Radical anion of acridine

Nitrogen heteroaromatics are expected to be useful probases. The cathodic reduction of phenazine, (31), resembles closely that of (29a) [70,71], and the kinetic basicity of (31) is comparable to that of (29a) [54]. However, application of (31) as a PB in electrosynthesis has not been reported, and there is only a single report concerning the use of the radical anion of acridine, (32), as an EGB [72]. 

Radical anions of acridine (95) dimerize in DMF to give the corresponding dimer dianion [270] (Table 21). The reduction remained a 1-F process upon addition of 10% (v.v) water but led to a fivefold increase in the value of On a voltammetric time scale, the dimerization appeared irreversible in the absence as well as in the presence of water. On a preparative scale, the dimer 9,9, 10,10 -tetrahydro9,9 -biacridyl could be isolated... 

Absorbed dose 0.15 Mrad at 77°K. A = radical anion of acridine C = radical cation of acridine R = neutral radical [175],... 

Fig. 29. G value for the formation of radical anion of acridine at 77°K in PMMA containing various amounts of acridine (calculated from the optical density at 635 nm). Absorbed dose 0.1 Mrad at 77°K [175].

Fig. 34. Stepwise decay of radical anion of acridine in PMMA containing 0.26 mole dm-3 acridine. Absorbed dose 0.2 Mrad at 77°K (optical density measured at 635 nm) [259].

Among condensed heterocyclic compounds formation of radical ions have been proved for the following compounds radical anions of acridine [117], phthalazine [126], phenazine [70, 126], 1,4,5,8-tetraazanaphthalene [131], 9,10-diazaphenanthrene [129], 2,2 -biiso-benzimidazolidine [129], and phenothiazone [108] radical cations for... 

The ESR hyperfine coupling constants have been established experimentally (67MI20402) for the pyridinyl radical (134 R = H) and deuterated analogues, produced by y irradiation of a solid solution of pyridine in ethanol at 77 K, but the signs of the couplings are not known experimentally and are made solely on the basis of Huckel MO calculations. INDO MO calculations on this radical, together with the radical anions of quinoline, isoquinoline and acridine h ve also been carried out (740MR(6)5). 

Reductive dimerization of benzene [246], cyano biphenyl ether [247], pyridine [248], and acridine [249] derivatives has also been investigated. Radical anions of diesters of pyridine and benzene undergo rapid reversible dimerization (A dim = 10 -10 M" s" ) [250]. 

The importance of radical ions and electron-transfer reactions has been pointed out in the preceding sections (see also p. 128). Thus, in linear hydrazide chemiluminescence (p. 103) or acridine aldehyde or ketone chemiluminescence, the excitation steps consist in an electron transfer from a donor of appropriate reduction potential to an acceptor in such a way that the electron first occupies the lowest antibonding orbital, as in the reaction of 9-anthranoyl peroxide 96 with naphthalene radical anion 97 142> ... 

The ESR spectra of phenalenone, acridine, and benzoquinone anil radical anions were recorded by W. C. Danen, E. T. Strom, and F. A. Neugebauer. 

Crooks, R. M. and Bard, A. J. (1988b) Electrochemistry in near-critical and supercritical fluids. Part V. The dimerization of quinoline and acridine radical anions in ammonia from 70°C to 150°C. J. Electroanal. Chem. 240, 253-279. 

The presence of MEF, MEP and Metal-Enhanced superoxide anion radical generation in the same system seems surprising at first, as these processes are effectively competitive and ultimately provide a route for deactivation of electronic excited states. As recently shown by the authors, simultaneous photophysical mechanisms can be present within the same system when enhanced absorption effects of the fluorophore near to silver are present (i.e. an enhanced excitation rate). In this case, enhanced absorption of Acridine near-to the plasmon resonant particles facilitates MEF, MEP, ME Oa and also Metal-Enhanced superoxide generation simultaneously within the same system. Aaidine showed an enhanced absorption spectra near-to silver, similar to other probes reported by the authors, in essence acridine absorbs more light. ... 

There is one report concerning the use of electrogenerated acridine radical anion as EGB, namely to induce the elimination reaction depicted later in Scheme 17 leading to the substituted cyclobutene [44]. The workup, however, was found to be easier using superoxide anion as EGB see Sec. III.B.l. 

To the more usual homolytic fragmentation of aryl halides (from the excited state or from the radical anion, the well known SrnI reaction, for a recent example see the arylation of aromatics), the heterolytic version of the reaction which produces phenyl cations has more recently joined. A theroretic study on the photodissociation of fluorinated iodobenzenes has been published. The perfluoroallgrlation of various alkenes has been obtained by irradiation in the presence of iodoperfluorobutane. The formation of phenyl cations is exemplified in many arylation reactions and, in the case of o-chlorostannane, also a benzyne has been reported. In the field of polymer chemistry, iodonium salts are model cationic photoinitiators. In particular the truxene-acridine/diphenyl iodonium salt/9-vinylcarbazole combination is able to promote the ringopening polymerization of an epoxide, whereas the truxene AD/allq l halide/amine system is very efficient in initiating the radical photopolymerization of an acrylate. ... 

In complex cases, the prefixes amino- and imino- may be changed to ammonio- and iminio- and are followed by the name of the molecule representing the most complex group attached to this nitrogen atom and are preceded by the names of the other radicals attached to this nitrogen. Finally the name of the anion is added separately. For example, the name might be 1-trimethylammonio-acridine chloride or 1-acridinyltrimethylammonium chloride. 

The first reduction wave for phenanthridine jV-oxide in dimethyl-formamide (at 25°) appears at — 1.774 (vs. s.c.e.) in good agreement with the HMO energy of the lowest vacant orbital277 a mechanism for the reduction has been proposed.278 No esr signal could be detected during controlled-potential electrolysis at the appropriate potential, perhaps because of the relative instability of the anion radical. This behavior, which is paralleled by isoquinoline, contrasts sharply with that of the oxides of other polynuclear N-heteroaromatic systems (e.g., quinoline and acridine).277... 

The electrochemical behavior of the A-D compounds (selected structures are shown in Fig. 16) agrees well with that expected on the basis of the electrochemical properties of both the donor and the acceptor moieties [134-138]. That they can be reversibly reduced and oxidized to the corresponding radical cation and anion has been ascertained by cyclic voltammetry. The standard reduction potentials, are close to the values found for the parent aromatic hydrocarbons or acridine [124]. In a similar way, the standard oxidation potentials, °, are congruent with those found for the corresponding amines [148]. The electrochemical reaction of A-D compounds can be formulated as follows ... 

Acridine and phenothiazine cocrystallized to give two kinds of hydrogen-bonded CT crystals. Both crystals showed some photoreactivity and appear to have given many photoproducts (Scheme 18) [44]. Although this crystalline complex is complicated in terms of stoichiometry, crystal structure, and photoreaction, a transient study by femtosecond diffuse reflectance spectroscopy was carried out, as had been done for durene-pyromellitic dianhydride cocrystal [45]. For the yellow cocrystal, a transient absorption spectrum with maxima around 600 and 520 nm was obtained, which decayed biexponentially with lifetimes of 2 and 50 ps. The two absorption maxima were ascribed to the acridine anion radical and the phenothiazine cation radical, respectively. 

Under circumstances where the sensitizer is efficiently reduced by the donor in the excited state, then one can obtain photoreduction of MV2+ via a reductive cycle. Proflavine and other acridine dyes sensitized reduction of MV2+ as well as Zn-Porphyrin sensitized reduction under high donor concentrations have been shown111,319 to follow such a mechanism. In both cases, the photogenerated sensitizer anion-radicals being good reductants themselves, also can play the role of the acceptor (relay) molecules. With efficient Pt-PVA catalysts, it has been shown118,333 to be the case for proflavine and Ru(bipy)3. 

Organic metals have also been used as the electrode material for the adsorption of peroxidase.The electrochemical properties of these organic metals, which are complexes of iV-methylphenazine (NMP ) or N-methyl-acridine (NMA ) with the anion radical of tetracyano-n-quinodimethane (TCNQ") with composition NMP TCNQ", NMP "(TCNQ")2, or NMA TCNQ , have been reported.Hydrogen peroxide electroreduction on the organic metals takes place in the presence of peroxidase for Er < 0.2 V (Figure 28). In the case of the enzyme adsorbed on NMP TCNQ", the reaction starts at Er> OS V. In the opinion of the authors, these data point to the presence of a direct electron exchange between the electrode and peroxidase. There are, however, certain apprehensions that, because of partial solubility, the organic metals may act as mediators. 

Figure 6.13 illustrates two pathways that had been proposed for the transfer hydrogenation reaction of acridan (54) and a-methylstyrene (55) to give acridine (56) and cumene (57). The top pathway proceeds by transfer of a hydride ion from 54 to 55 to give an ion pair intermediate, which subsequently transfers a proton to the anion to complete the reaction. The bottom pathway is a radical mechanism that involves a sequence of two hydrogen atom transfers. Previous reports suggested that the reaction of acridan with a-methylstyrene and the reaction of DDQ with 1,4-cyclohexadiene most likely involved the radical pathway but that some other transfer hydrogenation reactions followed the ionic pathway. 

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