Potassium ultrasonically dispersed

Most of the above reactions are used for the cleavage of aryl sulphones. Recently, a note has appeared109 in which the use of potassium metal dispersed ultrasonically in toluene to cleave saturated cyclic sulphones is described. Addition of iodomethane permits the isolation of acyclic alkyl methyl sulphones (as outlined in equation (44)). 

Extrusion of S02 from unsaturated cyclic sulphones, promoted by ultrasonically dispersed potassium, is described in Reference 218. 

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). 

Colloidal potassium has recently been proved as a more active reducer than the metal that has been conventionally powdered by shaking it in hot octane (Luche et al. 1984, Chou and You 1987, Wang et al. 1994). To prepare colloidal potassium, a piece of this metal in dry toluene or xylene under an argon atmosphere is submitted to ultrasonic irradiation at ca. 10°C. A silvery blue color rapidly develops, and in a few minutes the metal disappears. A common cleaning bath (e.g., Sono-clean, 35 kHz) filled with water and crushed ice can be used. A very fine suspension of potassium is thus obtained, which settles very slowly on standing. The same method did not work in THF (Luche et al. 1984). Ultrasonic waves interact with the metal by their cavitational effects. These effects are closely related to the physical constants of the medium, such as vapor pressure, viscosity, and surface tension (Sehgal et al. 1982). All of these factors have to be taken into account when one chooses a metal to be ultrasonically dispersed in a given solvent. 

Even though sulphur dioxide extrusion from sulpholene derivatives is generally conducted either by heating in a non-polar solvent or in the presence of base, alternative reagents such as LAH, and finely dispersed potassium metal are also used. Syntheses of some tetrasubstituted butadienes were achieved by treating the corresponding sulpholenes with ultrasonically dispersed potassium metal in the presence of water (equation 73) . 

Very recently, two examples of generating enolates with metallic potassium appeared. In one case potassium was dispersed ultrasonically, in the other 18-crown-6 was added to the potassium metal (equations 8 and 9). - ... 

MMTS MsOH NBS NHMDS NMP NMR PPb Ph Pr PTC rt TBDMS Tf THF THP TLC TMEDA TMS TMSOTf Tol TOMAC Ts TsOH UDP methyl methylthiomethyl sulfoxide (=FAMSO) methanesulfonic acid N-bromosuccinimide sodium hexamethyldisililazide /V-methyl-2-pyrrolidone nuclear magnetic resonance parts per billion phenyl propyl Phase transfer catalysis room temperature t-butyldimethylsilyl triflatc (trifluoromethanesulfonate) tetrahydrofuran 2-tetrahydro-2//-pyran-2-yl thin-layer chromatography /V./V./V /V -tetramethylethylenediamine trimethylsilyl trimethylsilyl triflate p-tolyl trioctylmethylammonium chloride tosyl p-toluenesulfonic acid ultrasonically dispersed potassium... 

Deoxygenation. Ultrasonically dispersed potassium reduces azoxyarenes to azoarenes at room temperature. 

Dihydrothiophene-l,1-dioxides undergo reductive C—S bond cleavage and ring opening to furnish acyclic sulfones (after a final alkylation) <92JOC5015>. The reaction is brought about by ultrasonically dispersed potassium in the presence of a proton source, and involves two one-electron reduction steps. The final alkylation converts the sulfinate to a sulfone (Scheme 57). 

Ultrasonically dispersed potassium (UDP) has been utilized to promote the rapid, stereoselective extrusion of SO2 from di-, tri-, and tetrasubstituted 3-sulfolenes [39] (Scheme 6.56). 

Reductive dimerization of chalcones by ultrasonically dispersed potassium (UDP) is initiated by an electron transfer to the enone system. The reaction is not selective however, details are not easily available. ... 

Ultrasonically dispersed potassium (UDP) reduces a C-H bond a to activating groups. With this reagent, the Dieckmann and Thorpe-Ziegler cyclizations of hexane- and heptanedioic diesters or dinitriles proceed readily at room temperature (Eq. 21). This procedure offers many advantages in comparison to the conventional conditions (several hours in refluxing toluene). 

The use of ultrasonically dispersed potassium (UDP) in Dieckmann s condensations was previously reported. Under these conditions, 2-carboethoxy-4,4-ethylenedioxycyclo hexanone 2 and 2-carboethoxy-2-methyl-4,4-ethylenedioxycyclohexanone 3 were obtained in better yields (81-85%) under milder conditions than by literature methods (50-68%), using... 

Sulpholenes are well known precursors of 1,3-conjugated dienes. Chou and You have also shown that ultrasonically dispersed potassium (UDP) can also be used to promote extrusion of sulphur dioxide from the sul-pholene, avoiding the need to subject the substrate to high temperature thermolysis. Hence, trans-2,5-dialkyl-3-sulpholenes gave an 8 1 ratio of the (E, Z) and (E, E) dienes in high yield. However, reaction with more sensitive substrates was not attempted [110] (Scheme 46). 

However, this commonly accepted theory is incomplete and applies with much difficulty to systems involving nonvolatile substances. The most relevant example is metals. For a heterogeneous system, only the mechanical effects of sonic waves govern the sonochemical processes. Such an effect as agitation, or cleaning of a solid surface, has a mechanical nature. Thus, ultrasound transforms potassium into its dispersed form. This transformation accelerates electron transfer from the metal to the organic acceptor see Chapter 2. Of course, ultrasonic waves interact with the metal by their cavitational effects. 

The aluminum oxide layer was applied to the inner walls of the glass capillary from an aqueous dispersion in the form of aluminum hydroxide and converted In situ into aluminum oxide by heat treatment. By varying heat treatment and by blocking unwanted activities with potassium chloride, adjustment to the desired separation characteristics can be achieved [55]. To prepare the coating suspension, aluminum oxide (particles <2 urn) obtained by calcination of hydroxide is heated for 24 h at 300 °C. 20 g of the alumina is mixed with 70 ml of 5% (w/w) Baymal solution (colloidal aluminum hydroxide) and with 0.3 ml of acetic acid (>96%) and stirred for about 10 min in an ultrasonic bath. Subsequently the mixture is filtered through a wire sieve of 300 mesh and allowed to stand for 24 h for aging. The suspension thus prepared shows thixotropic behavior. 

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