Free radicals from alkylbenzenes

The free-radical reaction may be equally initiated by photoactivated sulfur dioxide (3S02)442 (equation 79). On the other hand, polysulfones are obtained by radical copolymerization of appropriate olefins with sulfur dioxide443-449, and similarly, uptake of sulfur dioxide by a radical-pair formed by nitrogen extrusion from an azo compound yields the corresponding sulfone450 (equation 80). Correspondingly, alkylbenzenes, dibenzoyl peroxide, and sulfur dioxide yield sulfones under thermal conditions451... 

In contrast to oxidations with Mn(III) acetate, the oxidation of alkylbenzenes by the stronger oxidant, Co(III) acetate, appears to involve only electron transfer. No competition from classical free radical pathways is apparent. Waters and co-workers,239,240 studied the oxidation of a series of alkylbenzenes by Co(III) perchlorate in aqueous acetonitrile. They observed a correlation between the reactivity of the arene and the ionization potential of the hydrocarbon which was compatible with the formation of radical cations in an electron transfer process. 

Maleic anhydride reacts with alkylbenzenes in the presence of free radicals to form adducts of Type I and with benzene, chlorobenzene, and alkylbenzenes under photochemical excitation to form adducts of Type II. In this study solutions of maleic anhydride in benzene, toluene, ethylbenzene, and cumene were exposed to high frequency (3.6 and 8.0 kc./ sec.) electric discharge in an atmosphere of N2 or He. Adducts of Type II were isolated in yields ranging from 8 to 23% of the converted maleic anhjydride. The balance was made up of adducts of Type I together with products of higher condensation with maleic anhydride. The product distribution suggests that most of the active species in the present system are excited molecules and not free radicals. 

As in the free-radical halogenation of alkanes, chlorination of alkylbenzenes is less selective than bromination. Given the relative rates per hydrogen for hydrogen atom abstraction from 1-phenylbutane by chlorine for the elementary step shown, calculate the percentage of 1-chloro-1-phenylbutane in the C10H13CI product. 

Electron-transfer reactions are normally performed in polar solvents such as acetonitrile (MeCN), in which the product ions of the electron transfer are stabilized by the strong solvation [6,7]. When a cationic electron acceptor (A ) is employed in electron-transfer reactions with a neutral electron donor (D), the electron transfer from D to A+ produces a radical cation (D +) and a neutral radical (A ). In such a case, the solvation before and after the electron transfer may be largely canceled out when the free-energy change of electron transfer is expected to be rather independent of the solvent polarity. The solvent independent value is confirmed by determination of the Eqx values of alkylbenzene derivatives (electron donors) and Ered values of acridinium cations (electron acceptors) in solvents with different polarities [79]. The E°ox values of alkylbenzene derivatives in a less polar solvent (CH2CI2) are shifted to the positive direction by about 0.1 V... 

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