Electrochemical coupling reaction

Coupling reactions. Electrochemical coupling reactions with (bpy)NiBr2 catalysis include those between alkenyl bromides and a-halo esters, aryl and pyridyl halides, as well as aryl and chlorophosphines. ... 

Enzyme Immunosensors. Enzyme immunosensors are enzyme immunoassays coupled with electrochemical sensors. These sensors (qv) require multiple steps for analyte determination, and either sandwich assays or competitive binding assays maybe used. Both of these assays use antibodies for the analyte of interest attached to a membrane on the surface of an electrochemical sensor. In the sandwich assay type, the membrane-bound antibody binds the sample antigen, which in turn binds another antibody that is enzyme-labeled. This immunosensor is then placed in a solution containing the substrate for the labeling enzyme and the rate of product formation is measured electrochemically. The rate of the reaction is proportional to the amount of bound enzyme and thus to the amount of the analyte antigen. The sandwich assay can be used only with antigens capable of binding two different antibodies simultaneously (53). 

Coupling reactions and related fluoroalkylations with polytTuoioalkyl halides are induced by vanous reagents, among them metals such as copper and zinc, or by an electrochemical cell. More recently, examples of carbon-carbon bond forma tion by coupling of unsaturated fluorides have been reported Both acyclic and cyclic fluoroolefins of the type (Rp)2C=CFRp undergo reducUve dimerization on treatment with phosphines [42] (equation 33) The reaction shown in equation 33 IS also accompbshed electrocheimcally but less cleanly [43]... 

In complete galvanic cells, electrochemical reactions occur simultaneously at the anode and cathode. Since the current is of equal strength at the two electrodes, the corresponding electrode reactions are interrelated, in that the number of electrons set free in unit time at the anode is equal to the number of electrons reacting during the same time at the cathode. Electrode reactions subject to such a condition are called coupled reactions. 

Corrosion (from Latin corrodere, gnaw to pieces ) of metals is the spontaneous chemical (oxidative) destruction of metals under the elfect of their environment. Most often it follows an electrochemical mechanism, where anodic dissolution (oxidation) of the metal and cathodic reduction of an oxidizing agent occur as coupled reactions. Sometimes a chemical mechanism is observed. 

The ratio ARH/ARj (monoalkylation/dialkylation) should depend principally on the electrophilic capability of RX. Thus it has been shown that in the case of t-butyl halides (due to the chemical and electrochemical stability of t-butyl free radical) the yield of mono alkylation is often good. Naturally, aryl sulphones may also be employed in the role of RX-type compounds. Indeed, the t-butylation of pyrene can be performed when reduced cathodically in the presence of CgHjSOjBu-t. Other alkylation reactions are also possible with sulphones possessing an ArS02 moiety bound to a tertiary carbon. In contrast, coupling reactions via redox catalysis do not occur in a good yield with primary and secondary sulphones. This is probably due to the disappearance of the mediator anion radical due to proton transfer from the acidic sulphone. 

Coupling an electrochemical cell to an analytical device requires that hindering technical problems be overcome. In the last years there has been a considerable improvement in the combined use of electrochemical and analytical methods. So, for instance, it is now possible to analyze on-line electrode products during the simultaneous application of different potential or current programs. A great variety of techniques are based on the use of UH V for which the emersion of the electrode from the electrolytic solution is necessary. Other methods allow the in situ analysis of the electrode surface i.e the electrode reaction may take place almost undisturbed during surface examination. In the present contribution we shall confine ourselves to the application of some of those methods which have been shown to be very valuable for the study of organic electrode reactions. 

The reduction of organic halides is of practical importance for the treatment of effluents containing toxic organic halides and also for valuable synthetic applications. Direct electroreduction of alkyl and aryl halides is a kinetically slow process that requires high overpotentials. Their electrochemical activation is best achieved by use of electrochemically generated low-valent transition metal catalysts. Electrocatalytic coupling reactions of organic halides were reviewed in 1997.202... 

The electrochemical reduction of cycloheptatriene (CHT) in liquid ammonia takes place at about —2.5 V vs SCE and forms the radical anion of CHT. The radical anion is stable in ammonia on the voltammetric time scale but decays slowly by disproportionation and coupling reaction pathways to give respectively 1,3- and 1,4-cycloheptadienes (total yield 34-39%) and C14H18 (in yields of 55-58%) isomers which incorporate the bitropyl carbon skeleta20. 

The quantities a, z, n can be determined separately, so that Eq. (11.32) offers an alternative way of obtaining the electrochemical reaction orders. A good discussion of the coupling of electrochemical with chemical reactions has been given by Parsons [1]. 

Reetz, M.T., Quaiser, S.A., and Merk, C., Electrochemical preparation of nanostructured titanium clusters characterization and use in Mcmurry-type coupling reactions, Chem. Ben, 129, 741, 1996. 

Perhaps the best-known and most widely appreciated electrochemical transformation is the Kolbe oxidation (see also Chapter 6) [1, 2, 31]. The process involves the one electron oxidation of the salt of a carboxylic acid, and the loss of carbon dioxide to afford a radical, R, that subsequently engages in coupling reactions. Both symmetrical (R + R ) and nonsym-metrical (R + R ) radical couplings are known and are illustrated in the following discussion. The nonsymmetrical variety (often referred to as a mixed or hetero coupling) is remarkable given that it requires the cogeneration and reaction of more than one reactive intermediate. 

Organic Electroreductive Coupling Reactions using Transition Metal Complexes as Catalysts Table 17. Electrochemical carboxylation of alkynes in the presence of Ni(bipy)3(BF4)2... 

A fundamental fuel cell model consists of five principles of conservation mass, momentum, species, charge, and thermal energy. These transport equations are then coupled with electrochemical processes through source terms to describe reaction kinetics and electro-osmotic drag in the polymer electrolyte. Such convection—diffusion—source equations can be summarized in the following general form... 

Based on Knochel s work59, which has employed cobalt halides as catalyst for the acylation of dialkylzinc reagents into ketones, this catalyst has been investigated for the coupling reaction of electrochemical arylzinc compounds formed in acetonitrile (equation 71)60. 

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