Oxidation reduced metals, source

The alkylation of quinoline by decanoyl peroxide in acetic acid has been studied kineti-cally, and a radical chain mechanism has been proposed (Scheme 207) (72T2415). Decomposition of decanoyl peroxide yields a nonyl radical (and carbon dioxide) that attacks the quinolinium ion. Quinolinium is activated (compared with quinoline) towards attack by the nonyl radical, which has nucleophilic character. Conversely, the protonated centre has an unfavorable effect upon the propagation step, but this might be reduced by the equilibrium shown in equation (167). A kinetic study revealed that the reaction is subject to crosstermination (equation 168). The increase in the rate of decomposition of benzoyl peroxide in the phenylation of the quinolinium ion compared with quinoline is much less than for alkylation. This observation is consistent with the phenyl having less nucleophilic character than the nonyl radical, and so it is less selective. Rearomatization of the cr-complex formed by radicals generated from sources other than peroxides may take place by oxidation by metals, disproportionation, induced decomposition or hydrogen abstraction by radical intermediates. When oxidation is difficult, dimerization can take place (equation 169). 

Inorganic sources include naturally occurring ores, as well as manufactured products that include oxides and metallic salts such as sulfates, chlorides, and nitrates. After grinding, the tri- and tetravalent oxides may be roasted in a kiln and reduced to divalent forms. 

In both the electrorefining (ER) and electrowinning (EW) processes, the primary product is a pure cathode sheet. Although similar processes, ER and EW differ only in the source of the metal ions that are reduced at the cathode. In electrorefining, impure, solid metal anodes are suspended in the electrolytic cell and oxidized to metal ions by the current. The metal ions are, in turn, reduced at the cathode. The net result is that metal ions are formed at the anode and removed at the cathode. Nickel, copper, and other metals can be cast in the impure form as anodes, which serve as the metal ion source during electrorefining. 

To show that the source of the amino acids in our experiments was not the result of the reaction of the various nitrogen species produced in the reaction with ascorbic acid, we reacted ascorbate individually and in combination with ammonia, hydrazine, nitrite, and nitrate. Very low traces of amino acids were produced in these reactions, indicating that the amino acids detected are in fact produced from the electric discharge reaction. While ascorbic acid is not likely to have been an abundant prebiotic species, oxidation could have been inhibited by other available chemical species such as sulfides and reduced metal ions. 

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