A Comparative Study of Homolytic Reactions of Fullerenes with Aldehydes in a Mass Spectrometer under Electron Impact and in Solution under UV Irradiation

Abstract

C60 was reacted in the ionization chamber of a mass spectrometer under electron impact (EI) with aldehydes, RCHO (R = Ph, p-FC6H4, F5C6, p-MeOC6H4, α-thienyl, o-HOC6H4, o-BrC6H4, m-BrC6H4 and t-Bu), with the transfer of R• radicals and with Me•-transfer from i-PrCHO and t-BuCHO. Paramagnetic fullerene derivatives were stabilized by the addition of the next R• radical or a hydrogen atom, or hydrogen or bromine atom loss. A detailed study showed that the reaction between C60 and PhCHO occurred via a homolytic mechanism that matches one reported earlier for the reaction with acetone. This suggests the generality of the mechanism for the reactions of fullerenes with other species in ionization chambers under EI at ca 300°C. All aldehydes, except one, had radicals at the carbonyl group which were different from those in the ketones examined earlier in the reactions. This expanded the variety of radicals which can be transferred to fullerenes during reactions in ionization chambers under EI. Due to this and the hydrogen atom at the CO group of aldehydes, some reactions occurred that were not found for the ketones: the formation of cyclic products C60COC6H4 and C60OC6H4 for PhCHO, o-BrC6H4CHO and o-HOC6H4CHO, respectively, and HC60Ph for o- and m-BrC6H4CHO. The reaction with α-formylthiophen gives the first example of transferring an aromatic heterocyclic radical to C60 in an ionization chamber under EI. C70 reacted with PhCHO, p-FC6H4CHO and i-PrCHO similarly to C60. The results for the reactions of C60 with PhCHO and with i-PrCHO were compared with those in solution under UV irradiation. Incomplete but reasonable coincidence was found; in both modes, the addition of Ph•, PhCO• and Me• radicals to C60 occurred, whereas some other products were formed in solution and the explanation is given as to why this occurred. This conformity sup ports the hypothesis based on the results of kindred reactions with ketones and organomercurials: the results of EI-initiated homolytic reactions between fullerenes and other compounds in an ionization chamber can predict the reactivity of the fullerenes toward them in solution.