Sacrificial anodes synthesis

A typical example is the synthesis of oxalic acid. Electrochemical synthesis of oxalic acid by reduction of C02 in aprotic media with a Zn sacrificial anode was brought to pilot scale by the Dechema Institute some years ago (1981) [177]... 

Aryl- or heteroarylzinc species have been successfully synthesized from the corresponding aryl or heteroaryl bromides or chlorides in high yields, on the laboratory scale (10 mmoles of substrate). The use of cobalt as catalyst allowed the synthesis of organozinc reagents using the sacrificial anode process with a wide variety of solvents. 

Metals can be used as sacrificial anodes in the electrochemical synthesis of anhydrous salt and complexes. This method frequently produces chromium(IH) complexes, but electrochemi cal oxidation of chromium in a mixture of concentrated aqueous HBF4 and acetonitrile yield [CKMeCN KBF,),.82... 

Direct electrochemical synthesis is carried out according to the next procedure. Sheets of copper, nickel, or zinc are used as sacrificial anodes, and platinum is used as the cathode. Methanol is used as a solvent and LiC104 as a supporting electrolyte. The ligand (0.5 g) is dissolved in methanol (30 mL) by heating and then the obtained solution is cooled to room temperature. The electrolysis is carried out for 1 hr (current 20 mA applied voltage 20-30 V). The formed solid is filtered, washed with hot methanol (3x5 mL), and dried in air. 

The reductive-trimethylsilylation, via either a chemical (Li/HMPA/THF) or an electrochemical (undivided cell/sacrificial anode) process, led to the synthesis of 1-(trimethylsilyl)alkylamines (RSMAs).191 Thus, l-(trimethylsilyl)f-amylamine was prepared in 67% yield from pivalaldehyde iV-(trimethylsilyl)imine, after hydrolysis of the intermediate silazane. 

If a divided cell is used, this reaction can also be carried out using BDD electrodes, avoiding sacrificial anodes and therefore simplifying workup procedure (Fig. 5.14) (Reufer et al. 2006). The MHA yield of this process is not very high but this is a remarkable example for the versatility of BDD electrodes in preparative electroorganic synthesis. 

The formation of silicon-silicon bonds constitutes the key step in these syntheses. To avoid the use of sodium, a simple, inexpensive, and practical electrochemical technique using an undivided cell, a sacrificial anode, and a constant current density has been developed allowing a facile synthesis of di-, tri-, or polysilanes including polydimethylsilane. 

Copolymerization of two different dichlorosilanes can also be achieved by the reduction using a sacrificial anode [177,178]. It is interesting that copolymerization of sila-functional dichlorosilanes with simple dichlorosilanes took place smoothly to provide an elegant route to functionalized polysilanes [178]. As to the synthesis of sila-functional polysilanes, the electrochemical reduction of perfluoroalkyl-substituted trichlorosilane to give perfluoroalkyl-substituted polysilane is interesting [179]. 

A magnesium sacrificial anode is also effective for the synthesis of Si-Ge and Ge-Ge bonds. This method is quite successful for the preparation of polygermanes and germane-silane copolymers [Eq. (49)] [183]. Polygermanes were also prepared by conventional electrochemical reduction of dihalogermanes using a Pt cathode and an Ag anode [184]. 

We succeeded in the synthesis of different hydrodisilanes by electroreductive coupling of chlorohydrosilanes employing the cell design of T. Shono. All electrolyses were performed in an undivided cell equipped with a magnesium sacrificial anode and a cylindrical stainless steel cathode. The reactions were carried out under constant current conditions (1 mA cm ) in THE using MgCh as supporting electrolyte. 

The synthesis of cyclic carbonates in RTILs, via cycloaddition of cathodically activated carbon dioxide to epoxide, has been reported by Deng et al. [139]. Ionic liquids, saturated with CO by bubbling at normal pressure and containing the epoxidic substrate, were electrolyzed in an undivided cell (Cu as cathode. Mg or Al as sacrificial anode). The electrolyses were carried out under potentiostatic conditions at a potential negative enough to the selective reduction of CO to CO (E=-2.4 V vs. 

There are two basic approaches to the synthesis of nanosized materials top-down or bottom-up methodologies (Table 6.2). Top-down refers to pulverization of bulk material into fine particles that can be collected as solid powder, suspended in a liquid, or deposited directly on the electrode surface. The particles are usually obtained by physical methods, such as thermal evaporation, sputtering, or laser ablation. In addition, metallic nanosized particles can also be obtained via electrochemical synthesis, exploiting the dissolution of a sacrificial anode [59]. 

Metal nanostructures Chemical and electrochemical reduction of metal salts in solution and at liquidlliquid interface [67- 74, 84] Electrochemical synthesis from sacrificial anode [59, 95, 96]... 

Chaussard J, Folest JC, Nedelec JY, P ichon J, Sibille S, Troupel M (1990) Use of sacrificial anodes in electrochemical functionalization of raganic halides. Synthesis 369-381. doi 10.1055/s-1990-26880... 

An alternative synthetic route to silylated thiophene and oligomers has recently been proposed from chloro- and bromothiophene derivatives. This involves an electrochemical technique using a metallic sacrificial anode and provides a selective synthesis of silyl derivatives [15,16]. The bromothiophenes are more easily reduced... 

A titanium(O) colloid, prepared by the reduction of TiCU with KBEtsH, has been used in the synthesis of indoles [260]. Nanostructured titanium clusters, produced electrochemically by using a titanium sacrificial anode as the metal source and Bu4NBr in THF as the electrolyte and stabilizer, were found to induce olefin-forming McMurry-type coupling of oxoamides, aromatic aldehydes, and ketones [261]. 

Electrochemical synthesis of tetra and pentasilanes. Larger polysilane oligomers could also be obtained using the aluminum sacrificial anode technique. Thus, the electrolysis of 1-chloro-l-phenyltetramethyldisilane, electrochemically prepared as described above, led to the corresponding tetrasilane in 85 % yield (Equation 14). 

The sacrificial anode electrochemical synthesis under controlled current seems to be a simple alternative to the use of akali metals, especially for the synthesis of di-, tri-, polysilane oligomers and polymers in high current efficiency and yield. This method is easy and inexpensive the reaction only needs a bar of a common metal such as Al, Mg, Cu it runs at room temperature a stabilized regulated supply is convenient not only because the reaction can be stopped instantly, but because, when needed, the dependency of the selectivity upon the quantity of electricity and upon the nature of the electrodes makes the reaction easy to control. Moreover, extrapolation to an industrial scale can be anticipated. 

Then, the use of nickel(II) or cobalt(II) complexes as catalyst associated to the sacrificial anode process allows synthesis of functionalized mono- or diorganozinc species in a simple and efficient manner. Alternating Jt-conjugated copolymers, based on this electrochemical preparation of intermediate aryldizinc species and their subsequent palladium-catalyzed coupling with unsaturated dihalogenated compounds, can be synthesized. Furthermore, aromatic ketones are synthesized efficiently via cobalt-catalyzed cross-coupling reaction between arylzinc bromides and acid chlorides. 

Low-valent cobalt pyridine complexes, electrogenerated from CoCl2 in DMF containing pyridine and associated with a sacrificial zinc anode, are also able to activate aryl halides to form arylzinc halides.223 This electrocatalytic system has also been applied to the addition of aryl bromides containing an electron-withdrawing group onto activated alkenes224 and to the synthesis of 4-phenylquinoline derivatives from phenyl halides and 4-chloroquinoline.225 Since the use of iron as anode appeared necessary, the role of iron ions in the catalytic system remains to be elucidated. 

Synthesis with sacrificial electrodes is employed as a direct method in several other preparations of organometallic compounds and complexes. 3-Hydroxy-2-methyl-4-pyrone derivatives of Sn 1 (and of Zn, Cu, In and Cd as well) were prepared using the metal as an anode. The low oxidation state Sn(II) compound is obtained by direct electrolysis134. 

The reactions appear to be similar to organometallic synthesis, where the reduction is performed by the metal instead of electricity. However, these reactions have been shown to be essentially different from the corresponding organometallic reactions. This method has valuable advantages. As the anode reaction is controlled, an undivided cell can be used, the reaction occurs in one-step, the conditions are quite simple, and so on. Sibille and Perichon et al. have found that the sacrificial zinc anode is quite effective for trifluoromethylation of aldehydes to form trifluoromethylated alcohols in almost quantitative yields (Eq. 6) [19]. The reaction proceeds via the reduction of Zinc(II) salts, followed by a chemical reaction between the reduced metal, CF3Br, and aldehyde. 

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