Platinum sulfite oxidation

Geminal dihalides undergo partial or total reduction. The latter can be achieved by catalytic hydrogenation over platinum oxide [512], palladium [512] or Raney nickel [63, 512], Both partial and total reduction can be accomplished with lithium aluminum hydride [513], with sodium bis(2-meth-oxyethoxy)aluminum hydride [514], with tributylstannane [503, 514], electro-lytically [515], with sodium in alcohol [516] and with chromous sulfate [193, 197]. For partial reduction only, sodium arsenite [220] or sodium sulfite [254] are used. 

By media variables we mean the solvent, electrolyte, and electrodes employed in electrochemical generation of excited states. The roles which these play in the emissive process have not been sufficiently investigated. The combination of A vV-dimethylformamide, or acetonitrile, tetra-n-butylammonium perchlorate and platinum have been most commonly reported because they have been found empirically to function well. Despite various inadequacies of these systems, however, relatively little has been done to find and develop improved conditions under which emission could be seen and studied. Electrochemiluminescence emission has also been observed in dimethyl sulfite, propylene carbonate, 1,2-dimethoxyethane, trimethylacetonitrile, and benzonitrile.17 Recently the last of these has proven very useful for stabilizing the rubrene cation radical.65,66 Other electrolytes that have been tried are tetraethylam-monium bromide and perchlorate1 and tetra-n-butylammonium bromide and iodide.5 Emission has also been observed with gold,4 mercury,5 and transparent tin oxide electrodes,9 but few studies have yet been made1 as to the effects of electrode construction and orientation on the emission character. 

Oxidized sulfur species occurring in natural waters (sulfate, sulfite, thiosulfate] do not interact with the platinum electrode when in the presence of H2S and the pH-Eh-E52- relations found were similar to the above relations. Thus, the unambiguous relations found between pH, Eh and E22- in aqueous solutions of hydrogen sulfide can be employed to characterize solutions and water samples where hydrogen sulfide is the only reduced sulfur species present. 

The phenomena observed m the anodic oxidation of sulfite to di-thionate are essentially similar to those described above for thiosulfate in the former case, however, there is always a considerable formation of sulfate, and when the conditions are such that the production of dithionate is suppressed, the amount of sulfate increases. Because of the strong reducing properties of sulfite, the oxidation of the platinum anode occurs less readily than in thiosulfate solution and hence larger currents are necessary for the second stage of potential to set in. 

Sulfur occurs in the valency states —2 (sulfide S ), 0 Elemental sulfur S ), +3 (dithionite S204 ), +4 (sulfite SOj ", disul-fite S205 ), also in many organic molecules), and +6 (sulfate S04 ) the most stable states are —2 and +6. Sulfur is very reactive, and reacts with most elements except iodine, gold, platinum, and the noble gases. In humid air it is slowly oxidized to traces of SO2 and H2SO3, ignites... 

Both reactions require close pH control and the completeness of the processes is determined by measuring the redox potential of the CI2/CI couple at a platinum electrode. When all cyanide has been entirely oxidized the redox potential of the solution is determined by the CI2/CI couple. Chromate ions in the process effluents can also be eliminated by reducing them to chromium(in) by sulfite ions ... 

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