Electrogeneration of base

Reduction of alkyltriphenylphosphonium salts in aprotic media leads to the formation of ylids [202,203]. The formation of ylids as a result of the electrogeneration of bases (EGB) [204] is discussed in Chapter 30. 

The most traditional approach for the electrodeposition of metal oxides and hydroxides is based on the cathodic electrogeneration of base [6]. Depending upon the deposition potential, choice of the anion and the pH of the solution, various reactions take place at the cathode, such as the reduction of nitrate ions in aqueous solutions. These reduction reactions cause a local pH increase in vicinity of the cathode either by the consumption of protons or by the generation of hydroxide ions as in the case of nitrate reduction, which subsequently leads to the precipitation of metal hydroxides. The best known application of this technique is the synthesis of nickel hydroxide by the electroreduction of aqueous nickel nitrate solutions. Depending on the metal and deposition conditions, this cathodic technique often yields hydroxides rather than oxides, making a post-deposition calcination for the transformation of the hydroxide to the oxide necessary. Unfortunately, the deposited amorphous hydroxides are often metastable. Other cathodic electrodeposition methods involve the direct reduction of the oxidation state of the metal cation and deposition of the oxide onto the electrode [9]. 

Electrolytic deposition occurs when cathodic reactions produce colloidal particles in solution next to the electrode surface. This method has an electrogeneration of base or local change of pH at the electrode surface. The solution contains metal salts or metal complexes. This may result in powdery or loosely adherent coatings. The cathodic electrodeposition or base generation method for synthesizing oxides was first described by Switzer [32]. The local increase in pH happens either by consumption of hydronium ions or production of hydroxide ions. Depending on the species in solution, both of these mechanisms may be occurring. The most likely reactions include [33] ... 

R.E. Ionescu, C. Gondran, L.A. Gheber, S. Cosnier, and R.S. Marks, Construction of amperometric immunosensors based on the electrogeneration of a permeable biotinylated polypyrrole film. Anal. Chem. 76, 6808-6813 (2004). 

Two types of electrogenerated carbon bases have commonly been used (1) dianions derived from activated alkenes, and (2) carbanions formed by reductive cleavage of halogen compounds or by direct reduction of weak carbon acids. In both cases, the efficiency of the proton transfer reaction relies on a thermodynamically favored proton transfer or a fast follow-up reaction of the deproto-nated substrate. 

Electrogenerated (EG) Base-Assisted Esterification of Penicillanic Acid... 

Melton et al. [452] found that the electrochemical properties of buffered melts remained identical to those of neutral melts. The buffered melts maintained their neutrality, as well as the electrochemical window, even if changes were induced in the chloroacidity by the addition or electrogeneration of a Lewis acid or base. 

One of the earliest applications of digital simulation to inorganic chemistry was for analysis of isomerization of CpCo(l,3-CgH8) to CpCo(l,5-C8Hg), which proceeds via a simple square scheme (Figure 3). Because the 1,3 and 1,5 isomers have different E1/2 values (-2.27 V and -2.51V, respectively), resolution of the two species in voltammetric curves is possible. Variation of the scan rate produces different currents for the electrogenerated species based on... 

III. SYNTHETIC UTILIZATION OF ELECTROGENERATED BASES A. Electrogenerated Nitrogen Bases... 

Two types of electrogenerated carbon bases are commonly used dianions derived from activated alkenes, and carbanions formed by cleavage or direct reduction of weak carbon acids. 

The literature in this area is often ambiguous because although carbanions are common intermediates in electrosynthesis, especially as the result of cathodic cleavage, their followup reactions include involvement as nucleophiles or as bases. Also, as we shall see, electrogenerated carbanion bases may be used to generate nucleophiles from other acidic components of the reaction mixture. A comprehensive review [53] of this topic covers both types of behavior. Here an attempt is made to concentrate on those reactions where basic behavior of the electrogenerated carbanion is paramount. 

Another technique for the formation of diethyl 1,2-epoxyalkylphosphonates is based on the reactivity of an electrochemically generated carbanion of diethyl chloromethylphosphonate in DMF toward aromatic aldehydes. The yield of 72% obtained with para-methoxybenzaldehyde is promising. However, the major disadvantage that attends the use of the electrochemical route is the difficulty that may be encountered in the electrogeneration of species sufficiently basic to deprotonate chloromethylphosphonates. 

Zorzi M, Pastore P, Magno F (2000) a single calibration graph for the direct determination of ascorbic and dehydroascorbic acids by electrogenerated luminescence based on Ru(bpy) in aqueous solution. Anal Chem 72(20) 4934-4939. doi 10.1021/ac991222m... 

Kurita R, Aral K, Nakamoto K, Kato D, Niwa O (2010) Development of electrogenerated chemiluminescence-based enzyme linked immunosorbent assay for sub-pM detection. Anal Chem 82(5) 1692-1697... 

Guillet N, Roue L, Marcotte S, Villers D, Dodelet JP, Chhim N, Trevin S (2006) Electrogeneration of hydrogen peroxide in acid medium using pyrolyzed cobalt-based catalysts influence of the cobalt content on the electrode performance. J Appl Electrochem 36(8) 863-870... 

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