Electrolysis sacrificial anode

Low-valent lanthanides represented by Sm(II) compounds induce one-electron reduction. Recycling of the Sm(II) species is first performed by electrochemical reduction of the Sm(III) species [32], In one-component cell electrolysis, the use of sacrificial anodes of Mg or A1 allows the samarium-catalyzed pinacol coupling. Samarium alkoxides are involved in the transmet-allation reaction of Sm(III)/Mg(II), liberating the Sm(III) species followed by further electrochemical reduction to re-enter the catalytic cycle. The Mg(II) ion is formed in situ by anodic oxidation. SmCl3 can be used in DMF or NMP as a catalyst precursor without the preparation of air- and water-sensitive Sm(II) derivatives such as Sml2 or Cp2Sm. 

Tin adducts of the type Sn(C>2R) were obtained in the electrolysis of aromatic diols with tin as the sacrificial anode R(OH)2 = 1, 2-dihydroxybenzene (catechol), tetrabromo-cathechol, 2,3-dihydroxynaphthalene and 2,2/-dihydroxybiphenyl yields, based on mass loss of the anode, range within 75-94 %136. 

Moreover, in the divided cell the exo.endo ratio of bromosilanes was 91 9 in the anode compartment bnt only 52 48 in the cathode compartment. Thus, the nature of the ultrasonic effect was explained assuming that beside the electrochemical silylation at the cathode, a parallel silylation process occurs at a magnesium anode, namely the silylation by 70 of an intermediate Grignard reagent produced from dibromide 69. It appears as a rare example of the anodic reduction However, the increase in the current density dnring electrolysis cansed a decrease in the apparent current efficiency. This observation indicates a chemical natnre of the anodic process. Of course, the ultrasonic irradiation facihtates the formation of the organomagnesium intermediate at the sacrificial anode and the anthors reported a similar ultrasonic effect for the nonelectrochemical but purely sonochemical... 

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. 

Zn, Cd, Co, Ni, and Cu sheets (2x2 cm2) were used as sacrificial anodes and platinum wire was used as inert cathode. Methanol (50 mL) was used as solvent and Me4NC104 (10 mg) as a supporting electrolyte. The electrolysis was carried out at 7 = 30mA and initial K = 20V for 1.5 hr at 25°C in an argon stream. 2-Tosylaminoaniline, pyridine-2-carbaldehyde, or 2-(N-2-tosylaminophenyl)aldiminopyridine (1 mmol) were used as ligands. 

An additional experiment was carried out with Me2SiCl2, using Zn as sacrificial anode, as this metal is easily available and thus appropriate for large scale electrolyses. Unfortunately, it is too noble for this kind of electrolysis. The only detected cathodic reaction is the reduction of the anodically formed Zn ions, thus covering the cathode surface with a Zn-coating. 

Electrolytic procedures employing gallium metal in the form of a sacrificial anode can also be conveniently used to synthesize salts of the gallium(Ill) complex halide ions, [GaX4]. A straightforward procedure described here involves electrolysis of gallium in aqueous acid, HX, followed by heating to oxidize any Ga(II) species to Ga(III) ... 

Reductive coupling. Using Mg as a sacrificial anode to perform electrolysis esters are reductively coupled to either a-diketones or 1,2-bistrimethylsilylalkenes, depending on the nature of the additives. 

The outstanding electron acceptor property of carbon dioxide can be used for the reductive coupling to oxalic acid ((13), Scheme 7). Electrolysis is conducted in DMF in an undivided cell using zinc as a sacrificial anode. Unfortunately, only a few details are reported about this particular process [33]. A current density of 6 mA/cm with 12 mM NBU4BF4 as a supporting electrolyte was employed and provided a current efficiency of 60%. 

In the former, a deliberate electrolysis cell is set up between the structure to be protected and a number of strategically positioned anodes of another mital. The essential property of a sacrificial anode is its ability to dissolve freely at a reasonably uniform rate at a potential negative to the corrosion potential of the metal to be protected in order to provide a consistent and sufficiently high protective current to the steel. Figure 10,27(a) illustrates the principle of cathodic protection using sacrificial anodes. The dissolution of the auxiliary metal will cause the equilibrium potential of the metal to be protected to shift to a more negative value. While both metals have almost the same potential (there will be an iR drop between sites) the auxiliary metal will function as an anode while the surface to be protected will become cathodic. It is apparent that the overall rate of metal loss will increase but it is the auxiliary metal that dissolves the rate of metal loss from the protected surface decreases hence, the term sacrificial anode. 

This technique is performed using a sacrificial anode experimental set-up, and is referred to as sacrificial anode electrolysis. During the process, the stabihzing effect can occur either at the anode or at the cathode. In the former case, the anode is made from the metal to be electrodispersed as nanostructures when the applied potential is sufficiently high, the anode dissolves into metal ions that subsequently are precipitated due to the presence of hydroxides or other anions [316]. 

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