Sonochemistry metal activation

Metal activation, and sonochemistry, 1, 314 Metal alkoxides, synthesis, 12, 51 Metal-to-alkyne ligand charge-transfer transitions, rigid-rod transition metal—acetylide polymers,... 

In many syntheses activation is not effected by sonochemical preparation of the metal alone but rather by sonication of a mixture of the metal and an organic reagent(s). The first example was published many years ago by Renaud, who reported the beneficial role of sonication in the preparation of organo-lithium, magnesium, and mercury compounds [86]. For many years, these important findings were not followed up but nowadays this approach is very common in sonochemistry. In another early example an ultrasonic probe (25 kHz) was used to accelerate the preparation of radical anions [87]. Unusually for this synthesis of benzoquinoline sodium species (5) the metal was used in the form of a cube attached to the horn and preparation times in diethyl ether were reduced from 48 h (reflux using sodium wire) to 45 min using ultrasound. 

Organoaluminum sonochemistry is not yet well developed despite the synthetic and economic interest. Aluminum, a ductile metal, is easily activated by sonication, as evidenced by the use of foils to determine the energy of cleaning baths. Alkyl halides react with aluminum at room temperature in THF to give the sesquihalide, reduced to the trialkyl compound in the presence of magnesium. Examples are known with bromomethane or -ethane.1 2,183 reaction occurs with stirring under similar conditions. Triethylaluminum was used in sonochemical transmetallation reactions leading to zinc and boron alkyls (Eq. 38). 

Abbasi, A. R., Akhbari, K., and Morsali, A. Dense coating of surface mounted CuBTC metal-organic framewoik nanostructures on silk fibers, prepared by layer-by-layer method under ultrasound irradiation with antibacterial activity. Ultrasonics Sonochemistry, 19, 846-852 (2012). 

In these direct reactions of metals such as lithium, magnesium, sodium, potassium and zinc, using sonochemistry, in which the surface of the metal is activated by irradiation by ultrasonic waves, has recently been performed [22,23]. For example, n-PBr [24], -BuBr [25] or PhBr [25] reacts with lithium metal in an ether type solvent (ethyl ether or THF) at —10 or — 60 C for 90 or 180 min in the absence of ultrasonic waves and the yields of /i-PrLi, /i-BuLi and PhLi are 78, 56 and 92 %, respectively. However, in the reactions under ultrasonic waves used for 10-30min, the yields are 90%, 61 % and 95%, respectively as shown in eq. (3.3) [23]. 

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