Ultrasonic cleaning bath

This is probably the most accessible and cheapest piece of ultrasonic equipment available and it is for this reason that so many sonochemists begin their studies using cleaning baths. 

The construction of a bath is very simple - it generally consists of a stainless steel tank with transducers clamped to its base (Fig. 7.8). One of the basic parameters in ultrasonic engineering is power density which is defined as the electrical power into 

Once the bath has been chosen the correct design for the reaction vessel must be used. 

Another important consideration when using baths to perform sonochemical reactions is that it may be necessary to stir the mixture mechanically to achieve the maximum effect from the ultrasonic irradiation. This is particularly important when using solid-liquid mixtures where the solid is neither dispersed nor agitated throughout the reaction by sonication alone and simply sits on the base of the vessel where it is only partially available for reaction. The reason that additional stirring is so important in such cases is that it ensures the reactant powder is exposed as fully as possible to the reaction medium during sonication. 

Despite the advantages gained from the use of such a simple piece of apparatus there are a number of reservations which should be borne in mind when using this method of energy input. 

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Owing to the widespread use of ultrasonic cleaning baths, it is not surprising that many early sonochemical experiments were directed at reactions where dirty metal surfaces were thought to be the cause of inefficiencies. Reactions typified by Grignard and Simmons Smith reactions (Scheme 7.11) are often not predictable, sometimes having long induction periods followed by violent exotherms. Frequently, small... 

Figure 5.5 shows the changes in the concentration of Au(III) at different ultrasound intensities [29], where the intensities are determined by the calorimetric method. It can be seen that the concentration of Au(HI) decreases with increasing irradiation time and the reduction behavior is clearly dependent on the ultrasound intensities. At more than 1.20 W cm-2, the reduction of Au(III) was completely finished within the 20 min irradiation. On the other hand, it was also observed that no reduction occurred in a conventional ultrasonic cleaning bath (Honda Electric Co., W-113, 28 kHz, 100 W, bath-volume ca. 2 L) [29]. 

In the preceding chapters many aspects of sonochemistry and its application have already been discussed in details and now to conclude, few experiments are being discussed here to make the beginners in the field of sonochemistry, especially the undergraduate students, to ride on the sound wave and begin their journey of sonochemistry with some of these experiments, which can be conveniently carried out with an ultrasonic cleaning bath (Fig. 15.1) or an ultrasonic probe (Fig. 15.2) of 20 kHz, available commercially abundantly. 

Reason Initial fast reaction of Zn metal with acid decreases due to a thin oxide coating on the surface of the metal, hindering the further intimate contact of metal with acid. However, when the solution flask was immersed in the ultrasonic cleaning bath, the surface of the metal is cleaned by the agitation generated due to mechanical vibration and acoustic cavitation, exposing the fresh metal surface for reaction with the acid. As a secondary effect of ultrasound, the H2 gas bubbles... 

Procedure 10% aqueous solution of potassium iodide, KI, when exposed to sunlight, liberated I2 due to the photolytic decomposition and gave blue colour with freshly prepared starch solution. The intensity of blue coloured complex with the starch increased many fold when the same solution was kept in the ultrasonic cleaning bath. As an extension of the experiment, the photochemical decomposition of KI could be seen to be increasing in the presence of a photocatalyst, Ti02, showing an additive effect of sonication and photocatalysis (sono-photocatalysis) However, the addition of different rare earth ions affect the process differently due to the different number of electrons in their valence shells. 

The ultrasonic cleaning bath is clearly the most accessible source of laboratory ultrasound and has been used successfully for a variety of liquid-solid heterogeneous sonochemical studies. There are, however, several potential drawbacks to its use. There is no means of control of the acoustic intensity, which will vary from bath to bath and over the lifetime of a single cleaning bath. In addition, their acoustic frequencies are not well controlled and differ from one manufacturer to another, and reproducibility from one bath to another may therefore suffer. Reproducible positioning of the reaction flask in the bath is critical, since standing waves... 

The sonochemistry of the other alkali metals is less explored. The use of ultrasound to produce colloidal Na has early origins and was found to greatly facilitate the production of the radical anion salt of 5,6-benzo-quinoline (225) and to give higher yields with greater control in the synthesis of phenylsodium (226). In addition, the use of an ultrasonic cleaning bath to promote the formation of other aromatic radical anions from chunk Na in undried solvents has been reported (227). Luche has recently studied the ultrasonic dispersion of potassium in toluene or xylene and its use for the cyclization of a, o-difunctionalized alkanes and for other reactions (228). 

Another recent application to the activation of transition metals was reported (247) by Bonnemann, Bogdavovic, and co-workers, in which an extremely reactive Mg species was used to reduce metal salts in the presence of cyclopentadiene, 1,5-cyclo-octadiene, and other ligands to form their metal complexes. The reactive Mg species, characterized as Mg(THF)3 (anthracene), was produced from Mg powder in THF solutions containing a catalytic amount of anthracene by use of an ultrasonic cleaning bath. A plausible scheme for this reaction has been suggested ... 

The ultrasonic cleaning bath is the most common source of ultrasound in the laboratory and was the equipment used in most of our investigations. The acoustic intensity is far less than the immersion horn but the low price, less than 200 for a 4" x 9 bath that holds flasks up to 1 liter in size, compared to nearly 2000 for a modest horn setup probably accounts for the difference in popularity. 

The ruthenium complex is moderately soluble in methanol. Suspension in an ultrasonic cleaning bath is employed to achieve complete solution. 

Ultrasonic cleaning is another major application for power ultrasound. It is now such a well-established technique that laboratories without access to an ultrasonic cleaning bath are in a minority. It is important to recognise the historical significance of the development of ultrasonic cleaning technology on the growth of sonochemistry because, in the early years, the humble laboratory cleaner was almost certainly the first ultrasonic apparatus used by chemists. 

Ogashasa and Mataka [62] have employed crossed Kolbe electrolyses of deuterated phenylacetates and succinates to produced derivatives of 4-phenylbutyric acids. In control experiments to produce deuterated bibenzyls from phenylacetate without the presence of succinate, they obtained 11 % of dimer with pyridine present, under normal conditions, and 41 % of dimer with an ultrasonic cleaning bath. This increase in yield was ascribed to a sweeping clean of the electrode by ultrasound. 

Laboratory Equipment Based on the Ultrasonic Cleaning Bath... 

In cases where low intensity irradiation is needed batch treatment could be as simple as using a large-scale ultrasonic cleaning bath as the reaction vessel. However the tank would need to be constructed of a material which was inert towards the chemicals involved. An appropriate grade of stainless steel might prove adequate or plastic tanks could be used. In the latter case however the transducer would need to be bonded onto a stainless or titanium plate and this assembly then bolted to the tank. A useful variant to this and indeed one which offers greater flexibility in use is the sealed, submersible transducer assembly (Fig. 7.17). With either system some form of additional (mechanical) stirring would almost certainly be needed. 

If particles are aggregated after the opsonization procedure, vortex the particles vigorously. If vortexing does not disaggregate the particles, then place the tube containing the particles in an ultrasonic cleaning bath for 10 min. 

To a suspension of UDP (4.5 mmol) in toluene (10 ml) in a laboratory ultrasonic cleaning bath under N2 was added a solution of 2,2,5,5-tetraethyl-3-sulfolene (1.5mmol) in toluene (10ml). The sonication was continued for 30 min, during which time a bright-blue colour developed. A solution of t-BuOH in THF (0.45 mol dm"3,4.4 mmol) was added dropwise over a period of 30 min, whereupon the potassium was completely consumed. The mixture was filtered through a short silica gel column to remove the solid precipitate, and the filtrate was concentrated under reduced pressure. Purification by HPLC (Lichrosorb column, hexane) yielded the corresponding diene in a 92% yield. 

Frozen stopcock joints, or adapters or still-heads in empty flasks, may frequently be freed by immersion in an ultrasonic cleaning bath (Section 2.1, P-29). 

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