Anodes, aluminum sacrificial

In the future, further studies should be addressed to improve the chemose-lectivity and diastereoselectivity of the reductive coupling process, especially searching for novel reagents and milder experimental conditions. As a matter of fact, a few novel reductive couphng procedures which showed improved efficiency and/or stereoselectivity have not been further apphed to optically active imines. For example, a new electrochemical procedure which makes use of the spatially addressable electrolysis platform with a stainless steel cathode and a sacrificial aluminum anode has been developed for imines derived from aromatic aldehydes, and the use of the N-benzhydryl substituent allowed 1,2-diamines to be obtained with good yields and dl-to-meso ratios... 

Nedelec et al. have achieved the electrochemical cross-coupling of CF3CC13 with PhCH2Br by using a sacrificial aluminum anode (Eq. 10) [24]. 

The use of reactive metal electrodes are also effective for the silylation of various organic halides and simple arenes [75]. For instance, Dunogues et al. reported that electrolysis of aryl chlorides in the presence of excess Me3SiCl in a one-compartment cell equipped with a sacrificial aluminum anode in 80 20 THF/HMPA gave the corresponding aryltrimethylsilanes (Scheme 36). When... 

P, y-Unsaturated esters (184) have been synthesized by a one-step electrochemical procedure from a-chloroesters (183) and aryl or vinyl halides (Scheme 73b) [294, 295]. This novel electroreductive cross-coupling method is based on the use of a Ni(II)(bpy) catalyst and a sacrificial aluminum anode in a one-compartment cell (Scheme 73). The whole cathodic process progresses at —1.2 V (SCE) (Scheme 73c),... 

Interestingly22, the isolated yield of CF3CHO can be increased up to 75% if the reaction is performed in the presence of a sacrificial aluminum anode and of an additive such as A1C13, or BF3. Et20. 

Bordeau and coworkers also reported that cathodic reduction of Me2SiCl2 without solvent using a sacrificial aluminum anode and a stainless steel cathode in an undivided cell produces polydimethylsilane with a very high current efficiency84. 

Cathodic reduction of (chloromethyl)dimethylchlorosilane using an aluminum anode provided polycarbosilanes besides a large amount of di- and trisilacyclic compounds (equation 67)97. On the other hand, the electrolysis in the presence of Me2SiCl2 gave bis(dimethylchlorosilyl)methane, a useful polycarbosilane precursor (equation 68)97. Similarly, polycarbosilanes were prepared from dichlorocarbosilanes using sacrificial aluminum electrodes in DME (equation 69)91. 

Reactive metal anodes are quite effective in reactions of aryl chlorides in the presence of a large excess of chlorotrimethylsilane in an undivided cell using a sacrificial aluminum anode in THF/HMPA (4 1) which provide the corresponding aryltrimethylsilanes (equations 76 and 77)101402> p is metPod does not require any diaphragms since oxidation of the aluminum anode takes place predominantly as the anodic reaction (equation 76). When excess amount of electricity is passed, traw.s-tris(lriruclhylsilyl)chlorohcxa-1,3-dienes are formed predominantly (equation 78). 

A 3-allyloxy-2-bromo ester 264 (Y=0, R2=C02Et) cyclized similarly using 20 mol% of (salen)Co complex 267 as a catalyst under reductive electrochemical conditions at a carbon fiber cathode and a sacrificial aluminum anode under constant current conditions. Tetrahydrofurancarboxylates 266 were isolated in 70% yield and a good 6 1 CK//r[Pg.266]

Electrochemical carbocyclization reactions involving the preparation of 3-, 4-, 5-, or 6-membered rings have been described. The reaction involves complexing of olefinic compounds, such as dimethyl maleate 126 and a,co-dibromide, such as 1,3-dibromopropane 127 in an undivided cell fitted with a sacrificial aluminum anode, in A-methylpyrrolidone at constant current (equation 66)99. The reaction is of special interest for the preparation... 

Cathodic protection of a hot water tanks using magnesium as the sacrificial anode is shown in Figure 1.71. Some characteristic properties of zinc, magnesium and aluminum anodes are listed in Table 1.30. 

Anode, sacrificial — a rather easily oxidizable metal, e.g., zinc, magnesium, aluminum, electrically connected with a metal construction to be protected from corrosion. Due to the formation of a -> galvanic cell the sacrificial anode is oxidized instead of the metal to be protected. Sacrificial anodes are the oldest and simplest means for electrochemical corrosion protection. 

The efficient preparation of trimethyl(trinuoroinethyl)silane via the eleetroredaction of bromo-trifluoroniethane in dimethylformamide in the presence of chlorotrimethylsilane using a sacrificial aluminum anode and nickel foam cathode (area 20 cm ) containing tetrabutylam-... 

A catalyst of the Friedel-Craft type, which promotes the acetylation of aromatic compounds, has been prepared using aluminum as sacrificial anode [177,178]. 

Sock and co workers [31] synthesized carboxylic acids by reducing alkyl bromides at platinum, gold, stainless steel, and graphite in the presence of carbon dioxide in either DMF or a THF-hexamethylphosphoramide (HMPA) mixture. Reduction of an alkyl monobromide at nickel in DMF containing TBABr and in the presence of an arylalkene and a sacrificial aluminum anode leads to an addition product [32]. 

A number of other publications deal with the electrochemical behavior of a, oj-dibromoalkanes at mercury electrodes polarographic studies [85,86] electrolyses of 1,3-dibromopropane, 1,4-dibromobutane, and 1,5-dibromopentane [87,88] reduction of 1,10-dibromo- and 1,10-diiododecane [89] and electro syntheses of phenylcyclopropane and cyclopropanol [90]. In the presence of an arylalkene, reduction of 1,3-dibromopropane or 1,4-dibromobutane at nickel in DMF containing TBABr and with a sacrificial aluminum anode yields the corresponding cyclopentane or cyclohexane adduct [32] ... 

Early workers [103] detected benzilic acid formed during the reduction of benzophenone in dimethylformamide in the presence of carbon dioxide. The carbon dioxide radical anion system is known to have E" = —2.2V (vs. SCE) [104] and will thus not be formed in preference to the ketone radical anion. Reaction occurs through trapping of aromatic carbonyl radical anions by carbon dioxide, and this has been developed into a convenient synthesis of aryllactic acids. The modern technological process uses constant current conditions. On a small scale, a divided cell with mercury cathode has been used to obtain benzilic acids from substituted benzophenones and carbon dioxide in 70-90% yields [105] and to convert 4-isopropylacetophenone to the corresponding phenyllactic acid in 85% yield [106]. On a technical scale, these reactions are best carried out in an undivided cell using a lead cathode and a sacrificial aluminum anode with dimethylformamide as solvent... 

Aluminum and aluminum-zinc alloy anodes have become the preferred sacrificial anodes for the cathodic protection of offshore platforms. This preference is because aluminum anodes demonstrate reliable long-term performance when compared with magnesium, which might be consumed before the platform has served its useful hfe. Aluminum also has better current/weight characteristics than zinc. Weight can be a major consideration for large offshore platforms. The major disadvantage of aluminum for some applications, for example, the protection of painted ship hulls, is that aluminum is too corrosion resistant in many environments. Aluminum alloys will not corrode reliably onshore or in freshwater [37]. In marine... 

Cathodic protection has been traditionally used for a long time to protect structures in seawater. Zinc bracelet anodes are installed on pipelines immersed in seawater to provide sacrificial CP to the outer surfaces of the steel pipe. Offshore structures for gas and oil exploration, drilKng, and production are commonly protected by the use of aluminum anodes on the steel structures. Cathodic protection is employed by several power plants located near coastal sites for protecting steel structures submerged in seawater. 

Jetties are individual or multiple piles interconnected together to form a structure in the seabed and support a deck. The piles of a jetty usually have half of their length in the seabed and the rest in the high tide and splash zones up to the jetty deck. They are often concrete structures reinforced with steel. Cathodic protection using sacrificial zinc or aluminum anodes is installed after the completion of the jetty. With a deepwater jetty the suspension of more than a single anode or placing of alternate anodes at different levels is necessary. A few and larger anodes are necessary while impressed current method is employed. An... 

Porcelain enamel is used mainly in high-level performance appliances. The porcelain enamel coatings are more scratch resistant and heat resistant than the thinner liquid and powder coatings however, porcelain enamel is porous. Holidays are sometimes found in the porcelain (glass). Magnesium, zinc, and aluminum anodes are used in combination with porcelain enamel coatings in water heating systems to act as a sacrificial anode. 

Silvestri G, Gambino S, Filardo G (1986) Electrochemical carboxylation of aldehydes and ketones with sacrificial aluminum anodes. Tetrahedron Lett 27 3429-3430... 

In an electrocoagulation reactor, electric current is applied to a sacrificial anode and a cathode in a processing tank. Reactions at the (aluminum or iron) anode and the cathode would be a.) On an aluminum anode ... 

Anticorrosion protection of metal structures using sacrificial magnesium, zinc, and aluminum anodes is the oldest and, at the same time, the simplest method of electrochemical protection. Galvanic anodes are mainly used in cases where the structure is covered with a good insulation coating and low currents are required for protection, and also when lack of a power supply makes realization of cathodic protection impossible. 

Figure 8-24. Sacrificial protection of a setnisubmersible rig using aluminum anodes (courtesy of Jotun Cathodic Protection A.S. Denmark).

Sacrificial Protection sa-kro-Ifi-shol pro-Itek-sh9n n (1) The use of a metallic coating, such as a zinc-rich paint, to protect steel. In the presence of an electrolyte, such as salt water, a galvanic cell is set up and the metallic coating corrodes instead of the steel. (2) Zinc or aluminum anode. 

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