Ultrasound and Microwave Irradiation

The application of ultrasonic irradiation in reactions using heterogeneous catalyst is a promising technique. The advantages of ultrasound procedures, such as good yields, short reaction times, and mild reaction conditions, are well documented. Ultrasonic irradiation can also be used to influence (06CHC172,09MI708). 

Patil et al. found that the Pechmann reaction coifld be carried out using ultrasonic irradiation in the presence of BiCl3, as a Lewis acid catalyst 

Gutierrez-Sanchez et al. synthesized an important insecticide intermediate, namely, hymecromone from the condensation of resorcinol and EAA at moderate temperatures in low yield. However, in solvent-free conditions under ultrasound irradiation and in the presence of zeolites the desired product has been obtained in higher yield, required shorter reaction time, and naturally more environmental friendly conditions with nearly 100% selectivity (09MI318). 

The preparation of coumarin derivatives in the presence of H2SO4 under MWI (200W) and H2SO4 in comparison with classical methods indicated higher yields 68-82% as well as significant shorter reaction times (97JCR(S)58). 

The synthesis of coumarins in the presence of catalytic amounts of concentrated H2SO4 under MWI for 15—40 s was described by F. A. Chattha et al. (08MI94). It produces less side products, which reduces contamination threats and gives better yields of the desired products. 

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Use of combination of cavitation and advanced oxidation processes such as ozonation, chemical oxidation using hydrogen peroxide and photocatalytic oxidation and use of combination of ultrasound and microwave irradiations. 

Other new methods used in heterogeneous catalytic reactions include the use of ionic liquids as catalysts and simultaneous applications of ultrasound and microwave irradiation. An ionic liquid as an acidic catalyst has been used for synthesis of cou-marins [78], in esterification of acetic acid with benzyl alcohol [79], in catalytic esterification at room temperature [80], in alkylation of a-methylnaphthalene with long-chain alkenes [81], and in hydrogenation of benzene [82]. 

Use of electromagnetic and acoustic irradiation to enhance heterogeneous catalytic reactions has been recently reviewed [83]. Alternative use of ultrasound and microwave irradiation for hydrocarbon oxidation and catalyst preparation, to improve selectivity, was also recently reported [84]. 

In recent years, ultrasound and microwave irradiation have been extensively used to synthesize some materials with unusual properties. Ultrasound irradiation can... 

Ultrasound and microwave irradiation processes are known as excellent methods for the preparation of nanoparticles. Recently, nanoparticles of rare earth (Y, La, Ce, Sm, Eu, and Er) oxides have been synthesized [77-81]. In these cases, rare earth nitrates were used as starting materials. When sodium dodecyl sulfate (SDS) was added as a templating agent, layered and hexagonal mesostructures of high specific surface area (225-250 m g ) can be obtained [77]. Monodispersed Ce02 nanoparticles with a mean particle of ca. 3 nm are obtained when tetrametylammonium hydroxide [78] or polyethylene glycol [79, 80] are used as the additives. In addtion, europium oxide nanorods are obtained by the sonication of an aqueous solution of europium nitrate in the presence of anunonia [81]. The particle sizes were about 50 x 500 nm (IF x L) as described in Fig. 6-9. 

Cravotto G, Garella D, Calcio Gaudino E, Turci F, Bertarione S, Agostini G, Cesano F, Scarano D (2011) Rapid purification/oxidation of multi-walled carbon nanotubes undo-300 kHz-ultrasound and microwave irradiation. New J Chem 35 915-919... 

Additionally, Mizoroki-Heck reactions were carried out at very low ligand loading or ligand-free with s/c of up to 1.0 x lO" (Pd/C, or Pd(OAc)2) under simultaneous ultrasound and microwave irradiation. The reactions result in excellent yields. 4-Iodostyrene, 4-bromoanisole, or 4-bromoacetophenone can be coupled in presence of a cocatalyst (e.g. Wilkinson catalyst, 0.001-0.005%). Under full conversion, the stilbenes could be synthesized in up to 99% yield with an E/Z ratio of 5 1 to 16 1 (Scheme 15.16 [195]). 

Impressive and elegant replacement of sulfuric acid with the wide variety of heterogenous, homogenous, and nanocatalysts besides the use of ultrasound and microwave irradiation instead of conventional heating have been investigated, well documented, and showcased in this article. These precedents, which demonstrate nicely and clearly the efficient and facile synthesis of coumarins via Pechmaim reaaion should continue to stimulate the interests and attract the attention of synthetic organic chemists. 

A. Barge, S. Fuzerooa, D. Upadhaya, D. GareUa, S. Aime, L. Tei, G. Cravotto, A new, easy access to the 6-aminoperhydro-l,4-diazepine scaffold under ultrasound and microwave irradiation. Synthesis (2008) 1879. 

Well-defined flower-like CdS nanostructures have been synthesized by Tai and Guo (2008) under ultrasound and microwave irradiations, simultaneously. Hexagonal nanopyramids and/or nanoplates were obtained depending on different sulfur sources. The synergistic effect of microwave and sonochemistiy has been proposed for the formation of these nanoflowers. They show a large bine-shift npto 100 nm as compared to simple low-dimensional CdS nanostmctnres. This stmctnre induced shift in optical properties, which may find some potential applications in optoelectronics devices, catalysis, and solar cells. 

In the main, the original extractive alkylation procedures of the late 1960s, which used stoichiometric amounts of the quaternary ammonium salt, have now been superseded by solid-liquid phase-transfer catalytic processes [e.g. 9-13]. Combined soliddiquid phase-transfer catalysis and microwave irradiation [e.g. 14-17], or ultrasound [13], reduces reaction times while retaining the high yields. Polymer-supported catalysts have also been used [e.g. 18] and it has been noted that not only are such reactions slower but the order in which the reagents are added is important in order to promote diffusion into the polymer. 

Both ultrasound and microwave have been applied to accelerate the reaction the Jourdan-Ullmann condensation under microwave irradiation can be carried out in... 

Safari et al. [45] successfully demonstrated for the first time that Cu powder and ultrasound 300 W/H2O could be used as an excellent and efficient catalyst for convenient synthesis of 2,3-dihydroquinazohn-4(l//)-one derivatives under solvent-free conditions and microwave irradiation (Scheme 13.8). The protocol proves to be efficient and environmentally benign in terms of easy workup, high yields, and ease of recovery of catalyst. In addition, the present method is superior in terms of green media, the amorrrrt of catalyst, and reaction time. 

Additionally, they have examined the Knoevenagel-Doebner reaction in the aqueous media under simultaneous irradiation and observed to be greatly benefited [46]. Cravotto and Cintas have reviewed recently the combined use of ultrasound and microwave heating in the process chemistry [47]. 

As with 16-38, these reactions have sometimes been performed with acid catalysts. Ultrasound has been used to promote the reaction, and it has also been done without solvent using microwave irradiation. Another solid-state variation is done on moist LiBr. Zeolites have been used to promote the... 

Wu et al. [12] used both microwave (MW) and ultrasound (US) methods individually and in combination to examine the combined effect. The rapid thermal effect of MW could be seen on polar chemicals and more OH radicals were produced due to US. Microwave irradiations have shown enhanced degradation effect when applied with sonication in absence of additional catalyst though the rate increased more in presence of H2O2. The rate order was found to be MW-US > MW > US. 

Sydnones 78 (R1 = Ph, Ar or 3-pyridyl, R3 = H or Me) are obtained from the nitrosoamino acids 77 and acetic anhydride under ultrasound (94MI153). Three examples of the formation of oxadiazoles by microwave irradiation are from O-acyl amide oximes 79 in the presence of aluminium oxide, from amide oximes 80 and isoprop-enyl acetate in the presence of KSF-clay and from N,N -diacylhydrazines 81 and thionyl chloride (95SC1451). 

The irradiation of the solution containing metal ions with ultraviolet or visible light, and microwave and ultrasound irradiation (Rocha et al., 2007). 

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