Effect of the medium on the reactivity of fullerene N60 with respect to the peroxide radicals RO2 ·. Chemiluminescence in the C60—AIBN—O2—C2H5Ph—PhH system

Abstract

Chemiluminescence (CL), HLPC, and volumetry were used to demonstrate that fullerene С 60 exerts no inhibiting effect on the liquid phase chain oxidation of hydrocarbons. Peroxide radicals RO 2 • do not add to С 60 in hydrocarbons with active C-H bond, because the reaction is suppressed by the competing addition of RO 2• to the hydrocarbon. The addition of RO 2 • radicals to С 60 does occur in benzene (a solvent with strong C-H bonds) in the presence of low concentrations of the hydrocarbon oxidized. Fullerene С 60 is found to exhibit a new type of liquid phase CL, which is presumably generated upon thermal decomposition of fullerene peroxides formed by adding peroxy radicals to fullerene in the C 60 -AIBN-O 2 -C 2 H 5 Ph-PhH system. The CL spectrum exhibits long wavelength maxima at 645 and 685 nm. The supposed CL emitters are keto derivatives of fullerene С 60 .There are two main reasons which make investigations of the reactivity of fullerene С 60 to the peroxide radicals RO 2 • topical. First, RO 2 • radicals are key intermediates of numerous chemical and biochemical oxidation process es. Second, there are contradictory data 1-7 (we have dis cussed them in quite detail earlier 1 ) on the ability of ful lerene to act as inhibitor by reaction (1) in thermal oxida tive degradation of polymers 2-4 and in reactions involved in the metabolism of viruses and pathogenic bacteria. 5-7 RO 2 • + C 60 P(1) P -productsHowever, our chemiluminescence (CL) and HPLC study 1 revealed no inhibiting effect of С 60 fullerene on AIBN initiated liquid phase oxidation of various hydro carbons including ethylbenzene (EB), dodecane, and cy clohexane and oleic acid. It was concluded 1 that С 60 does not react with RO 2 • radicals. However, more recently it was found 8 that peroxide radicals (Bu t O 2 • generated upon catalytic decomposition of Bu t OOН) add to С 60 yielding a complex fullerene peroxide (Bu t OO) x C 60 (O) (x = 4) con taining one epoxide oxygen. It is important that the sol vents used in Ref. 1 were hydrocarbons with a fairly strong C-H bond (cf. benzene, 8 which is much less active in proton donation). In this connection, it seems likely that the lifetime of peroxide radicals RO 2 • in benzene is much longer than in the solvents containing active hydrogen; therefore, reaction (1) in benzene is much more probable. The aim of this work is to explore the effect of the medium on the reactivity of fullerene toward RO 2 • radicals by com paring some parameters of two pairs of redox systems, С 60 -AIBN-O 2 -C 2 H 5 Ph-DBA (DBA is 9,10 di bromoanthracene) and AIBN-O 2 -C 2 H 5 Ph-DBA, С 60 -AIBN-O 2 -C 2 H 5 Ph-PhH and AIBN-O 2 --C 2 H 5 Ph-PhH. In addition, we tried to detect CL in the system С 60 -AIBN-O 2 -C 2 H 5 Ph-PhH. ExperimentalCommercially available fullerite was used, its purity (С 60 , 99.8%) was assessed by HPLC and elemental analysis. Benzene and EB (both "chemically pure" grade) were used as received, AIBN and DBA ("pure" grade) were recrystallized as described in Ref. 9. Solutions of С 60 were prepared by disso...

Density Functional Theory Study on the Decay of Fullerenyl Radicals RC60•, ROC60•, and ROOC60• (R = tert-Butyl and Cumyl) and Polarizability of the Formed Fullerene Dimers

“…Another important issue of fullerene radical chemistry deals with ability of C 60 and its derivatives to inhibit radical processes in chemical and biochemical systems. , For example, effects of fullerene on the liquid-phase oxidation of hydrocarbons − and lipids, radical polymerization (see ref and references therein), and thermo-oxidative destruction of the fullerene-containing polymers , have been previously studied. Different radical particles can act as intermediates of the processes listed above: these are alkyl R • , alkoxy RO • , and peroxy radicals ROO • .…”

“…Thus, there are at least three alternative routes of fullerenyl radical decay. For simplification, we have excluded reactions of cross-addition, when different radicals are attached to one fullerene core, and reactions of fullerenyl radicals with the solvent (this is close to the experimental fullerene-containing systems with nonreactive medium, e.g., benzene 11 ). We can propose that formation of 1,2-and 1,4-bisadducts in "C 60 + X • " systems should be thermodynamically more favorable than the dimerization due to the observed reversibility of the last one.…”