En. Step et Nj. Turro, PHOTOLYSIS OF KETONES IN OXYGEN-SATURATED MICELLAR SOLUTION - OXYGEN SCAVENGING OF C-CENTERED RADICALS IN MICROHETEROGENEOUS MEDIA, Journal of photochemistry and photobiology. A, Chemistry, 84(3), 1994, pp. 249-256
The oxygen scavenging of C-centered radicals in microheterogeneous med
ia was studied by investigation of the photolysis of several ketones (
dibenzyl ketone (DBK), o- and p-methyldibenzyl ketone (o-MeDBK and p-M
eDBK) and d,1-2,4-diphenylpentan-3-one (d,1-DPP)) in oxygen-saturated
sodium dodecylsulfate (SDS) micellar solution. The acyl- and benzyl-ty
pe radicals initially formed during the photolysis of these ketones ca
n undergo geminate micellar and random bulk aqueous recombination or c
an react with oxygen in the bulk or micellar phases to yield peroxy ra
dicals. The efficiency of radical scavenging by oxygen was calculated
on the basis of three experimental parameters, i.e. the recombination
probability fake P-r, of a primary acyl-benzyl radical pair (RP), the
secondary cage effect for benzyl-benzyl RP recombination and the chemi
cal yield of dibenzyls. Under a partial pressure of 1 atm, oxygen was
found to scavenge only those radicals which enter the bulk aqueous pha
se if the lifetime of the geminate radicals inside the micelles is rel
atively short (about 20 ns). However, for micellized geminate radicals
with a longer lifetime (about 70-80 ns), scavenging by oxygen inside
the micelles successfully competes with geminate radical recombination
. These results are compared with other investigations involving the d
ynamics and partitioning of oxygen in SDS micelles.