Cathodic generation

For Fe it follows from Eq. (2-530 that = -0.64 V. This value is 0.21 V more negative than the protection potential i/cu-cuso4 = -0.85 V which is adopted in practice (see Fig. 1-12) [22,23]. This more positive potential results because 5is actually greater and the cathodically generated surface films give additional protection [24-26]. 

O. R. Brown u. J. A. Harrison. Reaction of cathodically generated Radicals and Anions, J. Electroanal. Chem. 21, 387 (1969). 

Rosamilia JM, Miller B (1986) Cathodic generation of CdSexTei x at Te film electrodes. J Electroanal Chem 215 249-260... 

Cells for the hypochlorite production do not principally require a separator, since cathodically generated hydroxide... 

There is huge potential in the combination of biocatalysis and electrochemistry through reaction engineering as the linker. An example is a continuous electrochemical enzyme membrane reactor that showed a total turnover number of 260 000 for the enantioselective peroxidase catalyzed oxidation of a thioether into its sulfone by in situ cathodic generated hydrogen peroxide - much higher than achieved by conventional methods [52],... 

The addition of cathodically generated butyl radicals to aromatic rings forms cyclic alcohols with high stereoselectivity (Scheme 36) [78]. 

Cathodic generation of Sx species in the presence of alkylhalogenides provides polysulfides Alk-5jc-Alk (x =... 

Scheme 9 Intramolecular reaction of a cathodically generated nucleophile with an electrophile.

Cathodic substitution stands for C,C bond or C, heteroatom bond formation with cathodically generated anions. The question of regioselectivity is encountered in the reaction of such anions with allyl halides (path a) or in the reaction of allyl anions generated in an ECE process from allyl halides (path b). Cathodic reductive silylation of an allyl halide proceeds regioselectively at the less substituted position (Fig. 15) [91]. From the reduction potentials of the halides it is proposed that the reaction follows path b. 

The Reformatsky reaction can also be performed electrochemically either directly or using a mediator. Ni-catalysis has proven to be an efficient way to prepare j3-hydroxy ester or nitrile from the corresponding a-chlorocompounds (Table 14) [94]. Here again the first step is the oxidative addition of the cathodically generated Ni°bpy to the halocompound. The nature of the sacrificial anode also plays a crucial role in this reaction, though the formation of an organozinc intermediate has not been fully demonstrated. 

Also the concentration differenee between the anode and cathode generates a Nernst potential, AE = RT/F ln(Cj,/c,.), therefore... 

A principally different approach for the indirect electrochemical oxidation of aromatic compounds goes via the formation of hydroxyl radicals from cathodically generated hydrogen peroxide and from reductively formed iron(II) ions. The thus in situ formed Fenton reagent can lead to side-chain as well as nuclear oxidations of aromatic compounds. Side-chain oxidations to form benzaldehydes according to Eqs. (18)—(24) can also be initiated by the redox pairs and Cu instead of... 

The addition of copper(II) ions favors the formation of the acetoxy hexenoic acids (current yield 78%) while cathodically generated copper(I) catalyzes the transformation of the acetoxy hexenoic acids to the lactone. 

The indirect electrochemical generation of propylene oxide via propylene chloro- or bromohydrin using anodically generated hypochlorite or hypobromite has been studied very intensively. The reason is the lack of a technically useful process for the synthesis of propylene oxide by way of heterogeneous catalysis. The propylene halohydrins are saponified using the cathodically generated sodium hydroxide (Eqs. (42)-(47)) (Table 4. No. 12-15)... 

For about twenty years there has been a growing realisation that the deliberate cathodic generation of anionic bases, in aprotic solvents, might be preparatively convenient and offer possibilities for control of such factors as base strength and base concentration. The term probase (PB) has come into regular use to describe a compound which on reduction is converted into an intermediate which acts predominantly as a base such bases are described as electrogenerated bases (EGB s). 

The formation of carbanions, according to Scheme 6, has been much studied but has proved to be of little preparative use. The benzyl anion, generated from benzyl-dimethylsulphonium tosylate, reacted with acrylonitrile but the addition product was formed in only low yield Similarly the reactive ylid formed by deprotonation of trimethylsulphonium salts has been cathodically generated and trapped by several aldehydes and ketones as well as ethyl maleate and fumarate examples are given in Scheme 7. For the best case (benzophenone), the epoxide was formed in 40%... 

The cathodic generation of superoxide is experimentally simple. The reactions are carried out in a conventional divided cell (H-cell), at a mercury cathode, and. 

Fig. 5.35 Apparatus for controlled-current coulometry. The case for neutralization titration of an acid by internal cathodic generation of OhT. GE generating electrode CE counter electrode.

Hypochlorite and chlorate production rely on reacting the anodically evolved chlorine in dissolved form with cathodically generated hydroxyl ions due to homogeneous reaction kinetics. In chlorate production the formation of hypochlorite is followed by disproportionation of the hypochlorite to chloride and chlorate. 

In cathodic addition reactions solvated electrons, radical anions or anions are generated at the cathode and added to activated or unactivated double or triple bonds. This broad spectrum of reactions is partially treated a) in section 8.2 when group conversion generates a reactive intermediate which undergoes addition reactions 1 S5a,b and b) in section 12.2 when olefins are coupled via addition of a cathodically generated radical anion to an activated double bond. 

An intramolecular nucleophilic substitution of the dimethyl sulfide group by a cathodically generated radical anion is postulated in the formation of the in-dane derivative 133 from the sulfonium salt 134 (Eq. (203)). 

Addition of cathodically generated radicals to double bonds (Eq. (209)) ... 

Here the cathodically generated hydroxymethyl radical adds to the double bond to form a new radical, which is subsequently reduced and protonated to give product. 

Addition of cathodically generated radical anions to activated double bonds ... 

Cathodic reduction of ammonium salts RR 3N+ in aprotic media, e.g., DMF, yields dimers R-R, for e.g., R=benzyl, fluorenyl, in moderate yields (15-30%) s03l Free radicals are assumed as intermediates, as inactive dimers were obtained from optically active ammonium salts RR 3N+. This rules out a conceivable S t2 reaction between cathodically generated R and RR 3N+ as products with partially inverted configuration should be obtained this way. Reduction of quaternary ammonium salts R4N+ in hexamethylphosphortriamide yields hydrocarbons RH and olefins RH(-H2) as main products and dimers R-R as minor side products, whose formation is rationalized by assuming radicals R as intermediates... 

Some representative examples of cathodically generated radical anions are compiled below (Table 18). 

The use of these cathodically generated anions Rm for nucleophilic displacement of halogen in Rm X offers an elegant synthesis for unsymmetric bimetallic species, e.g.,... 

Nowadays, the most commonly used DO electrode is the polarographic that employs an electrochemical method, through the reduction of molecular oxygen at the platinum electrode (cathode) generating electrons for the silver oxidation at the silver/silver chloride electrode (anode). In this type of sensor, it is necessary to impose an external voltage and the resulting current is measured and converted into dissolved oxygen concen-... 

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