Ultrasound activation

Jian D, Gao Q (2006) Synthesis of CdS nanocrystals and Au/CdS nanocomposites through ultrasound activation liquid-liquid two-phase approach at room temperature. Chem Eng J 121 9-16... 

Although the role of rare earth ions on the surface of TiC>2 or close to them is important from the point of electron exchange, still more important is the number of f-electrons present in the valence shell of a particular rare earth. As in case of transition metal doped semiconductor catalysts, which produce n-type WO3 semiconductor [133] or p-type NiO semiconductor [134] catalysts and affect the overall kinetics of the reaction, the rare earth ions with just less than half filled (f5 6) shell produce p-type semiconductor catalysts and with slightly more than half filled electronic configuration (f8 10) would act as n-type of semiconductor catalyst. Since the half filled (f7) state is most stable, ions with f5 6 electrons would accept electrons from the surface of TiC>2 and get reduced and rare earth ions with f8-9 electrons would tend to lose electrons to go to stabler electronic configuration of f7. The tendency of rare earths with f1 3 electrons would be to lose electrons and thus behave as n-type of semiconductor catalyst to attain completely vacant f°- shell state [135]. The valence electrons of rare earths are rather embedded deep into their inner shells (n-2), hence not available easily for chemical reactions, but the cavitational energy of ultrasound activates them to participate in the chemical reactions, therefore some of the unknown oxidation states (as Dy+4) may also be seen [136,137]. 

Activation. Erdik1 has reviewed the methods used since 1970 for activation of zinc and of organozinc reagents. Although chemical activation is still useful, ultrasound activation is being used increasingly. Thus sonic activation allows use of ordinary zinc for cyclopropanation of alkenes with CH2I2 in 67-97% yield and for Reformatsky-type reactions at room temperatures. 

MRXSOl/lipid shell + dexamethasone prodrug Ultrasound-activated drug delivery [83]... 

ImaRx/positively charged lipid sheU/plasmid DNA attached Ultrasound-activated DNA delivery [10]... 

Ultrasound activation of metals. Since its discovery as an activation technique some fifty years ago, sonication has been demonstrated to be of general use for the depassivation of different metals. In this case, the activation consists in cleaning the surface of the metal, making possible better contact between the reagents. Probably the most important applications of ultrasonic irradiation are the direct preparation of organometallic reagents and different metal-assisted reactions, for instance in aqueous media . 

As mentioned in Section HD, an important publication bearing on the question of dichlorosilane-metal reactions appeared in 198856. Boudjouk and coworkers treated t-Bu2SiX2, X = Cl, Br and I, with lithium and ultrasound activation in the presence of Et3SiH. Good yields (ca 60%) of EtjSi—SiH(Bu-t)2 were obtained in all three cases. This is rather persuasive evidence in favor of silylene formation, since Si—H bond insertion is characteristic for silylenes and it is difficult to see how the disilane could arise from the reaction of Et3SiH with a silylenoid95. 

Ultrasound activation accelerates the synthesis, probably by maintaining a clean surface on the sodium particles. This allows the Wurtz synthesis to be carried out at much lower temperature, in benzene, tetrahydrofuran (THF) or diethyl ether.14 The synthesis is also speeded by the addition of additives which complex alkali metal cations, that is 15-crown-5 ether.15... 

Ozone is the basic compound for many oxidation processes included under the general term of ozonation. In these processes, ozone may be used alone or with other agents such as hydrogen peroxide, UV radiation, catalysts, ultrasound, activated carbon, etc. In this section, information concerning the individual use of ozone is given, while its combined use with hydrogen peroxide or UV radiation is reported in later sections. 

Ultrasound activation.1 Commercial Mn02 is a weak oxidant, but can be markedly activated by ultrasonic irradiation and agitation in the case of oxidation of allylic or benzylic alcohols. 

De Lima Leite, R.H., Cognet, P., Wilhelm, A.-M. and Delmas, H. (2002) Anodic oxidation of 2,4-dihydroxybenzoic acid for wastewater treatment Study of ultrasound activation. Chem. Eng. Sci. 57, 767-778. 

The silicon-halogen, silicon-oxygen, and silicon-sulfur bonds of the haiogenosil-anes, siiyl ethers, and siiyi thioethers are cleaved by reaction with LAH, AIH3, or DIBAH, and the corresponding siiyl hydrides are obtained [CGI, CG2]. Ultrasound activation can be applied [LG2] (Figure 5.9), Anionic pentacoordinated silicon compounds are reduced to hydrogenosilanes by LAH or DIBAH [BC6]. 

For p-ketoesters, ultrasound activation [1142] of Raney nickel modified by tartaric acid 2.2 (R = H) in the presence of NaBr [578] is the method of choice (Figure... 

Bose and coworkers have reported that the condensation of ethyl biomoacetate with a variety of imines can be completed in a few hours at room temperature by means of ultrasound activation. Oxidative removal of a N-(p-methoxyphenyl) group gave )V-unsubstituted P-lactams, which are useful intermediates in the preparation of p-lactam antibiotics (Scheme 18). 

For the first of these groups, two crystalline phases Ln2(C03)3.nH20 (n = 3 n= 8), both orthorombic, have been reported [68,74,78]. Some other hydrated carbonates reported in the literature are La20(C03)2.1.4H20, which has been prepared by ultrasound activation of an aqueous solution containing urea and La(N03)3 [71], and a neodymium peroxycarbonate, Nd202(C03)2-2H20 [79],... 

The Suzuki-Miyaura cross-coupling reaction is a standard method for carbon-carbon bond formation between an aryl halide or triflate and a boronic acid derivative, catalyzed by a palladium-metal complex. As with the Mizoroki-Heck reaction, this cross-coupling reaction has been developed in ionic liquids in order to recycle and reuse the catalyst. In 2000, the first cross-coupling of a halide derivative with phenylboronic acid in [bmim] [BF4] was described. As expected, the reaction proceeded much faster with bromobenzene and iodobenzene, whereas almost no biphenyl 91 was obtained using the chloride derivative (Scheme 36). The ionic liquid allowed the reactivity to be increased, with a turnover number between 72 and 78. Furthermore, the catalyst could be reused repeatedly without loss of activity, even when the reaction was performed under air. Cross-coupling with chlorobenzene was later achieved - although with only a moderate yield (42%) - using ultrasound activation. 

The simulation of sonochemical effects on liquid-solid reactions is accomplished by a two-center model that allows for mechanically activated areas on a solid with increased reactivity. The parameters have been fitted to experiments and can be used to find suitable reaction parameters as well as a prediction whether or not a given Grignard reaction will perform better under ultrasound activation or not. 

Hydrodynamic-pressure-activated ° Hydration-activated o Vapor-pressure-activated ° Mechanically activated ° Magnetically activated ° Ultrasound-activated ° Electrically activated... 

Biocatalysis could be employed to aid the formation of indolizine derivatives in an aqueous medium, as seen in Figure 16. Ultrasound activation was compared to conventional heating, affording 7,7 -bis-indolizines with similar yields in much shorter reaction times [31]. 

D32/005/04 Microwave and Ultrasound Activation in Chemical Analysis) for the financial support. Also L. Vidal and C.E. Domini gratefully thank the University of Alicante, Spain (Vicerrectorado de Relaciones Institudonales y Cooperacion and Vicerrectorado de Investigacion, Desarrollo e Irmovacion) for their grants. 

Previous works have shown that metallic iodide activated bismuth(lll) chloride efficiently catalyzes the Mukaiyama aldol and Michael reactions. Moreover, it has been shown that ultrasound activates significantly the catalytic power of these metallic halide systems [32a]. Interestingly, the use of these catalytic systems proved to be particularly remarkable in the case of the synthesis of functional furan derivatives [24c, 32b]. The use of Bi(OTf)3 xH20 has also been reported for these reactions [32c-e]. The Mukaiyama aldol reaction in an ionic liquid such as [Bmim][BF4] proceeds smoothly with silyl enolates and a catalytic amount of Bi(0Tf)3 %H20 [32d,e]. Various silyl enolates and aldehydes were tested. Moderate to very good yields of P-hydroxy ketones were obtained. 

Harada Yo., Ogawa, K., Me Yu., Endo, H., Peril Jr. L.B., Uemura, X, Tachibana, K. Ultrasound activation of Ti02 in melanoma tumors. Journal of Controlled Release, 2011,149,190-195. 

---