Microwave-assisted organic synthesis domestic ovens

Although many of the early experiments in microwave-assisted organic synthesis have been carried out in domestic microwave ovens, the current trend clearly is to use specialized instruments for this type of chemical synthesis. Experiments carried out in domestic ovens have been found to be difficult to reproduce, owing to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distributions, and the unpredictable formation of hotspots. 

As was mentioned previously, pressurized conditions have been reported for microwave-assisted organic synthesis [50], The reactions were carried out at a domestic microwave oven and commercially available screw-up pressure vessels made of Teflon, PET and PEEK, which are both microwave transparent (Fig. 5.1). It has to be pointed out that reactions under such conditions have to be strictly controlled with an efficient power feed-... 

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. 

Several microwave-assisted protocols for soluble polymer-supported syntheses have been described. Among the first examples of so-called liquid-phase synthesis were aqueous Suzuki couplings. Schotten and coworkers presented the use of polyethylene glycol (PEG)-bound aryl halides and sulfonates in these palladium-catalyzed cross-couplings [70]. The authors demonstrated that no additional phase-transfer catalyst (PTC) is needed when the PEG-bound electrophiles are coupled with appropriate aryl boronic acids. The polymer-bound substrates were coupled with 1.2 equivalents of the boronic acids in water under short-term microwave irradiation in sealed vessels in a domestic microwave oven (Scheme 7.62). Work-up involved precipitation of the polymer-bound biaryl from a suitable organic solvent with diethyl ether. Water and insoluble impurities need to be removed prior to precipitation in order to achieve high recoveries of the products. 

Other microwave-assisted parallel processes, for example, involving solid-phase organic synthesis (SPOS) have already been discussed in Sect. 12.2. (Schs. 12.6, 12.7, and 12.10). In the majority of cases described so far, however, domestic multimode microwave ovens have been used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irra-... 

In the literature, first microwave-assisted experiments on organic synthesis employed multimode household microwave ovens [12,13]. More recently, the use of microwave reactors for chemical syntheses has become more advanced, and, at the moment, some chemical journals specializing in organic chemistry intend to refuse manuscripts in which experiments were carried out in a domestic microwave oven (even including ovens with... 

A new facile method for the rapid synthesis of aliphatic polyamides and polyimides was developed by using a domestic microwave oven to facilitate the polycondensation of both w-amino acids and nylon salts as well as of the salt monomers composed of aliphatic diamines and pyromellitic acid or its diethyl ester in the presence of a small amount of a polar organic medium. Suitable organic media for the polyamide synthesis were tetramethylene sulfone, amide-type solvents such as A -cyclohexyl-2-pyrrolidone (CHP) and 13-dimethyl-2-imidazolidone (DMI), and phenolic solvents like m-cresol and c)-chlorophenol, and for the polyimide synthesis amide-type solvents such as A-methyl-2-pyrrolidone, CHP, and DMI. In the case of the polyamide synthesis, the polycondensation was almost complete within 5 min, producing a series of polyamides with inherent viscosities around 0.5 dL/g, whereas the polyimides having the viscosity values above 0.5 dL/g were obtained quite rapidly by the microwave-assisted polycondensation for only 2 min. 

Karuehanon et al. (2012) reported the microwave-assisted S Ar reaction of 2,4,6-trichloro-l,3,5-triazine with various unprotected amino acids for the synthesis of Cj-symmetrical polycarboxylate ligand. These products can be used as structural directing units in metal-organic frameworks. A domestic microwave oven was used as the heating device and the reactions were performed in water. Comparison between the reactions performed under conventional heating and microwave irradiation was made. It was observed that the microwave method takes 20 minutes less time to afford the desired ligands than the conventional method. 

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