Cleaning baths

No dimensional change Proprietary brands of alkaline cleaners may be used provided these do not attack metal Soda ash with washing soda and soap are suitable for preparing alkaline cleaning baths No dimensional change unless much impurity is present For small delicate parts 0 1-0-5% silver chromate may be added to reduce attack caused by impurities such as chloride in corrosion product... 

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. 

See CLEANING BATHS FOR GLASSWARE See other glass incidents... 

It is well to have a hot sulfuric-nitric acid cleaning bath in the same hood, so that apparatus need not be handled in the open laboratory. The large separatory funnel is conveniently... 

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 cup-horn configuration, shown in Fig. 8, was originally designed for cell disruption but has been adopted for sonochemical studies as well (81). It has greater acoustic intensities, better frequency control, and potentially better thermostating than the cleaning bath. Again, however, it is very sensitive to the liquid levels and to shape of the reaction vessel. In addition, the reaction vessel faces a size restriction of 5 cm diameter. 

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). 

Finally, an improved synthesis of (rj6-l, 3,5-cyclooctatriene)-(i74-l,5-cyclooctadiene)ruthenium(0) has been reported which utilizes a cleaning bath to hasten the Zn reduction of RuCl3 in the presence of 1,5-cyclooctadiene (240). The use of ultrasound in simple reductions using Zn are a likely area for further development. 

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 reduction of transition metal halides with Li has been recently extended by Boudjouk and coworkers for Ullman coupling (benzyl halide to bibenzyl) by Cu or Ni, using a low intensity cleaning bath (5J.). Ultrasound dramatically decreased the time required for complete reduction of the metal halides ( 12 h without, <40 minutes with ultrasound). The subsequent reactivity of the Cu or Ni powders was also substantially enhanced by ultrasonic irradiation. This allowed significant increases in the yield of bibenzyl (especially for Ni) at lower temperatures, compared to simple stirring. 

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. 

MW monomode reactor Ultrasound (cleaning bath) Conventional heating (oil bath)... 

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