Triphenylamine oxidation

Coloured oxidation products, (a) Dissolve a few small crystals of triphenylamine in i ml. of cone. H2SO4 (cf. footnote, p. 376). Add 2 drops of cone. HNO3 to about 10 ml. of water, mix, and add i drop of this diluted HNO3 to the triphenylamine solution an intense greenish-blue coloration is produced. Dimethylaniline when treated in this way turns a deep dichromate colour. 

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... 

The electrochemical Wacker-type oxidation of terminal olefins (111) by using palladium chloride or palladium acetate in the presence of a suitable oxidant leading to 2-alkanones (112) has been intensively studied. As recyclable double-mediatory systems (Scheme 43), quinone, ferric chloride, copper acetate, and triphenylamine have been used as co-oxidizing agents for regeneration of the Pd(II) catalyst [151]. The palladium-catalyzed anodic oxidation of... 

The polymers can be oxidized by differential pulse polarography. Their oxidation is metal-centered and leads to Ru(III) compounds. The potential is located aroimd -1-1.26 V (SCE). It can be stated that the polymers which contain the triphenylamine structure imits in the main chain show, as expected, an additional peak caused by the amine nitrogen. Substitution at the triphenylamine by electron-donating substituents lowers these potentials to 1.05 V (25), whereas acceptor substituents cause an increase of the oxidation potential (23). 

Anodic oxidation of triphenylamine gives the radical-cation which is rapidly converted to the dehydrodimer, tetraphenylbenzidine. A para-substituent prevents this dimerization and gives radical-cations very stable in acetonitrile solution against nucleophiles [155], This class of compound was first prepared as the per-... 

When cyclohexene is used as substrate, cyclohexene oxide is formed with selectivities exceeding 95% at conversions up to 89% [89]. The activity increases with increasing Mo content and is poisoned by tributyl amine, but not by triphenylamine, which is too bulky to enter the zeolite pores. These results... 

Yamamoto also explored triphenylamine core dendrimers of the form Corei7-Rpti2-Periph15.125 In this system, the redox process studied was the oxidation of this core moiety. They showed that as the generation of the dendrimer increased from 1 to 4, the shape of the CV broadened, indicating slowing electron transfer kinetics. 

Oxidative cleavage by means of electrochemically generated cation-radicals is also possible thus benzyl ethers may be cleaved and carboxylates decarboxylated using cation-radicals of brominated triphenylamines in acetonitrile containing a weak base.34 35 Such as indirect reaction makes it... 

The conversion of substituted diphenylamines and triphenylamines to carbazoles at platinum anodes in CH3CN-Et4NC104 takes place if the intermediate cation-radical is fairly stable. Thus the anodic oxidation of (V-ethylbis(p-fert-butylphenyl)amine (87) gave 3,6-di-ferf-butyl-Af-ethyl-carbazole (88) in 15% yield152 [Eq. (72)]. 

It has been suggested in the literature that the a-amino radical is the species that initiates polymerization [210], This view is supported by our observation that, in spite of the relatively high quenching rate constant of Eosin triplet by triphenylamine (Table 5), the system Eosin-triphenylamine does not sensitize the photopolymerization of multifunctional acrylates. Thus, it is necessary that the amine contains a hydrogen at the a-carbon to be released as a proton after oxidation of the amine by the dye triplet. This deprotonation prevents the back electron transfer and forms a carbon radical that is sufficiently long-lived to be captured by the monomer. 

Fleischmann et al s 34 report cyclic voltammetry data for the oxidation of a series of aromatic hydrocarbons in a molten salt electrolyte, AlCl3-NaCl-KCl at 150°. Electrooxidation in this medium occurs at unusually low oxidation potentials. Tris-(p-substituted phenyl)amines, with the exception of tri (p-nitrophenyl) amine, yield very stable radical cations by all electrochemical criteria 380>S42 Mono- and bis-p-substituted triphenylamines, however, dimerize with rate constants ranging from 101 to 10s M 1 sec 1 to benzidines 176 (Eq. (237)), which subsequently are oxidized to the radical cations 177, whose ESR-spectra are observed. Dimerization is fastest with the p-N02 andp-CN-derivative, in accordance with HMO calculations, which predict the highest spin sensity in the p-position of these compounds 542 ... 

SbClj has been claimed to act as an electron-transfer oxidant toward a number of reagents, such as N,N,N, N -tetramethylphenylenediamine, triphenylamine, 2,4,6-tri-t-butylphenolate ion, ferrocene, and N-vinylcarbazole. Among these, triphenylamine is the most difficult to oxidize, and was therefore chosen as a model compound in entry no. 18. By matching the lowest possible experimental rate constant, 103 s , with rate constants calculated as a function of E° for the SbClj/SbCl - couple, the latter was estimated to be 0.54 V. This is an entirely reasonable value (see Cowell et al., 1970). 

A number of organic solutes undergo reaction with AICI3. For example, aromatic amines dissolve in the room-temperature molten electrolyte butylpyridinium chloride. Triphenylamine (TPA) shows two stages of oxidation upon polarographic examina-... 

The reaction of n radical cations with n nucleophiles usually leads to C-C bond formation, a reaction that can be very fast (cf. pericyclic reactions also), as in the oxidative dimerization of triphenylamine k = 1-10 x 10 M s ) [293], Hence, such a reaction mechanism can even operate in anodic oxidations (4-methoxybiphenyl [294], tetrahydrocarbazole [295], 4,4 -dimethoxystilbene [296] and 9-methoxyanthracene) [297], where the radical cation concentration is very high. 

Usually, aromatic amines are very easy to oxidize. Unsubstituted, A-alkyl-, and N,N-dialkylanilines show anodic potentials in the range of 0.4 to 1.0 V (vs. NHE). Diphenylamines cover a broader spectrum of potentials depending on their substitution pattern. Triphenylamines have oxidation potentials between 0.7 and 2.0 V (vs. NHE). For aromatic amines, a large number of potentials has been tabulated [33], The anodic oxida-... 

Triphenylamines are coupled to the tetraphenylbenzidines, which may be reversibly further oxidized to their dications (Table 5, number 1). The rates of the coupling reaction have been measured, and a fairly complete picture of the oxidation pathways has emerged [68]. /7flra-Substituted triphenylamines cyclize to some extent to carbazoles [69]. 

Amine radical-cations have been generated by the treatment of para-substituted anilines with ceric ion (Stone and Waters, 1962 Fox and Waters, 1964). When the para position is free, the initial radical-cation can react further for example, the oxidation of triphenylamine with lead tetra-acetate in the presence of boron trifluoride (Allara ei al., 1965) or with iodine (Stamires and Turkevich, 1963) gives the radical cation Ph3N+ , and, when excess of triphenylamine is used, the former oxidant leads to the radical-cation of A(, .A/, W, A -tetraphenylbenzidine. The only radical observed by the oxidation of dimethylanihne either electrochemically (Mzoguchi and Adams, 1962) or with lead tetraacetate and boron trifluoride (Allara et al., 1965) is the radical-cation of iV, .A, .A7, iV -tetramethylbenzidine. The relatively stable (hindered) anilino radical (40) has been generated from the corresponding aniline by flash photolysis audits e.s.r. spectrum has been measured in n-hexane (Land and Porter, 1961). The electronic spectrum of this radical is very similar to that of the unsubstituted anilino radical, detected during flash photolysis of aniline, but this radical is so short-lived that it has not yet been detected by e.s.r. 

The one-electron reduction of triphenylamine by sodium or potassium gives the biphenyl radical-anion (Iwaisumi and Isobe, 1965). In contrast, triphenylphosphine and potassium give a radical-anion which is thought to be Ph2P—K the same species is formed from diphenyl-phosphine with an excess of potassium (Britt and Kaiser, 1965). More recently, Cowley and Hnoosh (1966) have found that the reduction of triphenylphosphine oxide with sodium in dimethoxyethane gives the biphenyl radical-anion, whereas reduction with potassium gives, in tetrahydrofuran, PhsPO" and, in dimethoxyethane, a spectrum very similar to that reported by Britt and Kaiser but which is attributed to Ph2P(0)K-. 

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