Radical cations from 2-methylnaphthalene

The latter result is particularly interesting because it contrasts so vividly with the chemistry observed in homogeneous solution. With a homogeneously dispersed single electron photoacceptor, 1-methoxynaphthalene gives the same product as that formed in Ti02, but 1-methylnaphthalene gives a completely different product, that derived from exclusive side chain activation by radical cation deprotonation, eq. 94 (290) ... 

Toluene, durene, hexamethylbenzene, 1- and 2-methylnaphthalenes are oxidized to the corresponding benzaldehydes by irradiation in oxygen-equilibrated acetonitrile sensitized by 1,4-dicyanonaphthalene, 9-cyano-, 9,10-dicyano-, and 3,7,9,10-tetracyanoanthracene. The reaction involves proton transfer from the radical cation of the donor to the sensitizer radical anion or the superoxide anion, to yield the benzyl radical which is trapped by oxygen. In the case of durene, some tetramethylphthalide is also formed with this hydrocarbon it is noteworthy that the same photosensitization, when carried out in an nonpolar medium, yields the well-known singlet oxygen adduct, not the aldehyde [227,228] (Sch. 20). 

The selection of one preferred route for dark secondary reactions from photogenerated cation radicals can also be seen in the products derived from 1-methylnaphthalene. Although ring cleavage is observed on irradiated Ti02 suspensions, side-chain oxidation of the corresponding radical cation takes place in homogeneous solution (Eq. 6) [61]. 

Eberson and Radner (19-23) have explored some of the scope of the reaction of N02 with ArH +. They prepared the solid hexafluorophosphates of the naphthalene cation radical and some methylnaphthalene cation radicals, for example, C10H8,+PF6, and carried out reactions of the solid salts with N02 in dichloromethane at temperatures near-25 °C (19-23). Reaction was found to occur according to equation 12. The results of their reactions are summarized in Table I (19). This table also lists the results of nitrating the parent hydrocarbons by the conventional route (N02 + ) and with N204. The results prompted Eberson and Radner to dismiss the possibility that conventional nitration of these compounds was preceded by electron transfer (equations 11 and 12), because the proportions of isomers from the reaction of ArH + with N02 were quite different from those from the reactions of ArH with N02+ and with N204. Eberson and Radner set out to determine whether or not the conventional nitration of naphthalene and methylnaph-thalenes involved the electron-transfer step. In so doing they became, to our knowledge, the first to show that a neutral radical (N02) will react with an aromatic cation radical. 

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