organic synthesis can be increased by causing a slight variation in domestic microwave oven. The modified microwave oven differs from domestic microwave oven in having a hole on top of cavity. This allows the introduction of a tube (acting as an air cooler) surmounted by a water cooler to maintain reaction s solvent reflux or under inert atmosphere, or allowing the chemist to follow multistep procedures of chemical synthesis. 

From the foregoing discussion, the technology for microwave-assisted organic synthesis with organic solvents (under pressure if necessary) is now employed extensively and routinely in chemical discovery, organic synthesis, and medicinal chemistry [16, 17]. Microwave reactors have found niche applications in the production of intermediates, flavors and fragrances, specialty chemicals, and pilot-scale manufacture. Units capable of parallel or sequential operation, some of which may be operated robotically and remotely, are employed around the clock in industrial chemical discovery. 

Microwave energy is a key enabling technology in achieving the objective of sustainable (green) chemistry. It has been shown that solvent-free conditions are especially suited to microwave-assisted organic synthesis, because reactions can be run... 

The development of modem and reliable procedures for microwave-assisted organic synthesis has also been used advantageously for 1,2,4-oxadiazole synthesis by avoiding time-consuming steps, using green solvents or solvent-free conditions, or by directly employing acids rather... 

Superheated (subcritical) water as solvent in microwave-assisted organic synthesis of compounds of valuable pharmaceutical interest 13COC 1158. 

This timescale of these microwave-assisted reactions is in minutes and it enables a facile and rapid scoping of reaction conditions, for example, time, temperature, reagents and solvents. This rapid optimization can be used to rapidly identify routes for the synthesis of novel chemical entities. Microwave-assisted organic synthesis is no longer a curiosity now, it is a rapidly growing technology, but it has not been used with full potential. 

Microwave technology—chemical synthesis applications, 16 538-594 microwave-accelerated solvent-free organic reactions, 16 555-584 microwave-assisted organic reactions in the liquid phase, 16 540-555 Microwave technology, 16 509-537. See also Microwave power Microwave technology— chemical synthesis applications... 

A new microwave reactor for batchwise organic synthesis is described in Ref. 712 (Fig. 3.5). Its use permits us to carry out synthetic works or kinetic studies on the 20 100 m L scale, with upper operating limits of 260°C and 10 MPa (100 atm). Microwave-assisted organic reactions can be conducted safely and conveniently, for lengthy periods when required, and in volatile organic solvents. The use of water as a solvent is also explored [712]. 

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