A-hydroxyalkylperoxyl radicals

The rate of H02 elimination from a-hydroxyalkylperoxyl radicals strongly depends on the flanking substituents that also govern the strength of the resulting C-0 double bond (for a compilation see von Sonntag and Schuchmann 1997). 

The peroxyl radical anion formed in reaction (10) has an immeasurably short ( 10 6 s ) lifetime, i.e ku is much larger than k 0 x [H20], and even at high [OH ] the rate of acetone formation is essentially given by kw x [OH ] (Bothe et al. 1977). The situation is similar for other a-hydroxyalkylperoxyl radical anions (Rabani et al. 1974 Ilan et al. 1976 Bothe et al. 1983) with the exception... 

Experiments are often and carried out in the presence of buffer. Thus, it is important to note that the 02 -elimination of a-hydroxyalkylperoxyl radicals is not only induced by OH but also by buffer, albeit with a much lower rate constant [1-hydroxyethylperoxyl radical /t(OH) = 4 x 109 dm3 mol1 s 1 k(HP042 ) = 4 x 106 dm3 mol1 s Bothe et al. 1983]. 

In peroxyl-free-radical chemistry, H02702 " elimination reactions play a major role (Chap. 8.4). In polymer free-radical chemistry, these reactions are of special interest, because they lead to a conversion of slowly diffusing polymer-derived radicals into the readily diffusing HCV/CV radicals. The H02 /02 "-elimina-tion typically proceeds from an a-hydroxyalkylperoxyl radical [reaction (22)]. In poly(vinyl alcohol), for example, such an structural element is formed by H-abstraction and subsequent 02 addition [reactions (18) and (19)]. The same structural element may also be formed during the bimolecular decay of peroxyl radicals which carry an H-atom in [3-position [reactions (20) and (21)]. 

The carbon-centered radicals generally react very fast with oxygen [e.g. reaction (37)], so that under conditions of air saturation many of the elimination reactions discussed above are forestalled. This gives rise to the corresponding peroxyl radicals (for reviews on peroxyl radicals in aqueous solution see [62, 63]). Among them, the a-hydroxyalkylperoxyl radicals stand out, one, because they outnumber the others, and two, because this kind of radical is known relatively easily to eliminate H02 [eg. reaction (38)]. 

Bothe, E., Schuchmann, M. N., D. Schulte-Frohlinde, and C. von Sonntag. 1978. HOO elimination from a-hydroxyalkylperoxyl radicals in aqueous solution. Photochem. Photobiol. 28 639-644. 

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