Pyridine cation radical, reactions

In regard to the reactions of cation radicals with stable radicals, such as l,l-diphenyl-2-picrylhydrazyl, and with well-known spin traps, virtually nothing can be found in the literature. The pyridine cation radical has been reported to add to the spin trap phenyl-N-tert-butyl nitrone (37). 

Goodin, 1970). Thus, there is no point in searching for the esr spectrum of the pyridine cation radical. Probably the same situation prevails in reactions of other amines with TCNE. For example, a variety of arylamines react with TCNE and form, finally, tricyano-vinyl derivatives (Foster, 1974). The reaction is thought to involve complex formation first (Isaacs, 1966). The TCNE - is produced over a period of minutes, while the other anticipated radical, presumed to be an aminium ion, is not observed. Its absence is attributed to dimerization and proton loss, although the anticipated products (hydrazobenzene and its isomers) are not found. In these reactions, therefore, there can be little doubt that the TCNE" - arises from reactions of TCNE with hydroxide ion and/or cyanide ion (formed in the tricyanovinylation reaction). Thus, in these cases the formation of an anion radical is not linked to electron transfer from an organic donor (Isaacs, 1966). 

Pyridine cation radical was identified as a reaction intermediate by spin trapping with phenyl-N-t-butyl nitrone (142). The very stable... 

Tire self-chemical ionization reaction of CS2 under chemical ionization conditions (approx. 1 Torr) generated 83, which sulfurized pyridine (97MI1) and nitriles (97JPC6970) to give the corresponding cation radicals 61 and 62, respectively. Ab initio calculations on 83 at the G2 (MP2, 8VP) level revealed that the ylide radical cation form 63 is more stable than the dithiiranethione radical cation form (64) by 42 kJ/mol (97JPC6970). 

Table 4 Second-order reactions of aromatic cation radicals with nitrogen dioxide, pyridine or 2,6-lutidine."...

The sterically hindered base 2,6-bis(tert-butyl)pyridine does not inhibit cyclization triaryl-amine retards this reaction photosensibilized one-electron oxidation of a diene leads to the same products, which are formed in the presence of ammoniumyl salt. As shown, in majority of cases, only the cation-radical chain mechanism of the diene-diene cyclization is feasible (Bauld et al. 1987). Meanwhile, cyclodimerizations of 2,4-dimethylpenta-l,3-diene (Gassman and Singleton 1984) and l,4-dimethylcyclohexa-l,3- or -1,4-diene (Davies et al. 1985) proceed through both mechanisms. 

Here, eB is the molar absorption coefficient of substance B, and CA and DA are the concentration and the diffusion coefficient, respectively, of substance A. The A(t)-t relation changes when reaction (9.2) occurs. By simulating the expected A(t)-t relation and comparing with the experimental results, the rate constant k can be obtained. This method is useful for studying the reaction of radical ions in non-aqueous solutions. For example, the reactions of the cationic radical (DPA +) of 9,10-diphenylanthracene (DPA) with such bases as water and pyridine were... 

The most common reactions involving nucleophiles and porphyrin systems take place on the metalloporphyrin 77-cation radical (i.e. the one-electron oxidized species) rather than on the metalloporphyrin itself. One-electron oxidation can be accomplished electrochemi-cally (Section 3.07.2.4.6) or by using oxidants such as iodine, bromine, ammoniumyl salts, etc. Once formed, the 77-cation radicals (61) react with a variety of nucleophiles such as nitrite, pyridine, imidazole, cyanide, triphenylphosphine, thiocyanate, acetate, trifluoroace-tate and azide, to give the correspondingly substituted porphyrins (62) after simple acid catalyzed demetallation (79JA5953). The species produced by two-electron oxidations of metalloporphyrins (77-dications) are also potent electrophiles and react with nucleophiles to yield similar products. 

Pyridylarenes undergo Cu(II)-catalysed diverse oxidative C-H functionalization reactions. The tolerance of alkene, alkoxy, and aldehyde functionality is a synthetically useful feature of this reaction. A radical-cation pathway (Scheme 4) has been postulated to explain the data from mechanistic studies. A single electron transfer (SET) from the aryl ring to the coordinated Cu(II) leading to the cation-radical intermediate is the rate-limiting step. The lack of reactivity of biphenyl led to the suggestion that the coordination of Cu(II) to the pyridine is necessary for the SET process. The observed ortho selectivity is explained by an intramolecular anion transfer from a nitrogen-bound Cu(I) complex.53... 

Radical 80 has been prepared as its perchlorate salt by anodic oxidation in ethyl acetate in the presence of hthium perchlorate. The reactivity toward nucleophiles of material so prepared was investigated nitrite and nitrate ions give 2-nitrodibenzo[l,4]dioxin although the mechanisms of the reactions are not clear. Pyridine gives 7V-(2-dibenzo[l,4]dioxinyl)pyridinium ion (84). Other nucleophiles acted as electron donors and largely reduced 80 back to the parent heterocycle they included amines, cyanide ion and water. In an earlier study, the reaction of 80 with water had been examined and the ultimate formation of catechol via dibenzo[l,4]dioxin-2,3-dione was inferred. The cation-radical (80) has been found to accelerate the anisylation of thianthrene cation-radical (Section lII,C,4,b) it has been found to participate in an electrochemiluminescence system with benzo-phenone involving phosphorescence of the latter in a fluid system, and it has been used in a study of relative diffusion coefficients of aromatic cations which shows that it is justified to equate voltammetric potentials for these species with formal thermodynamic redox potentials. The dibenzo[l,4]dioxin semiquinone 85 has been found to result from the alkaline autoxidation of catechol the same species may well be in-... 

Cyclic voltammograms of 48 recorded in ACN solutions containing as much as fivefold excess of pyridine are almost identical to those obtained without this base89. In both cases the product of the anodic reaction is the dimer 49. Identical electrochemical responses in the presence and in the absence of pyridine imply that there are no detectable interactions between the cation radical 48 and the pyridine molecules. However, diverse transformation of the decay profiles of 48 depending on the concentration of pyridine was observed using an electron transfer stopped-flow technique. The last observation was ascribed to the interaction between 48+ and pyridine, in which the proton is extracted by the molecule of the base89. One can therefore assume that this is an example of the process for which the voltammetric measurements at conventional scan rates cannot give full information about the pathway of the electrochemical reaction. 

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