Dissociative Electron Capture and Related Reactions

The hydrated electron reacts with many compounds which are capable of releasing an anion by dissociative electron capture [e.g., reaction (8)], and, among others, it was this property which allowed the differentiation between eaq and H [reactions (9) and (10)] (Armstrong et al. 1958 Hayon and Allen 1961 Jortner and Rabani 1962). 

The alternative of using H202 [reaction (11) k = 1.3 x 1010 dm3 mol-1 s 1] instead of N20 may lead to complications, since H202 also reacts with OH, II and many other radicals (Chap. 6). 

In their reactions with tertiary butylhydroperoxide, H and eaq show a different selectivity (Phulkar et al. 1990). While H undergoes reactions (12) and (13) with about equal probability, i.e both fBuO and OH are formed, eaq yields only fBu() [reaction (14)]. This preference in splitting the peroxidic bond is due to the much higher solvation energy of the hydroxide compared to the tertiary butoxide ion. For a detailed study on the reaction of H with H202 see Mezyk and Bartels (1995). 

With thiols, eaq- reacts predominantly by dissociative ET [reaction (15)], but also formation of molecular hydrogen [reaction (16)] is observed (Hoffman and Ha-yon 1973). As one might expect, there is a considerable drop in the rate constant when the thiol group is deprotonated (for a systematic study, see Mezyk 1995). 

In a number of reactions that are written as dissociative electron attachments, short-lived radical anions are in fact intermediates. A case in point is 5BrUra (Chap. 10). An interesting behavior is shown by the radical anion of N-bromo-succinimide which does not release a bromide ion but rather fragments into a bromine atom and a succinimide anion [reactions (17) and (18)] (Lind et al. 1991). 

---