Mechanisms direct oxide reduction reaction

Although the exact chemical mechanism for the direct oxide reduction reaction has not yet been fully characterized, it has been well established that the reaction goes to completion when excess calcium is present, sufficient CaCl2 is available to dissolve the CaO produced, and adequate stirring is used. As calcium metal is soluble to about 1 wt% in CaC12 at 835°C, excess Ca insures that the reaction is driven to completion by mass-action effects. 

These results may easily be rationalized by assuming that the formation of hydroxy sulphoxides 91, 92 and 93 from hydroperoxysulphides 89 and 90 is an intramolecular oxidation-reduction reaction proceeding through a five-membered transition state 94. However, an alternative intermolecular mechanism in which the approach of the oxidant is directed by the hydroperoxy or the hydroxy function in the reductant cannot be excluded. 

In Part 2 of this book, we shall be directly concerned with organic reactions and their mechanisms. The reactions have been classified into 10 chapters, based primarily on reaction type substitutions, additions to multiple bonds, eliminations, rearrangements, and oxidation-reduction reactions. Five chapters are devoted to substitutions these are classified on the basis of mechanism as well as substrate. Chapters 10 and 13 include nucleophilic substitutions at aliphatic and aromatic substrates, respectively, Chapters 12 and 11 deal with electrophilic substitutions at aliphatic and aromatic substrates, respectively. All free-radical substitutions are discussed in Chapter 14. Additions to multiple bonds are classified not according to mechanism, but according to the type of multiple bond. Additions to carbon-carbon multiple bonds are dealt with in Chapter 15 additions to other multiple bonds in Chapter 16. One chapter is devoted to each of the three remaining reaction types Chapter 17, eliminations Chapter 18, rearrangements Chapter 19, oxidation-reduction reactions. This last chapter covers only those oxidation-reduction reactions that could not be conveniently treated in any of the other categories (except for oxidative eliminations). 

We have stressed the direct relationship of specific nutritional needs to enzyme building, but this is only one possibility. In the case of nicotinamide, for example, which in the form of coenzymes I and II functions in oxidation-reduction reactions, an individual s need may be great because of the genetic ineffectiveness of the mechanism for building nicotinamide into enzyme systems, but the difficulty may lie at another site. Possibly there is difficulty in digestion (of the combined forms) or more likely absorption, which precludes the individual from getting a substantial portion of the nicotinamide out of his food to the cells that need it. Even the mechanism for transport may be at fault. We wish to emphasize that the effectiveness or ineffectiveness of the structures and mechanisms which may be... 

Site-specific inhibitors of electron transport shown using a mechanical model for the coupling of oxidation-reduction reactions. [Note Figure illustrates normal direction of electron flow.]... 

Marcus LFER. Oxidation-reduction reactions involving metal ions occur by (wo types of mechanisms inner- and outer-sphere electron transfer. In the former, the oxidant and reductant approach intimately and share a common primary hydration sphere so that the activated complex has a bridging ligand between the two metal ions (M—L—M ). Inner-sphere redox reactions thus involve bond forming and breaking processes like other group transfer and substitution rcaclions, and transition-state theory applies directly to them. In outer-sphere electron transfer, the primary hydration spheres remain intact. The... 

Meinwald and coworkers71 studied the chemistry of naphtho[l, 8-bc]thiete and its S-oxides. The reaction of the sulphone 2 with LAH (equation 29) is of particular and direct relevance to this section since it is different from the reductions that have been discussed thus far, because the major reaction pathway is now cleavage of an S—C bond, rather than a deoxygenation of the sulphur atom. The major product (equation 29) was isolated in 65% yield two minor products accounted for a further 15% yield. One of the minor products is 1-methylthionaphthalene and this was most probably produced by an initial reduction of the strained 1,8-naphthosulphone, 2, to the thiete, which was then cleaved to the thiol and subsequently methylated. Meinwald also showed71 that the thiete was subject to cleavage by LAH as well as that both molecules were susceptible to attack and cleavage by other nucleophiles, notably methyllithium. These reactions are in fact very useful in attempts to assess a probable mechanism for the reduction of sulphones by LAH and this will be discussed at the end of this section. 

We have developed the efficient synthesis of the SERM drug candidate 1 and successfully demonstrated the process on a multiple kilogram scale to support the drug development program. A novel sulfoxide-directed borane reduction of vinyl sulfoxides was discovered. The mechanistic details of this novel reaction were explored and a plausible mechanism proposed. The sequence of asymmetric oxidation of vinyl sulfoxides followed by stereospecific borane reduction to make chiral dihydro-1,4-benzoxathiins was applied to the asymmetric synthesis of a number of other dihydro-1,4-benzoxathiins including the sweetening agent 67. 

These processes can occur by a direct electron transfer reaction to (reduction) or from (oxidation) the present organic pollutant, or by a chemical reaction of the pollutant with previously electrogenerated species. The mechanism is generally viewed as a direct anodic oxidation of organic pollutant involving its reduction by direct electron transfer from organic molecule to the electrode to form a radical cation that readily deprotonates, equation (37) ... 

Both reacting intermediates, TPrA and Ru(bipy)33 + species, are produced simultaneously during electrochemical oxidation Actual ECL mechanism, however, is somewhat more complicated than expressed by the above reaction pattern with ECL emission from Ru(bipy)32+/TPrA system depending on the applied electrode potential. Usually, the direct oxidation of TPrA at the electrode occurs at more negative potentials than characteristic for the Ru(bipy)32+/Ru(bipy)33 + redox couple. Generally, the ECL emission from Ru(bipy)32+/TPrA system as a function of applied potential consists of two emission waves (both associated with the emission from 3 Ru(bipy)32 + ) attributed to TPrA and Ru(bipy)32 + oxidation, respectively.154 First emission wave corresponds to annihilation of sufficiently stable TPrA + (with half-life of 0.2 ms) and Ru(bipy)3 + species with Ru(bipy)3 + intermediate formed from the reduction of Ru(bipy)32+ by TPrA free radical ... 

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