Formylmethyl and formylmethylperoxyl radicals and their chlorinated derivatives. Formation and reactions in irradiated aqueous solutions

The formylmethyl radical, (CH2CHO)-C-., is known to act as an oxidant. For comparison, the chlorinated analogues, (CCl2CHO)-C-. and (CCl2CClO)-C-., were produced in irradiated aqueous solutions and their oxidation reactions studied. The radicals were produced by reaction of (OH)-O-. with trichloroethanol (CCl3CH2OH) or tetrachloroethylene (CCl2=CCl2) followed by elimination of HCl. CCl3CH2OH reacts with OH radicals, with rate constants of 1.5 x 10(8) L mol(-1) s(-1) at pH 6.6 and 1.9 x 10(9) L mol(-1) s(-1) at pH 11.4, at which the compound is partially ionized (pK(a)=12.2). These reactions take place by hydrogen abstraction to yield CCl3CHOH or CCl3CHO-, which rapidly eliminate HCl or Cl- to form the (CCl2CHO)-C-. radical. Parallel experiments with trifluoroethanol indicated formation of the CF3CHOH radical which does not eliminate HF. This radical reduces methylviologen (MV(2+), 1,1'-dimethyl-4,4'-bipyridinium dication) slowly in acidic solutions but very rapidly in alkaline solutions. From the pH effect on the rate constant, a pK(a) value of 6.0 was determined for the acid dissociation of CF3CHOH into CF3CHO-. The (CCl2CHO)-C-. radical is an oxidizing species, which reacts with ascorbate, ABTS(2-) [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate ion)], and phenolate ions somewhat more slowly than (CH2CHO)-C-.. Tn contrast, (CCl2CClO)-C-. reacts with the same compounds much more rapidly than (CH2CHO)-C-.. All three formylmethyl radicals react with O-2 to yield peroxyl radicals, The peroxyl radicals derived from the chlorinated formylmethyl are stronger oxidants than their parent species, but the peroxyl radical derived from the unchlorinated formylmethyl is a weaker oxidant than its parent species. Peroxyl radicals were also produced by the reaction of e(aq)(-) with CCl3CH2OH and with chloral hydrate in aerated solutions. These radicals, (OOCCl2CH2OH)-O-. and (OOCCl2CH)-O-.(OH)(2), are highly reactive oxidants.