Electrochemical Anodic Oxidation

Oxidation at an anode follows the same principles as oxidation by chemical electron transfer, with one exception. In the case of anodic oxidation, the radical cations are produced in a very small volume near the cathode. Even if their lifetimes are short, they are therefore liable to undergo bimolecular reactions. This effect is seen in the Kolbe synthesis. Electrolysis of a salt of a carboxylic acid, RCOOH, usually leads to good yields of the hydrocarbon R2 by the following process  

Such salts can also be oxidized chemically by electron acceptors (A) in solution, 

however, products other than the dimer R2 are usually formed. This is because the radicals R- are being produced throughout the solution, so that their concentration is low and the chance of bimolecular reactions between them correspondingly small. In the Kolbe synthesis, the radicals are produced in a very small volume next to the anode, in which their local concentration is consequently high and the chance of bimolecular reactions between them is correspondingly enhanced. 

An interesting example is the oxidation of dimethylaniline (39). Oxidation of (39) with manganic acetate in acetic acid gives as the sole isolable product 4,4 -bis(dimethylamino)diphenylethane (40). Apparently the first step in the reaction is dealkylation by the mechanism of equation (7.69), 

The formaldehyde then undergoes acid-catalyzed condensation with dimethylaniline to form the product  

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Electrochemical method [54] Silicate is determined in sea water by four different electrochemical methods based on the detection of the silicomolybdic complex formed in acidic media by the reaction between silicate and molybdenum salts. The first two methods are based on the addition of molybdate and protons in a seawater sample in an electrochemical cell. A semiautonomous method was developed based on the electrochemical anodic oxidation of molybdenum, the complexation of the oxidation product with silicate and the detection of the complex by cyclic voltammetry. Finally a complete reagent-less method with a precision of 2.6% is described based on the simultaneous formation of the molybdenum salt and protons in a divided electrochemical cell. 

Electrochemical anodic oxidation of amides and N-alkyllactams can be carried out with IV-hydroxy-phthalimide as mediator. Oxidation takes place predominantly at the endocyclic carbon a to the nitrogen. The susceptibility of five-membered rings to oxidation is much higher than that of six-membered rings. 

Polyanilines (Scheme 36) are conjugated polymers whose it electrons are delocalized over the whole molecule. They are important conducting polymers that also act as semiconductors, in a similar manner to inorganic semiconductors121 m. They are made by chemical or electrochemical (anodic) oxidation of aniline. The product, a poor textile colorant, dates from the 1860s, and is still known by the name given at that time, emeraldine. In the electrochemical process, it is possible to produce thin films directly on conductive substrates. Polyanilines have been used in photoelectrochemical devices124-126. 

The electrochemical (anodic) oxidation of tabersonine or 3-oxotaberson-ine gives dimeric products 335a and 335b, respectively (232). In the oxidation of 3-oxotabersonine the dimer 335b was the sole product, but in the oxidation of tabersonine itself some of the symmetrical 10,10 -dimer (5%) was also obtained, together with a trimer (2%) and several other, unidentified, products. 

Several oxidation techniques may be considered, such as oxygen plasma treatments, electrochemical anodic oxidation or chemical oxidation. The plasma treatment leads to a degraded interface and the anodic oxidation should require a modification of the detector achievement process. The chemical oxidation process of... 

Oxidation of primary and secondary alcohols by oxoammonium salts derived from nitroxides has become very popular because of the very mild and chemoselective reaction conditions available (Scheme 13). The stoichiometric oxidant can often be an inexpensive reagent, such as hypochlorite (bleach), O2 with a metal catalyst, electrochemical anodic oxidation, peracid, or bromine. The oxoammonium salt can be either pre-formed and used stoichiometrically or generated catalytically from the nitroxide in situ. The mechanism of the reactions is pH dependent strongly acidic conditions chemoselectively oxidize secondary alcohols with accelerated rates over primary alcohols, whereas basic or mildly acidic conditions provide chemoselective oxidation of primary alcohols in the presence of secondary alcohols. A compre-... 

Al-Ti alloy films were fabricated by magnetron sputtering of an A1 target composed with Ti insets. An area of Ti insets was from 1 to 40 % of the total sputtering area. The thickness of the films was 0.25-1.2 pm. Electrochemical anodic oxidation was carried out in 10 % aqueous solution H2SO4 at forming current densities (Jf) from... 

Although PHCs can be prepared by chemical means, the most widely used technique is electrochemical anodic oxidation. It presents several advantages, such as... 

Other oxidation processes leading to poly(disulfide)s, namely the electrochemical (anodic) oxidation of Bunte salts (bisthiosulfates) (94) as well as oligomerization and cyclization of 1,2-ethanedithiol [540-63-6] by selenium dioxide [7446-08-4] or iodine, have also been studied (95). 

In addition, as a relatively mature technique, AI2O3 nanomembranes can be obtained by electrochemical anodic oxidation, and their thicknesses, pore diameters and densities adjusted by operational conditions such as electrolytes, voltages and temperatures. Under the assistance of porous aluminum, nanowires, nanotubes and more complex nanostructures can be prepared controllably [176], and this may open the door to the preparation of functional anisotropic NF membranes for high throughput in real applications. 

Removal of an electron in solution can be accomplished in different ways, for example by use of chemical oxidants, electrochemical (anodic) oxidation, or photoinduced electron transfer (PET). However, oxidations involving chemical oxidants should be assessed carefully with respect to inner sphere oxidation mechanisms, which are known for several common metal ion oxidants. ... 

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