Atom Transfers in Redox Reactions

In the most rudimentary sense, redox reactions are electron transfers in which the oxidant gains electrons and the reductant loses them. Yet, 

We have seen, for example (p. 80), that oxidation of SO72 by ClOj involves the transfer of an oxygen atom from chlorate to sulfite that is, the reaction is a nucleophilic substitution by sulfite on one of the oxygen atoms of chlorate. 

In much the same way the reaction of sulfite with oxygen-labeled Mn02 yields oxygen-labeled sulfate, with the label diluted fourfold, showing that one oxygen in every four in the resulting sulfate came from Mn02, rather than from some other source. 

These redox reactions, in which oxygen transfer occurs, involve changes of two units in the oxidation numbers of reactant and product. One-electron redox reactions may occur with the transfer of a halogen. The reaction between Cr+2 and Fe 3, for example, is strongly catalyzed by added chloride ion and when chloride is added to the reaction mixture, the resultant Cr(III) is present as (BUO CrC 2. It might be suggested that Cl becomes attached to Cr+a after the redox has occurred, but this cannot be. In the first place, independent experiments show that under these conditions the reaction between Cr+3 and Cl is very slow second, chloride attachment after the redox has occurred would not explain the catalytic role of chloride. It is more likely that the reaction occurs via a chloride-bridge transition state, and that the redox is accomplished by a chlorine transfer  

More than one atom may be transferred in a redox reaction. In the reduction of (NH3) Co(SCN)+2 with Cr+2, one SCN becomes bonded to each Cr(III) in the product  

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