Ferrocyanide-peroxide mixtures

Subsequent work (84) confirmed these ideas. The addition of oxidized aquo salt to ferrocyanide-peroxide mixtures has the same effect as the same concentration of the reduced form, as it should. Further, addition of cyanide, nitrite, or nitrosobenzene to both illuminated ferrocyanide solutions and to ferrocyanide containing aquopentacyanoferrate, suppresses the catalytic decomposition. This effect is due to the reversal of the equilibrium (I) by a higher cyanide concentration, and to the removal of aquo salt by nitrite and nitrosobenzene to form the complex ions [Fe(CN)5N02]"" and [Fe(CN)6ONPh],/, respectively, reactions which are known to occur readily. It is also suggested (85) that even the catalytic decomposition by ferrocyanide in the dark is due to a small amount of aquopentacyanoferrite in purely thermal (as opposed to photochemical) equilibrium with ferrocyanide according to (I). 

The above compensating reactions are attractive because of the success of similar schemes in the halide catalysis, but proof in this case is more difficult. Thus it was possible to show in the halide systems that halogen and halide are present simultaneously. Evidence for the presence of ferrous ion in the ferric catalysis would support a similar interpretation. Manchot and Lehmann (44) claimed to have proved that ferrous ion is formed from ferric ion in the presence of peroxide since the addition of <, < -dipyridyl to the mixture resulted in the slow formation of the red ferrous tris-dipyridyl ion Fe(Dipy)3++. However, later work (65,66), which will be discussed when these systems are considered in more detail (IV,6), indicates that the ferrous complex ion may be formed by reduction not of the ferric ion, but of a ferric dipyridyl complex. Similar conclusions on the presence of ferrous ion were drawn by Simon and Haufe (67) from the observation that on addition of ferri-cyanide to the system Prussian blue is formed. This again is ambiguous, since peroxide is known to reduce ferricyanide to ferrocyanide and the latter with ferric ion will of course give Prussian blue (53). 

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