M13 9PL 6oCo y-Radiation has been used to initiate the free-radical reduction reaction (i) and the mechanism is shown to be as in reactions (ii)-(iv), where reactions (ii) and (iii) are the propagating steps and reaction (iv) the terminating

In the radiolysis of oxygenated aqueous solutions of cysteine (RSH) at p H 7, short chain reactions occur yielding cystine (RSSR) and hydrogen peroxide. Two competing reaction paths involving reaction of the thiyl radical (RS.) with oxygen or thiol anion (RS-) are postulated to explain the results.

Some rate constants for the reduction of para-substituted benzenediazonium ions by the radicals eaq-, ·CH2OH, (CH3)2·COH and some semiquinone radical anions have been measured. The substituent group has no effect on the rates with eaq-, but as the reduction potential of the reducing radical becomes more positive, the substituent effect increases, electron-withdrawing groups enhancing the rates. No free halide is formed on reduction of p-BrC6H4N2+ or p-IC6H4N2+ by eaq- or ·CH2OH.

Electron-withdrawing substituents are shown to increase the chain length of free-radical hydrodediazoniation reactions, but the actual reaction step causing the substituent effect depends on the relative rates of propagation and termination reactions. With benzyl alcohol as reducing agent the rate of the slow propagation step is increased, while with isopropyl alcohol the rate of the termination step is decreased. Rate constants for some reactions of radicals with diazonium ions are reported, and the nature of some of these reactions and their implication for an understanding of the homolysis of aromatic diazo compounds are discussed.

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