Aminium radical ion

This aminium radical salt in aqueous solution in the form of solvated radical salt is very stable and will not polymerize acrylonitrile even with CeHsCOONa to form the corresponding benzoate. Therefore, we believe that in the nucleophilic displacement, there must be some intermediate step, such as intimate ion pair and cyclic transition state, which will then proceed the deprotonation to form the active aminium radical ion [14], as shown in Scheme 1. The presence of the above aminomethyl radical has also been verified [15] through ultraviolet (UV) analysis of this polymer formed such as PAN or PMMA with the characteristic band as the end group. 

Tertiary (and to a lesser extent, secondary) aromatic amines can also be prepared in moderate to high yields by amination with an N-chlorodialkylamine (or an N-chloroalkylamine) and a metallic-ion catalyst (e.g., Fe, Ti, Cu, Cr ) in the presence of sulfuric acid. The attacking species in this case is the aminium radical ion R2NH- formed by ... 

For a review of aminium radical ions, see Chow, YL. React. Intermed. (Plenum), 1980,1, 151. 

Fig. 12a—e. H CIDNP spectra of diethylvinylamine observed during the reaction of (a) anthraquinone with triethylamine, (b) benzoquinone with triethylamine in acetone-d6, (c) benzoquinone with triethylamine in acetonitrile-d3. Traces (d) and (e) show theoretical spectra calculated for the exclusive involvement of the aminoalkyl radical and of the aminium radical ion, respectively. The change from emission (trace a) to enhanced absorption (trace c) for the doublets near 6.0 ppm indicates an increasing involvement of the aminium radical ion [178]... 

Tor a review of aminium radical ions, see Chow, Y.L. React. Intermed. (Plenum) 1980, 1, 151. The reaction has been extended to the formation of primary aromatic amines, but the scope is narrow Citterio, A. Gentile, A. Minisci, R Navarrini, V. Serravalle, M. Ventura, S. J. Org. Chem. 1984, 49, 4479. 

The reaction is first carried out in acid solution. The photolysis of the TV-chloroammonium ions produces an aminium radical ion which, by abstraction of an H-atom from the methyl group, is converted into an alkyl radical. The latter initiates a chain reaction by abstracting a Cl-atom form a new TV-... 

Formation of an intimate ion pair of OH " and aminium radical cation was also proposed for the intermediate step before deprotonation. The presence of the above radical was verified through UV analysis of the polymer formed with the characteristic band on the end group. Through chromatographic analysis of the TBH-DMT reaction products, H2O was detected as the above mechanism proposes after deprotonation. 

The process for initiating radical formation in aromatic amine-vinyl monomer systems have been studied by Feng et al. [80-86] who proposed the formation of an aminium radical as the active state of an exciplex as intimate ion-pair and then a cyclic transition state which then would undergo a proton transfer process of deprotonation leading to the formation of active radical species for initiation as follows ... 

A more detailed evaluation of the diverse structures proposed for the secondary species goes beyond the scope of this review. We mwely emphasize that the ESR results provide detailed evidence for the nature of the radical center, but fail to elucidate the cationic site. The identity of this center is left to secondary considerations or speculation. We also note that any alternative structure has the virtue of not contradicting the ab irutio calculations the potential c ture of chloride ion has precedent in the nucleophilic substitution at a cyclopropane carbon (see Section 7). Another type of ring-opened structure has been postulated as an intermediate in the aminium radical cation catalyzed rearrangement of l-aryl-2-vinylcyclopropanes (see Section 5). 

Radical cations can be generated by many chemical oxidizing reagents, including Brpnsted and Lewis acids, the halogens, peroxide anions or radical anions, metal ions or oxides, nitrosonium and dioxygenyl ions, stable aminium radical cations, semiconductor surfaces, and suitable zeolites. In principle, it is possible to choose a reagent with a one-electron redox potential sufficient for oxidation-reduction, and a two-electron potential insufficient for oxidation-reduction of the radical ion. 

As with arene-amine radical ion pairs, the ion pairs formed between ketones and amines can also suffer a-deprotona-tion. When triplet benzophenone is intercepted by amino acids, the aminium cation radical can be detected at acidic pH, but only the radical formed by aminium deprotonation is detectable in base (178). In the interaction of thioxanthone with trialky lamines, the triplet quenching rate constant correlates with amine oxidation potential, implicating rate determining radical ion pair formation which can also be observed spectroscopically. That the efficiency of electron exchange controls the overall reaction efficiency is consistent with the absence of an appreciable isotope effect when t-butylamine is used as an electron donor (179). 

Flash photolysis and laser flash photolysis are probably the most versatile of the methods in the above list they have been particularly useful in identifying very short-lived intermediates such as radicals, radical cations and anions, triplet states, carbenium ions and carbanions. They provide a wealth of structural, kinetic and thermodynamic information, and a simplified generic experimental arrangement of a system suitable for studying very fast and ultrafast processes is shown in Fig. 3.8. Examples of applications include the keton-isation of acetophenone enol in aqueous buffer solutions [35], kinetic and thermodynamic characterisation of the aminium radical cation and aminyl radical derived from N-phenyl-glycine [36] and phenylureas [37], and the first direct observation of a radical cation derived from an enol ether [38],... 

A rich variety of chemical oxidizing reagents have been applied for the generation of radical cations. The principal reagent types include Bronsted and Lewis acids the halogens certain peroxide anions or radical anions numerous metal ions or oxides nitrosonium and dioxygenyl ions stable organic (aminium) radical cations ... 

The polarization observed in the photoreaction of anthraquinone is also consistent with the concept of two consecutive intermediates [178]. Anthraquinone is a poorer oxidizing agent than benzoquinone so that the corresponding radical ion pair is less stable. Consequently, the aminium radical cation decays faster and does not contribute appreciably to the vinylamine polarization. 

Neutral aminyl radicals bearing electron-withdrawing tV-substituents (for example, amidyl radicals), or aminium radicals (protonated aminyl radicals) and metal ion complexed aminyl radicals are more reactive due to the lower nonbonding electron density on nitrogen, and consequently the diminished repulsive interaction with the it electrons of the alkene4,6. 

One-electron transfer from the substrate amino group to flavin (FI) results in the formation of the aminium radical and the flavin radical anion (FC) (Scheme 15). Deprotonation of the aminium radical to yield an a-aminoalkyl radical followed by a second electron transfer to the flavin radical anion will result in the formation of the reduced flavin and iminium ion. Alternatively the iminium ion can be formed by path d in Scheme 15 this involves formation of a covalent adduct which can... 

The enzyme cytochrome P450 metabolizes tertiary amines in the liver by a one-electron transfer mechanism. An electron is transferred from N to a heme group featuring an Fe=0 bond to give an aminium radical cation and the radical anion [Fe]-0-. An a-hydrogen atom is then abstracted by the oxygen-based radical to give an iminium ion. Flydrolysis of the iminium ion affords a secondary amine and an aldehyde, both of which are further oxidized into water-soluble compounds and then excreted. The oxidation of tertiary amines to secondary amines can also be executed in the laboratory. 

Aminium radicals were not considered until now as intermediates in photosta-bilizing mechanisms of HAS. These unstable ion-radicals were reported to be formed transiently by photolysis of HAS [172],... 

Amination refers to the reaction of the aminium radical (NH ) and its dialkyl derivatives (R2NH +) with organic substrates, particularly with olefins and aromatics. The aminium radical itself can be generated by the reduction of hydroxylamine O-sulfonic acid with ferrous ion (147) (Minisci and Galli, 1965). Dialkylaminium radicals are generated in several ways, the most common being the reduction of N-chlorodialkylamines by ferrous ion in acidic solution (148) and... 

Sosnovsky and Rawlinson (1972), and Minisci (1975), while work with nitrosamines has been carried out and reviewed by Chow (1973). The reduction of an amine oxide by ferrous ion also gives an aminium radical (Lindsay Smith et al., 1973). Danen and Rickard... 

The mechanism in Scheme 8 was proposed for the oxidation reaction. In the first step, the Cu(II) salt, which is formed in the autooxidation of cuprous chloride, forms a complex with the amine. This is followed by a rate-determining electron transfer from the amine to the Cu(II) species giving Cu(I) and an aminium radical. The subsequent steps were considered to be fast. The authors accounted for the secondary hydrogen-deuterium kinetic isotope effect by suggesting that there was hyperconjugative electron release to the aminium ion nitrogen that forms in the slow step of the reaction. 

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