Reducing agents, oxidation-reduction potentials

There is compelling evidence that reducing agent oxidation and metal ion reduction are, more often than not, interdependent reactions. Nonetheless, virtually all established mechanisms of the electroless deposition fail to take into account this reaction interdependence. An alternative explanation is that the potentials applied in the partial solution cell studies are different to those measured in the full electroless solution studies. Notwithstanding some differences in the actual potentials at the inner Helmholtz plane in the full solution relative to the partial solutions, it is hard to see how this could be a universal reason for the difference in rates of deposition measured in both types of solution. 

Several workers have shown that a high concentration of ascorbic acid added to liquid milk inhibits oxidation. Chilson (1935) suggested that added ascorbic acid acts as a reducing agent, which is oxidized more readily than milk fat. Bell et al. (1962) suggested that addition of L-ascorbic acid to cream produced a medium less conducive to oxidation by lowering the oxidation-reduction potential. Addition of an adequate level of surface-active ascorbyl palmitate to milk products may retard lipid oxidation by orientation at the lipid-aqueous interface where it intercepts free radicals (Badings and Neeter, 1980). 

Arsenic(III), antimony(III), and tin(II) ions can be oxidized to arsenic(V), antimony(V), and tin(IV) ions respectively. On the other hand, the latter three can be reduced by proper reducing agents. The oxidation-reduction potentials of the arsenic(V)-arsenic(III) and antimony(V)-antimony(III) systems vary with pH, therefore the oxidation or reduction of the relevant ions can be assisted by choosing an appropriate pH for the reaction. 

The Co(bipy)3+ ion is a useful catalyst for a number of borohydride reductions, e.g., organic nitro compounds are reduced smoothly to amines at pH 6.5-7 the true reducing agent is Co(bipy)3+. The oxidation-reduction potential for Co(I)/Co(II) is 0.91 volt (vs. standard calomel electrode in 50% aqueous ethanol) and this should fall between the potentials of the other reactants (709). Catalytic reductions of organic halogen compounds may be achieved (436), and the system is reactive to small molecules such as NgO (38). 

The exact mechanism of toxicity has not been elucidated, although there is a lot of information on how sulfur-based compounds are detoxified by the liver. Sodium sulfite is a mild reducing agent that would most likely cause burning or irritation at the site of exposure or application by altering oxidation-reduction potential and pH. 

Pentaralent neptunium is the most stable state in solution. It hydrolyzes only in basic solutions, disproportionates only at high acidity, and forms no polynuclear complexes. As shown by the oxidation-reduction potentials of Table 9.6, hexavalent neptunium is much less stable in solution than is hexavalent plutonium in fact, hexavalent neptunium is a strong oxidizing agent and is easily reduced in the presence of oxidizable substances, such as those present in ion-exchange and solvent extraction separations [K2]. 

The sensory impression of oxidation or reduction in wine indicates abnormal development. This is linked to the presence of an oxidizing (oxygen) or reducing agent, and is also related to the buffer capacity that protects wines to varying degrees from sharp variations in their oxidation-reduction potential. 

Figure 14. Oxidation-reduction titration curves of three reducing agents, showing midpoint potential Eq.

To an ordinary observer like the present writer, it has seemed curious from the beginning that a reducing agent like ascorbic acid could assist in the chemical conversion of cholesterol into 11-oxysteroids, since this is an oxidative process— though the biochemists seem to be able to explain such things by juggling with oxidation-reduction potentials ... 

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