Applications of Ultrasound

Following are some of the important applications of ultrasound in chemical synthesis. Most of the reactions/syntheses reported are carried out at room temperature unless otherwise specified. The symbol is used for reactions carried out on exposure to ultrasound. 

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With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

As with other two-phase reactions, the application of ultrasound may lead to shorter reaction times and improved yields. ... 

DJ McClements. Advances in the application of ultrasound in food analysis and processing. Trends Food Sci Tech 6(9) 293-299, 1995. 

Lorimer P, Mason TJ (1999) Sonoelectrochemisry. The application of ultrasound in electroplating. Electrochemistry 67 924—930... 

Ohayon E, Gedanken A (2010) The application of ultrasound radiation to the synthesis of nanocrystalline metal oxide in anon-aqueous solvent. Ultrason Sonochem 17(1) 173-178... 

The interest in the synthesis and properties of delafossite structured compounds that have the general formula of ABO2 have grown due to their p-type conductivity and optical transparency. The application of ultrasound for the synthesis of ternary oxide AgMC>2 (M = Fe, Ga) has been investigated by Nagarajan and Tomar [44]. Above materials were obtained in crystalline form within 40-60 min of sonication. 

Suslick KS, Price GJ (1999) Applications of ultrasound to materials chemistry. Annu Rev Mater Sci 29 295-326... 

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... 

The purpose of this chapter will be to serve as a critical introduction to the nature and origin of the chemical effects of ultrasound. We will focus on organo-transition metal sonochemistry as a case study. There will be no attempt to be comprehensive, since recent, exhaustive reviews on both organometallic sonochemistry Q) and the synthetic applications of ultrasound (2) have been published, and a full monograph on the chemical, physical and biological effects of ultrasound is in press (3). 

The chemical and biological effects of ultrasound were first reported by Loomis more than 50 years ago (4). Within fifteen years of the Loomis papers, widespread industrial applications of ultrasound included welding, soldering, dispersion, emulsification, disinfection, refining, cleaning, extraction, flotation of minerals and the degassing of liquids (5),(6). The use of ultrasound within the chemical community, however, was sporadic. With the recent advent of inexpensive and reliable sources of ultrasound, there has been a resurgence of interest in the chemical applications of ultrasound. 

Another recent application of ultrasound to the activation of transition metals was reported (52) by Bonnemann, Bogdavovic, and coworkers. An extremely reactive Mg species was used to reduce metal salts in the presence of cyclopentadiene, 1,5-cyclooctadiene, and other ligands to form their metal complexes. The reactive Mg species, characterized as Mg(THF)3(anthracene), was produced from Mg powder in... 

The pioneering work on the chemical applications of ultrasound was conducted in the 1920 s by Richards and Loomis in their classic survey of the effects of high frequency sound waves on a variety of solutions, solids and pure liquidsQ). Ultrasonic waves are usually defined as those sound waves with a frequency of 20 kHz or higher. The human ear is most sensitive to frequencies in the 1-5 kHz range with upper and lower limits of 0.3 and 20 kHz, respectively. A brief but useful general treatment of the theory and applications of ultrasound has been given by Cracknel 1(2). 

The report by Luche and coworkers that ultrasonic waves from a common ultrasonic laboratory cleaner aid the formation of organolithium and Grignard reagents and also improve the Barbier reaction spurred much of the current interest in the synthetic applications of ultrasound(lO) ... 

Luche and coworkers extended their studies on the applications of ultrasound to synthesis to include a variety of systems. Among these applications are the syntheses of lithioorganocuprates(ll), of aldehydes from formamides(12), of organozinc intermediates(13),... 

There are a lot of further innovative cell constructions in the literature that may also be suitable for electroorganic syntheses, from laboratory up to industrial scale. Examples are rotating electrodes, application of ultrasound, and packed or fluidized particle bed three-dimensional electrodes for increasing the active electrode area and enhancing the mass transfer. A short overview is given, for example, in [1,2]. 

One of the first applications of ultrasound in medicine was the so-called ultrasonic massage introduced in Germany before the Second World War. This was introduced as a substitute for the hands of the masseur in patients who had suffered from fractures and similar injuries. Rubbing movements are capable of improving the circulation very considerably and help also to break down adhesions between muscles and their sheaths that limit the range of movement. The use of ultrasound for the treatment of sporting injuries, particularly strains and tennis elbow is now commonplace as equipment for this purpose is readily commercially available to the physiotherapist. This is one of the first uses of ultrasound in the treatment of medical problems and is part of a new field of medicine called therapeutic ultrasound [15]. 

The potential of sonochemistry was identified over sixty years ago in a wide ranging paper entitled The Physical and Biological Effects of High Frequency Sound-Waves of Great Intensity [13]. Over the few years which followed this paper a great deal of pioneering work in sonochemistry was carried out and, as a result of this, two reviews on the applications of ultrasound in polymer and chemical processes were published... 

Today one of the most common chemical applications of ultrasound is the initiation of a reluctant Grignard reaction. The quantitative effects of ultrasound on the induction times for the formation of a Grignard reagent in various grades of ether is given in Tab. 3.2 [88]. 

On the other hand stable cavitation (bubbles that oscillate in a regular fashion for many acoustic cycles) induce microstreaming in the surrounding liquid which can also induce stress in any microbiological species present [5]. This type of cavitation may well be important in a range of applications of ultrasound to biotechnology [6]. An important consequence of the fluid micro-convection induced by bubble collapse is a sharp increase in the mass transfer at liquid-solid interfaces. In microbiology there are two zones where this ultrasonic enhancement of mass transfer will be important. The first is at the membrane and/or cellular wall and the second is in the cytosol i. e. the liquid present inside the cell. 

Combined Application of Ultrasound with Ultraviolet Light... 

There are a few reports on the combined application of ultrasound and ultraviolet light (UV) for the destruction of chemical pollutants. A study of the oxidation of humic acid and trihalomethane precursors with ozone revealed that the most effective destruction of the organic carbon compounds was achieved when both uv and ultrasound were used in combination with ozonation [35]. In other cases e. g. the removal of 1,1,1-tri-chloroethane from aqueous solutions, the combined application of ultrasound and UV proved to be more efficient than the use of either technique individually [36]. 

T.J. Mason, J.P. Lorimer, S. Saleem, and L. Paniwnyk, Controlling emissions from electroplating by the application of ultrasound. Research project sponsored by the UK Health and Safety Executive, 1996. 

We have already seen in this section how ultrasound, like milling, is capable of producing chain scission and thus give rise to macroradicals. It is therefore not surprising that the application of ultrasound to the synthesis and modification of polymers has attracted, and continues to attract, the attention of many investigators. 

SO then the application of ultrasound to the NVP system ought to lead to a destruction of the complex and a decrease in the propagation rate (R ). Except for the pure monomer system, where there could not be H-bonding since water was absent, all values... 

There are at present only a few commercial applications of ultrasound in the plastics industry. The best knovm is probably the welding of thermoplastics, a process which now lends itself readily to automation. In common with the welding of metals, the ultrasonic welding of plastics is primarily a hot stage. In the process ultrasound is applied to two layers of plastic, heat is generated at the interface causing the material... 

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