Pyridine electrochemistry

Over 90% of the reported studies on pyridine electrochemistry deal with cathodic transformations. One reason for this is that the experimental techniques for studying cathodic reactions are more numerous and tractable. 

Less than 10% of the reports on pyridine electrochemistry deal with anodic reactions. The mechanisms of these reactions are rarely known and, as a result, yields or current efficiencies have not always been optimized. Many of the anodic reactions were studied in beaker cells, which are simply not good models for modern flow cells moreover, uncontrolled power supplies were often used. Consequently, anode overpolarization caused ring degradation in many cases. 

Radish KM, Shao J, Ou Z, Zhan R, Burdet E, Barhe J-M, Gros CP, Guilard R. 2005. Electrochemistry and spectroelectrochemistry of heterobimetalUc porphyrin-corrole dyads. Influence of the spacer, metal ion, and oxidation state on the pyridine binding ability. Inorg Chem 44, 9023-9038. 

Another level of permeability Is that of axial bases, such as pyridine. As noted above, we have seen the porphyrin electrochemistry to respond to addition of axial bases to the contacting solutions this implicitly demonstrates that bases such as pyridine are able to penetrate the films to the axial porphyrin sites in its interior. 

Zinc dithiocarbamates have been used for many years as antioxidants/antiabrasives in motor oils and as vulcanization accelerators in rubber. The crystal structure of bis[A, A-di- -propyldithio-carbamato]zinc shows identical coordination of the two zinc atoms by five sulfur donors in a trigonal-bipyramidal environment with a zinc-zinc distance of 3.786 A.5 5 The electrochemistry of a range of dialkylthiocarbamate zinc complexes was studied at platinum and mercury electrodes. An exchange reaction was observed with mercury of the electrode.556 Different structural types have been identified by variation of the nitrogen donor in the pyridine and N,N,N, N -tetra-methylenediamine adducts of bis[7V,7V-di- .vo-propyldithiocarbamato]zinc. The pyridine shows a 1 1 complex and the TMEDA gives an unusual bridging coordination mode.557 The anionic complexes of zinc tris( V, V-dialkyldithiocarbamates) can be synthesized and have been spectroscopically characterized.558... 

Recently, an inorganic promoter as [Ru(CN)5(Spy)]4 (Spy = 4-thio-pyridine) adsorbed on a gold electrode surface also proved to be very effective in the direct electrochemistry of cytochrome c the tetraanion not... 

It seems useful to understand the mechanisms involved in the chemistry and in the electrochemistry of sulfur and polysulfides. During the last 10 years, more than 90 papers deahng with solvothermal synthesis of chalcogenides MxE or binary chalcogenides MxM Ez (E = S, Se, or Te) have been published. In a typical process, a metal and/or a metallic salt is heated in a solvent (benzene, toluene, pyridine, ethylenediamine, water, etc.) at 100-200 ° C in the presence of an excess of chalcogen (see for instance Ref. 125). These empirical syntheses would benefit from a sound understanding of the involved mechanisms. 

The industrial and pilot plant applications of electrochemistry of pyridine derivatives will be included in a later chapter6 in this series that chapter will give a description of electrochemical cells employed in large-scale electrochemical synthesis and the problems in scaling up laboratory processes these problems are also treated in some books.7,8... 

Although the entire discussion of electrochemistry thus far has been in terms of aqueous solutions, the same principles apply equaly well to nonaqueous solvents. As a result of differences in solvation energies, electrode potentials may vary considerably from those found in aqueous solution. In addition the oxidation and reduction potentials characteristic of the solvent vary with the chemical behavior of the solvent. as a result of these two effects, it is often possible to carry out reactions in a nonaqueous solvent that would be impossible in water. For example, both sodium and beryllium are too reactive to be electroplated from aqueous solution, but beryllium can be electroplated from liquid ammonia and sodium from solutions in pyridine. 0 Unfortunately, the thermodynamic data necessary to construct complete tables of standard potential values are lacking for most solvents other than water. Jolly 1 has compiled such a table for liquid ammonia. The hydrogen electrode is used as the reference point to establish the scale as in water ... 

Whereas the first synthesis of chemicals by electrolysis dates back over 180 years, the equipment and techniques to understand the fundamentals of these reactions were not developed until recently. This review of electrochemical citations of pyridine compounds of industrial interest is keyed to the functionality of the starting pyridine hence the electrochemistry of pyridines is indexed and not their preparation by electrolysis. 

Because the electrochemistry of pyridines has not been reviewed before with regard to industrially significant processes, this review will therefore cover the period 1801-1983. Citations from 1801-1975 have been compiled in Swann s bibliography.1 These citation listings were broken down into six indices author, patent, product molecular formula, synonym, product name, and product type. A computer-aided search of Chemical Abstracts and the World Patent Index covered the period 1967-1983. Other sources such as the reviews on heterocyclic electrochemistry by Lund2 and Nelson3 contained useful citations. Nelson s review has a valuable table that summarizes the synthetic work by indexing the parent heterocycle. 

W. Flitsch and G. Jones provide the first comprehensive review of pyrrolizine chemistry, an area of increasing interest. The chemistry of the arene oxides has been brought up-to-date by G. S. Shirwaiker and M. V. Bhatt. Following the overall treatment of the electrochemistry of heterocycles given by Lund in Volume 36 of this series, J. E. Toomey has now reviewed electrochemical synthesis and modification of pyridines, a subject of great industrial and academic interest. 

Financial support was provided by the National Science Foundation (Grant CHE-94-13128). Prof. Alan Bond and Mr. Richard Webster provided advance information concerning their studies on the electrochemistry of pyridine 2,6-dithioesters and related substances84. 

Silver clusters 2.5 nm in diameter displayed unusual electrocatalytic properties in Wolff rearrangements of diazoketones.67 The reaction proceeds with electron transfer to and from the silver cluster. The presence of an a-ketocarbene/ketene was confirmed using pyridine as a nucleophilic probe and by UV-visible spectroscopy. Electrochemistry was used to support the role of the silver particles in the rearrangement. 

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