Ultrasound irradiation

Modem technology has influenced these reactions. Ultrasound assisted versions of these reactions has been reported. Ultrasound irradiation facilitated the Diels-Alder reaction of dimethylhydrazone 94 with 95. The resultant pyridine 96 are afforded in shorter reaction times and increased yields. 

Ultrasound irradiation is particularly beneficial for Diels Alder reactions of unactivated azadienes because the reaction can be carried out under mild conditions. 

Spanish researchers [32] also noted a considerable improvement upon sonica-tion of Diels-Alder reactions of l-dimethylamino-3-methyl-l-azadiene 44 with a variety of electron-deficient dienophiles by using diene as solvent or in acetonitrile (Scheme 4.9). Ultrasound irradiation which allows mild reaction conditions gave good to excellent yields. 

Bimetallic Au/Pd nanoparticles were prepared by ultrasound irradiation of a mixture solution of NaAuCl4-H20/PdCl2 2NaCl-3H20 by which the Au and Pd ions were reduced to the metallic state. The Mossbauer spectra of AuPd-SDS particles, with SDS (sodium dodecyl sulfate) representing the surfactant of the system, consist of two components, one for the pure Au core and the other for the alloy layer at the interface of Au core and Pd shell [435]. 

Ultrasound irradiation —> temperature increase —> release of drug... 

Figure 1 Time-dependent composition data is shown for the hydrogenation of aqueous 3-buten-2-ol for both (a) ultrasound irradiated and (b) magnetically stirred systems. The symbols correspond to experimental measurements (3-buten-2-ol 3BEN20L-solid circles 3-buten-2-one 3BEN20NE-open hourglass 2-butanone 2BONE-open triangles 2-butanol 2BOL-crossed squares). The lines in the ultrasound experiment simply connect the data points, whereas for the stirred experiment the lines correspond to a modeled fit (see text).

Peng Y, Song G (2001) Simultaneous microwave and ultrasound irradiation A rapid synthesis of hydrazides. Green Chem 3 302-304... 

Fig. 5.1 One example of the irradiation set-up and the characteristic of the reaction vessel a standing-wave type ultrasound irradiation system [29]...

The sonochemical reduction of Au(III) has been investigated under Ar in the presence of 20 mM 1-propanol at different frequencies, where two types of ultrasound irradiation systems were used one is a horn type sonicator (Branson 450-D, frequency 20 kHz, diameter of Ti tip 19 mm) and the other is a standing wave sonication system with a series of transducers operating at different ultrasound frequencies (L-3 Communication ELAK Nautik GmbH, frequency 213, 358, 647, and 1,062 kHz, diameter of oscillator 55mm) [33]. All experiments were performed at a constant ultrasound intensity ((0.1+/—0.01 W mL-1), which was determined by calorimetry. 

Sathish Kumar et al. [45] prepared bimetallic Au-Ru nanoparticles by the simultaneous reduction of both Au3+ and Ru3+ ions by ultrasound irradiation at three different molar ratios (Au3+ Ru3+ 1 1, 1 3 and 1 5) in 4 h in the presence of PEG. A significant change in the absorption as a function of sonication time was observed for Au-Ru bimetallic particles (Fig. 6.10), which indicated the... 

Self-assembled nanorods of vanadium oxide bundles were synthesized by treating bulk V2O5 with high intensity ultrasound [34]. By prolonging the duration of ultrasound irradiation, uniform, well defined shapes and surface structures and smaller size of nanorod vanadium oxide bundles were obtained. Three steps which occur in sequence have been proposed for the self-assembly of nanorods into bundles (1) Formation of V2O5 nuclei due to the ultrasound induced dissolution and a further oriented attachment causes the formation of nanorods (2) Side-by-side attachment of individual nanorods to assemble into nanorods (3) Instability of the self-assembled V2O5 nanorod bundles lead to the formation of V2O5 primary nanoparticles. It is also believed that such nanorods are more active for n-butane oxidation. 

Pol VG, Palchik O, Gedanken A, Felner I (2002) Synthesis of europium oxide nanorods by ultrasound irradiation. J Phys Chem B 106(38) 9737-9743... 

Gold sulphide had a featureless non-crystalline plain surface with very sharp and smooth edges of the dried mass. However, the smoothness of the surface was destroyed completely with blisters appearing as a result of cavitation, after 30 min of ultrasound irradiation. A closer look at the surface at x 7,500 magnification reveals extensive surface erosion as a result of the micro-jets streaming. 

Pol VG, Grisaru H, Gedanken A (2005) Coating noble metal nanocrystals (Ag, Au, Pd and Pt) on polystyrene spheres via ultrasound irradiation. Langmuir 21 3635-3640... 

Liang J, Komarov S, Hayashi N, Kasai E (2007) Recent trends in the decomposition of chlorinated aromatic hydrocarbons by ultrasound irradiation and Fenton s reagent. J Mat Cycles Waste Manage 9(1) 47—55... 

The use of ultrasound in both the synthesis and crystallisation of a broad array of both organic and inorganic materials has been intensively researched and is well documented [61-64]. An application of ultrasound that has received relatively less attention however, is in the dissolution of colloidal particles. Prakash and Ghosh [65] reported on the dissolution of silver colloids under 1 MHz ultrasound irradiation, proposing that the silver is oxidised by sonochemically produced hydroxyl radicals. Sostaric et al. [66] investigated the dissolution of MnC>2 colloids in the presence of aliphatic alcohols at a lower frequency of 20 kHz. They found that... 

Brotchie A, Ashokkumar M, Zhang XFI (2010) Behaviour of interfacial nanofluids under ultrasound irradiation. Manuscript under review... 

The reaction temperature should be kept below 20°C to prevent side reactions. If the temperature exceeds 20°C, one should stop both the addition of the prenyl chloride and the ultrasound irradiation, and wait for the reaction temperature to fall below 15°C. 

Direct thionation of amino acid derivatives has been achieved using P4S10. Direct thionation of anilide has been achieved with a mixture of P4S10 and anhydrous Na2C03 in THF.19 Selective thionation of amide has been achieved using P4S10 in THF under ultrasound irradiation. By-product is absent from the phosphorus pentasulfide thionation. Thionation of the amide with Lawesson s reagent is less selective (Scheme 4).20... 

Ultrasound irradiation of mixtures of amines RNH2 (R = PI1CH2, Ph or Ar) and methyl pyruvate results in the 3-pyrrolin-2-ones 322377. The silver tetrafluoroborate-catalysed cyclization of the allenic amines 323 leads either to a pyrroline 324 or tetrahydropyridine 325, depending on the structure of the amine. The former is formed from 323 (R = H), the latter from 323 (R = Me)378. 

Gedanken and colleagues136 investigated the Diels-Alder reactions of trichloromethyl allenyl sulfoxides 203 and cyclopentadiene under ultrasound irradiation. Allenes 203 are generally very sluggish in reactivity. However, when ultrasound was applied, the reactions of allenes 203 with cyclopentadiene were completed within 2 hours (equation 57). Mixtures of endo (204) and exo (205) isomers were obtained in all instances. When the y-position of the allenyl sulfoxides was substituted, additional mixtures of E and Z isomers were obtained. 

Chemical/Physical. Ultrasonic irradiation (205-1078 kHz) of methyl tert-butyl ether (100 mM) in water in the presence of ozone maintained at 23 °C yielded tert-butyl formate and tert-butyl alcohol (Kang et al., 1999). The highest reaction rates occurred at 358 and 618 kHz. The combination of ozone and ultrasonic irradiation was more effective in degrading methyl tert-butyl ether than ultrasound and ozone alone. The investigators concluded that the combination of ozone and ultrasound irradiation was most effective at a frequency of 358 kHz. The rate of degradation of methyl tert-hniyX ether was not affected in the presence of natural organic matter. 

I 75 Catalytic Properties of Soluble Iridium Nanoparticles NaBH4, surfactant, ultrasound irradiation... 

It is now widely recognized that microbubbles can be destroyed by ultrasound irradiation [70]. This may be explained simply by the fact that when microbubbles are subjected to external pressure, they shrink and gas leaks out and dis-... 

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