Perylene cation radical, reaction with

Some years ago, following the discovery that Th + can be alkylated at sulfur by reaction with R2Hg, numbers of unsuccessful attempts were made to methylate the perylene cation radical with dimethylmercury (Me2Hg). The cation radical was reduced completely to perylene, but no evidence of meth-ylperylenes could be found (54). In particular, no trace of a perylene carboxylic acid was found when the aromatic hydrocarbon product was subjected to oxidation procedures that had been shown independently to convert meth-... 

Because the cyanide ion is so easily oxidized its apparent ability to react with aromatic cation radicals instead of being oxidized by them reflects the competition so often encountered in cation radical chemistry between nucleophilicity and oxidizability of a nucleophile. The subject has not been treated analytically yet. In the present context, the tri-p-anisylaminium ion is reduced by cyanide ion (Papouchado et al., 1969) in a very fast overall second-order reaction (Blount et al., 1970). The cation radicals of thianthrene, pheno-thiazine, and phenoxathiin are also reduced by cyanide ion (Shine et al., 1974). In none of these cases, incidentally, is the fate known of the cyano radical presumed to be formed. Perylene cation radical perchlorate, on the other hand, reacts with cyanide ion in acetonitrile solution to give low (13%) yields of both 1- and 3-cyano-perylene (Shine and Ristagno, 1972). 

Only a few reactions of acetate ion and other carboxylates with cation radicals arc known other than in anodic oxidations. Thus, perylene cation radical gave the 3-acetate and benzoate (Ristagno and Shine, 1971b). 

A particularly graphic example of electron-transfer photosensitization is the interaction of diphenyliodonium salts with perylene. Exposure of a dichloromethane solution of a mixture of these two compounds to UV light for 2 s results in the formation of the intensely blue-colored and relatively stable perylene eation-radical. The blue color remains in solution in air for a considerable time until it slowly fades. When this photolysis reaction is conducted in the presence of a cationically polymerizable monomer, the blue color of the perylene cation-radical is very transient. 

Nentral perylene reacts with N02, giving the cation-radical. Flowever, its formation is, in principle, a result of a-complex splitting. Another possible route of a-complex splitting consists of proton elimination and nitro perylene formation. As experiments show, the nitration of perylene is accompanied with collateral reactions of PerH, such as recombination and interaction with solvent molecules (Eberson and Radner 1985). This testifies to the release of cation-radical. 

Cation-radicals of naphthalene and its homologues, pyrene, or perylene react with NOj" ion in AN, giving electron-transfer products, that is, ArH and NOj. The latter radical is not very active in these reactions and nitration takes place only with extremely reactive compounds such as perylene (Eberson and Radner 1985, 1986). This mechanism is seemingly distinctive of compounds with E° less or equal to 1 V in AN (or in other solvents solvating NOj ions sparingly). 

Radical cations act both as electrophiles and one-electron oxidants toward nucleophiles (Eberson, 1975 Bard et al, 1976 Eberson et al., 1978a,b Evans and Blount, 1978) as shown in (6), and it is therefore important to find out which factors govern the competitition between these reaction modes. Evans and Blount (1978) measured rate constants and products for a number of [9,10-diphenylanthracene)+ /nucleophile reactions and found that iodide, rhodanide, bromide and cyanide undergo oxidation, whereas nucleophiles that are more difficult to oxidize form a C—Nu bond directly. Entry no. 13 of Table 15 shows non-bonded electron transfer to be feasible for these ions, and the reactions of [perylene]+ with iodide, rhodanide and bromide (entry no. 14) presumably can be classified in the same way. The reaction with chloride ion... 

Eberson and co-workers have recently discussed the probability that the interaction of ion-radicals with nucleophiles and electrophiles is subject to orbital symmetry constraints.31,32 This follows the observation that with perylene the cation-radical (18) the preferred course of reaction with halide ions is electron transfer rather than nucleophilic addition, whereas with the phenothiazine cation-radical (19) nucleophilic attack by Cl" and Br occurs. 

Perylene and tetracene both undergo photo-induced electron-transfer reactions with pyromellitic anhydride (Levin, 1976). If a mixture of perylene and tetracene is used, and the light absorbed by the perylene, the perylene radical cation will be formed which because of the relative oxidation potentials will react with tetracene to give the tetracene radical ion. Thus the photogenerated perylene radical cation has undergone a redox reaction with tetracene. In effect, the perylene has acted as a sensitiser for the production of the tetracene radical cation. This type of sensitisation has been used to effect a number of reactions. 

One of the important features of the coupling reaction that was brought out by Eberson and Radner (19, 20) is that it does not work for all ArH +. In particular, the perylene and pyrene cation radicals did not couple with N02. Reaction of the pyrene-dimer cation radical, (pyrene)2 +PF6 , with N02, for example, gave mainly tarry materials and less than 1% of 1-nitro-pyrene (19, 20). Eberson and Radner (19, 20) concluded that only cation... 

To our knowledge no reaction of iodide ion as a nucleophile with a cation radical is known. Iodide ion reduces cation radicals very well and is frequently used for the iodimetric assay of cation-radical salts. Since the reduction is reversible and some compounds can be oxidized to the cation radical stage by iodine, an excess of iodide is used. Some cation radicals are also reduced by other halide ions for example, that of 9,10-diphcnylanthracene is reduced by bromide ion (Sioda, 1968), that of perylene by bromide and chloride ions (Ristagno and Shine, 1971b), and thianthrene radical cation to some extent by chloride ion (Murata and Shine, 1969). These reductions, particularly those by iodide ion, reflect again the competition between nucleophilicity and oxidizability of a nucleophile in reactions with cation radicals. 

Fluoride ion reactions are somewhat puzzling. Oxidation of fluoride ion by a cation radical is out of the question and nucleophilic attack would appear to be certain. However, this reaction has failed completely with several cation radical perchlorates, such as those from perylene (Ristagno and Shine, 1971b), and phenothiazine (Shine et al., 1972). It appears that fluoride ion is too weak a nucleophile to participate in such substitution reactions. On the other hand, several cases of anodic fluorination are known oxidation of some aromatics, in solutions containing fluoride ion and at potentials lower than the oxidation potential of fluoride ion, has led to fluorination. This has occurred with naphthalene, which gave... 

When a molecule is photoexcited, the excited state is better electron donor as well as better electron acceptor than the ground state. In the presence of donor and acceptor which are not capable of conducting dark electron transfer reaction with each other or with sensitizer, the sensitizer may be recycled via radical cation or radical anion(Fig. 2). Detailed kinetic study on electron transfer sensitization of photooxidation of leuco crystal violet(LCV) in the presence of perylene(Pe), and 9-cyanoanthracene(CNA) or 1,4-dicyanobenzene(DCB) as sensitizer and acceptor, respectively, (3) provides the following information, i) Reaction between Pe and DCB is ca. 2.5 times faster than reaction between Pe and LCV. ii) The turnover number of Pe could be infinite in vacuo, iii) Oxygen could substitute the role of DCB. iv) The quantum efficiency of Pe-LCV-DCB ternary system is better than that by direct excitation of LCV-DCB system. v) When other solvents are used, solvents having high... 

Our experiences with nitrite-ion reactions show that both nitration and oxygen-atom transfer can occur. Thus, 6 " and 10 give 2-nitrodibenzodioxin (12) and 3-nitroperylene (10) respectively according to eq. 6. The cation radical of zinc tetra-phenylporphyrin is similarly nitrated at one of the pyrrolic carbon atoms (44). The perylene reaction is so facile that it... 

Not much is known about the last of our inorganic ion reactions, that of cyanide ion. A number of anodic cyanations and cyanation-methoxylation reactions are in the literature. These, anodic oxidations in solutions (methanol usually) of cyanide ion, are reactions of cyanide with cation radicals. Yet, the only successful "chemical reactions, we are aware of are with 10 " which gave small yields of 1- and 3-perylene nitrile (13), and with zinc octaethylporphyrin cation radical, which gives 68% of meso-cyanooctaethylporphyrln (49). 

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