Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Phenylenediamines radical cations

Experimentally, the molecular geometry has been determined by X-ray analysis for several larger radicals. These data indicate, in agreement with the theory, that bond alternation characteristic in many reduced and oxidized closed-shell forms is diminished in radical ions. Precise crystallographic data are available for 4,4 -A/s(dimethylamino)diphenylamine radical cation (87, 88), N,N -diphenyl-p-phenylenediamine radical cation (89), and Wiirster s blue (90). [Pg.347]

Allyl (27, 60, 119-125) and benzyl (26, 27, 60, 121, 125-133) radicals have been studied intensively. Other theoretical studies have concerned pentadienyl (60,124), triphenylmethyl-type radicals (27), odd polyenes and odd a,w-diphenylpolyenes (60), radicals of the benzyl and phenalenyl types (60), cyclohexadienyl and a-hydronaphthyl (134), radical ions of nonalternant hydrocarbons (11, 135), radical anions derived from nitroso- and nitrobenzene, benzonitrile, and four polycyanobenzenes (10), anilino and phenoxyl radicals (130), tetramethyl-p-phenylenediamine radical cation (56), tetracyanoquinodi-methane radical anion (62), perfluoro-2,l,3-benzoselenadiazole radical anion (136), 0-protonated neutral aromatic ketyl radicals (137), benzene cation (138), benzene anion (139-141), paracyclophane radical anion (141), sulfur-containing conjugated radicals (142), nitrogen-containing violenes (143), and p-semi-quinones (17, 144, 145). Some representative results are presented in Figure 12. [Pg.359]

N,N-Dimethyl-p-phenylenediamine Radical Cation (DMPD ) DMPD Assay... [Pg.288]

DMPD (N,N-dimethyl-p-phenylenediamine) radical cation decolorization assay... [Pg.105]

Fig. 18. Chemiluminescence spectra of the 4,4 -dimethylbiphenyl radical anion/tetrame-thyl-p-phenylenediamine radical cation reaction in 1,2-dimethoxyethane a) without b) with an external magnetic field of ca. 1400 gauss (From Zachariasse [29]). Fig. 18. Chemiluminescence spectra of the 4,4 -dimethylbiphenyl radical anion/tetrame-thyl-p-phenylenediamine radical cation reaction in 1,2-dimethoxyethane a) without b) with an external magnetic field of ca. 1400 gauss (From Zachariasse [29]).
The -phenylenediamines are special and are used in many appHcations where the other isomers are ineffective. They are unique because they are more readily oxidi2ed than the meta or ortho isomers, as seen by the ioni2ation potentials Hsted in Table 2. The enhanced reactivity of -phenylenediamine is due to the high degree of resonance stabili2ation of its radical cation. [Pg.254]

Kemp and coworkers employed the pulse radiolysis technique to study the radiolysis of liquid dimethyl sulfoxide (DMSO) with several amines as solutes [triphenylamine, and N, A, A, N -tetramethyl-p-phenylenediamine (TMPD)]. The radiolysis led to the formation of transient, intense absorptions closely resembling those of the corresponding amine radical cations. Pulse radiolysis studies determine only the product Ge, where G is the radiolytic yield and e is the molar absorption. Michaelis and coworkers measured e for TMPD as 1.19 X 10 m s and from this a G value of 1.7 is obtained for TMPD in DMSO. The insensitivity of the yield to the addition of electron scavenger (N2O) and excited triplet state scavenger (naphthalene) proved that this absorption spectrum belonged to the cation. [Pg.895]

Exceeding the limitation of molecular dynamics, the steric requirement of trimethylsilyl groups can cause drastic changes both in structure and of molecular properties of organosilicon compounds. For illustration, the so-called "Wurster s-Blue11 radical ions are selected On one-electron oxidation of tetramethyl-p-phenylenediamine, its dark-blue radical cation, detected as early as 1879 [11a], is gene-... [Pg.357]

The electrogenerated radical anions of aromatic hydrocarbons, e.g. DPA, rubrene, fluorene, can also act as reductants towards electro-chemically obtained radical cations which are derivatives of other aromatic compounds such as N,N-dimethyl-/>-phenylenediamine (Wurster s red) 150> (see Section VIII. B.). When a mixture of DPA and a halide such as 99 (DPACI2) or 100 is electrolysed, a bright chemiluminescence is observed the quantum yields are about two orders of magnitude higher than that of the DPA radical anion-radical cation reaction 153>. [Pg.122]

Another assay that is very similar to the ABTS assay is the AGV-dimethyl-p-phenylenediamine (DMPD assay). In the presence of a suitable oxidant solution at an acidic pH, DMPD is converted to a stable and colored DMPD radical cation (DMPD +). Antioxidants capable of transferring a hydrogen atom to the radical cause the decol-orization of the solution, which is spectrophotometrically measured at 505 nm. The reaction is stable, and the endpoint is taken to be the measure of antioxidant efficiency. Antioxidant ability is expressed as Trolox equivalents using a calibration curve plotted with different amounts of Trolox (Fogliano and others 1999). This method is used to measure hydrophilic compounds. The presence of organic acids, especially citric acid, in some extracts may interfere with the DMPD assay, and so this assay should be used with caution in those extracts rich in organic acids (Gil and others 2000). [Pg.288]

Triphenylamine (TPA), AWW W -tetramethyl-p-phenylenediamine (TMPD) and dimethylaniline (DMA) have been popular substrates for reaction under pulse radiolysis conditions. One of the earlier reports dealt with the formation of the radical cation of TMPD by reaction (k = 3 x 108 M 1 s 1) with the peroxy radical derived from oxidation of methylene chloride (CHCI2O2) by pulse radiolysis26. DMA is also oxidized to its radical cation by the same reagent (k = 2.5 x 107 M 1s 1). Since then it has been... [Pg.826]

Anodic conversion of aromatics proceeds in most cases by le-transfer to the anode to form a radical cation (34) (Scheme 9). Oxidation is facilitated by extension of the 7T-system ( 1/2 vs. Ag/Ag+ benzene 2.08 V, pyrene 0.86 V) and by electron donating substituents ( 1/2 vs. Ag/Ag+p-phenylenediamine —0.15 V). Oxidation potentials of polycyclic aromatics and substituted benzenes are collected in Ref [140-142]. [Pg.149]

One-electron oxidation of aniline derivatives gives a radical-cation in which the unpaired electron is distributed over both the nitrogen atom and the aromatic system. The further reactions of these intermediates more resemble those of aromatic compounds than of aliphatic amines. Some of the radical-cations are very stable in solution Wurster s blue, prepared by oxidation of tetramethyl-1,4-pheny ene-diamine [152], and Wurster s red from N,N-dimethyI-l,4-phenylenediamine [153] have been known since 1879. They were recognised as radical-cations by Mi-chaelis [154]. [Pg.218]

The first organic radical cations, derived from p-phenylenediamine, date back to Baeyer s Strassburg laboratory in 1875. Wurster recognized these (Wurster s)... [Pg.207]

The photooxidation of p-phenylenediamine to the Wurster s Blue radical cation apparently proceeds by photoionization of the excited triplet state of the neutral molecule,219 and it has been suggested that the delayed fluorescence of perylene may be partly due to photoionization of its triplet state and slow subsequent recombination of... [Pg.68]

DPPH, l,l-Diphenyl-2-picrazyl ABTS+, 2,2 -azinobis(3-ethylbenzthiazoline-6-sulfonic acid) radical cation FRAP, ferric-reducing activity of plasma Fem-TPTZ, ferric tripyridyltriazine DMPD, N, IV-dimethyl-o-phenylenediamine ESR, electron spin resonance. [Pg.232]

As for halogens as oxidizing reagents, bromine has proved more useful than its homologs chlorine and iodine. It was employed as early as 1879 on di- and tetra-methyl-p-phenylenediamine [27-29] and early in this century, Wieland used it to generate the aminium salts of triarylamines and tetraarylhydrazines [30, 31]. Since bromine adds readily to unsaturated as well as to some strained ring compounds, it is not expected to be very useful in the context of the radical cations discussed here. [Pg.134]

The starting point is the Wurster s Blue radical cation, discovered in 1879 and thoroughly investigated since then The twofold N pyramidal IVWW. /V -tetraalkyl-p-phenylenediamine precursors are completely flattened on two-electron oxidation as proven by crystal structure analyses of the resulting redox salts (Scheme 8a). [Pg.203]

Using the experimental setup and conditions mentioned earlier, Jean-maire and Van Duyne (77) studied one-electron oxidation of N,N,N, N -tetramethyl-/7-phenylenediamine (TMPD) to its radical cation (TMPD +, Wurster s Blue). [Pg.174]

Radical disproportionation induced by electron transfer. Several interesting and interrelated phenomena occur when N J I, N -tetramethyl-1,4-phenylenediamine (TMPD) is added to the solution of [CpM(CO)3l2 prior to the laser flash. As expected from the electrode potential of TMPD /TMPD, 0.16 V vs SSCE in acetonitrile, the first event is the rapid growth of the intense absorption band of the amine radical cation centered at 613 nm (e = 1.2 X 10 L mol cm" ). This absorption then fades fairly rapidly. The fading was quite unexpected, since TMPD " normally persists indefinitely. This phenomenon is illustrated in Figure 2. Indeed, when independently-prepared TMPD was injected into the cuvette after the laser flash its blue color persisted indefinitely. [Pg.210]

It was discovered several decades ago that spontaneous thermal electron transfer from encapsulated aromatic organics to the zeolite framework is possible. Although the exact location of the electron on the framework was not determined, dehydration of the zeolite, the zeolite topology and the nature of the co-cations in the zeolite were found to be important in generating the radical species. NH4-Y zeolite rather than Na-Y was necessary for formation of radical cations of 1,1-diphenylethylene, triphenylamine, quinoline, perylene, aniline and p-phenylenediamine [126]. Recent studies have shown that stable, radical cations of a,(U-diphenylpolyenes can be formed thermally on activated Na ZSM-5 [127]... [Pg.2810]

Optical absorption spectroscopy of organic radical cations was pioneered by Hoijtink and coworkers and others before the advent of PE spectroscopy, but it was limited for a long time to aromatic amines, polycyclic aromatic hydrocarbons and similar compounds whose radical cations could be generated under stable conditions by chemical oxidation. It was observed that many colourless neutral compounds give rise to intensely coloured radical cations which indicates that excited states of these reactive species lie generally at much lower energy than those of the neutral parent molecules (the most famous example is perhaps Wurster s blue, the radical cation of the colourless tetramethyl-p-phenylenediamine). [Pg.228]

Another interesting species is WWAf W -tetramethyl-p-phenylenediamine, the parent neutral of the well-known radical cation, Wurster blue. Its enthalpy of formation as a solid75 is 39.6 3.9 kJ mol 1. Equations 16 and 17 might be expected to be thermoneutral. The calculated enthalpy of reaction of the former is 5.9 kJmol-1 and that of the latter is —7.1 kJ mol 1, adequate indication that the enthalpies of formation are essentially accurate. [Pg.275]

The electrochemical properties of phenylenediamines, in particular of para-phcnylcnc-diamine (83), have been studied intensively. In aqueous media, the oxidation potentials of these compounds depend upon the pH value, since the amino group can be protonated. In the pH range of 2-6, the radical cation 831 can be generated anodically as demonstrated... [Pg.907]

A few promised chapters on the acidity of anilines, on polyanilines and on radical cations of triarylamine and phenylenediamine were not delivered. We hope to include these chapters in a future supplementary volume. [Pg.1155]


See other pages where Phenylenediamines radical cations is mentioned: [Pg.131]    [Pg.131]    [Pg.254]    [Pg.895]    [Pg.228]    [Pg.358]    [Pg.11]    [Pg.93]    [Pg.155]    [Pg.145]    [Pg.207]    [Pg.869]    [Pg.6]    [Pg.6]    [Pg.155]    [Pg.452]    [Pg.912]    [Pg.1050]    [Pg.896]    [Pg.968]   
See also in sourсe #XX -- [ Pg.560 ]




SEARCH



1,2-Phenylenediamine

Phenylenediamines

© 2024 chempedia.info