Ultrasound sonochemistry

The chemical applications of ultrasound (Sonochemistry) have become an exciting new field of research during the past decade. Recently, Li and coworkers have found an efficient and convenient procedure for the preparation of oximes via the condensation of aldehydes and ketones in ethanol with hydroxylamine hydrochloride under ultrasound irradiation (Scheme 8). Compared with conventional methods, the main advantages of the sonochemical procedure are milder conditions, higher yields and shorter reaction periods. The reason may be the phenomenon of cavitations produced by ultrasound. 

Chen, D., Sharma, S.K., Mudhoo, A. (eds.) Handbook on Applications of Ultrasound Sonochemistry for Sustainability. CRC Press, Boca Raton (2012)... 

D. Chen, S.K. Sharma, A. Mudhoo (eds.), Handbook on applications of ultrasound sonochemistry for sustainability (CRC Press, 2011)... 

Mason T J and Lorimer J P 1998 Sonochemistry Theory, Applications and Uses of Ultrasound In Chemistry (Chichester Ellis Florwood)... 

Birkin P R and SilvaMartinez S 1997 A study on the effects of ultrasound on electrochemical phenomena Ultrasonics Sonochemistry 4 121... 

The chemical effects of ultrasound do not arise from a direct interaction with molecular species. Ultrasound spans the frequencies of roughly 15 kH2 to 1 GH2. With sound velocities in Hquids typically about 1500 m/s, acoustic wavelengths range from roughly 10 to lO " cm. These are not molecular dimensions. Consequently, no direct coupling of the acoustic field with chemical species on a molecular level can account for sonochemistry or sonoluminescence. 

Homogeneous sonochemistry typically is not a very energy efficient process (although it can be mote efficient than photochemistry), whereas heterogeneous sonochemistry is several orders of magnitude better. Unlike photochemistry, whose energy inefficiency is inherent in the production of photons, ultrasound can be produced with neatly perfect efficiency from electric power. A primary limitation of sonochemistry remains the small fraction... 

Sonochemistry is strongly affected by a variety of external variables, including acoustic frequency, acoustic intensity, bulk temperature, static pressure, ambient gas, and solvent (47). These are the important parameters which need consideration in the effective appHcation of ultrasound to chemical reactions. The origin of these influences is easily understood in terms of the hot-spot mechanism of sonochemistry. 

Homogeneous Sonochemistry Bond Breaking and Radical Formation. The chemical effect of ultrasound on aqueous solutions have been studied for many years. The primary products are H2O2 there is strong evidence for various high-energy intermediates, including HO2,... 

Sonochemistry is also proving to have important applications with polymeric materials. Substantial work has been accomplished in the sonochemical initiation of polymerisation and in the modification of polymers after synthesis (3,5). The use of sonolysis to create radicals which function as radical initiators has been well explored. Similarly the use of sonochemicaHy prepared radicals and other reactive species to modify the surface properties of polymers is being developed, particularly by G. Price. Other effects of ultrasound on long chain polymers tend to be mechanical cleavage, which produces relatively uniform size distributions of shorter chain lengths. 

The phenomenon of acoustic cavitation results in an enormous concentration of energy. If one considers the energy density in an acoustic field that produces cavitation and that in the coUapsed cavitation bubble, there is an amplification factor of over eleven orders of magnitude. The enormous local temperatures and pressures so created result in phenomena such as sonochemistry and sonoluminescence and provide a unique means for fundamental studies of chemistry and physics under extreme conditions. A diverse set of apphcations of ultrasound to enhancing chemical reactivity has been explored, with important apphcations in mixed-phase synthesis, materials chemistry, and biomedical uses. 

Mason TJ, Lorimer JP (1989) Sonochemistry Theory, applications and uses of ultrasound in chemistry, Ellis Horwood Limited, Chichester, chap 2... 

T.J. Mason, ed., "Sonochemistry the Uses of Ultrasound in Chemistry , Royal Society of Chemistry, London, (1990). 

Sonochemistry started in 1927 when Richards and Loomis [173] first described chemical reactions brought about by ultrasonic waves, but rapid development of ultrasound in chemistry really only began in the 1980s. Over the past decades there has been a remarkable expansion in the use of ultrasound as an energy source to produce bond scission and to promote or modify chemical reactivity. Although acoustic cavitation plays... 

Abstract Acoustic cavitation is the formation and collapse of bubbles in liquid irradiated by intense ultrasound. The speed of the bubble collapse sometimes reaches the sound velocity in the liquid. Accordingly, the bubble collapse becomes a quasi-adiabatic process. The temperature and pressure inside a bubble increase to thousands of Kelvin and thousands of bars, respectively. As a result, water vapor and oxygen, if present, are dissociated inside a bubble and oxidants such as OH, O, and H2O2 are produced, which is called sonochemical reactions. The pulsation of active bubbles is intrinsically nonlinear. In the present review, fundamentals of acoustic cavitation, sonochemistry, and acoustic fields in sonochemical reactors have been discussed. 

Fig. 1.2 Numerically simulated frequency spectra of the hydrophone signal due to acoustic cavitation noise. The driving ultrasound is 515 kHz in frequency and 2.6 bar in pressure amplitude, (a) For stable cavitation bubbles of 1.5 pm in ambient radius, (b) For transient cavitation bubbles of 3 pm in ambient radius. Reprinted from Ultrasonics Sonochemistry, vol. 17, K. Yasui, T. Tuziuti, J. Lee, T. Kozuka, A. Towata, and Y. lida, Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles, pp. 460-472, Copyright (2010), with permission from Elsevier...

Acoustic cavitation In this case, the pressure variations in the liquid are effected using the sound waves usually ultrasound (16 kHz to 100 MHz). The chemical changes taking place due to the cavitation induced by the passage of sound waves are commonly known as sonochemistry. 

By changing the ultrasound power, changes in the mesoporosity of ZnO nanoparticles (average pore sizes from 2.5 to 14.3 nm) have been observed. In addition to the changes in mesoporosity, changes in the morphology have also been noted [13]. Recently, Jia et al. [14] have used sonochemistry and prepared hollow ZnO microspheres with diameter 500 nm assembled by nanoparticles using carbon spheres as template. Such specific structure of hollow spheres has applications in nanoelectronics, nanophotonics and nanomedicine. 

P Christian, Dominick C (2001) The sonochemical degradation of aromatic and chloroaro-matic contaminants. In Mason TJ and Tiehm A (eds) Advances in sonochemistry ultrasound in environmental protection, Elsevier 6 102-103... 

Suslick KS, Doktyez SJ (1989) The sonochemistry of Zn powder. Am Chem Soc 111 2342-2344. Prfozorov T, Prozorov R, Suslick KS (2004) High velocity interparticle collisions driven by ultrasound. J Am Chem Soc 126 13890-13891... 

Abstract Having discussed many aspects of sonochemistry and its application in the previous chapters, a few introductory experiments in sonochemistry and sonoluminescence are presented in this chapter. These physical demonstrations are especially aimed at beginners in the field of sonochemistry making them e.g. aware of the power of ultrasound. 

Fascination with a subject increases when one sees its physical demonstration too. One of the authors recalls the very first lecture on Sonochemistry by Prof. T.J. Mason at Coventry Polytechnic, Coventry, UK and then his another lecture at Ultrasonics International, 91, at Le Tuqoute, Paris, France during 1—4 July, 1991, with few basic experiments and their results being shown to demonstrate the power of ultrasound, such as ... 

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