Tetraphenylhydrazine

Most observations of SCRP have been from triplet preeursors, but Fiikuju et al [61] have observed smglet-bom SCRP upon photolysis of tetraphenylliydrazine in sodium dodeeyl sulfate (SDS) mieelles. The tetraphenylhydrazine (12) eleaves to fomi two diphenylamino (DPA) radieals, as shown below. 

Figure Bl.16.18. TREPR spectra observed after laser excitation of tetraphenylhydrazine in an SDS micelle at room temperature. Reprinted from [61].

High values of the inhibition coefficient (/= 12-28) were detected for the first time in the oxidation of cyclohexanol [1] and butanol [2] inhibited by 1-naphthylamine. For the oxidation of decane under the same conditions, /= 2.5. In the case of oxidation of the decane-cyclohexanol mixtures, the coefficient / increases with an increase in the cyclohexanol concentration from 2.5 (in pure decane) to 28 (in pure alcohol). When the oxidation of cyclohexanol was carried out in the presence of tetraphenylhydrazine, the diphenylaminyl radicals produced from tetraphenylhydrazine were found to be reduced to diphenylamine [3]. This conclusion has been confirmed later in another study [4]. Diphenylamine was formed only in the presence of the initiator, regardless of whether the process was conducted under an oxygen atmosphere or under an inert atmosphere. In the former case, the aminyl radical was reduced by the hydroperoxyl radical derived from the alcohol (see Chapter 6), and in the latter case, it was reduced by the hydroxyalkyl radical. 

Experiments—Dissolve about 0-5 g. of tetraphenylhydrazine in 5 c.c. of xylene and warm the solution slowly over a small flame. The initially colourless solution becomes intensely olive green, even before the boiling point of the solvent is reached. The colour is that of the free radicle which, at this temperature, very rapidly under-1 Cf. F. Sachs, Ber., 1901, 34, 497. 

Experiment.—Pour concentrated sulphuric acid on to a few centigrammes of tetraphenylhydrazine. A beautiful red colour at first appears it changes in a short time to intense blue-violet. 

When the dye is formed from tetraphenylhydrazine, diphenyl-hydroxylamine (pp. 182, 341) is first produced by hydrolysis at the N—N-linkage. 

Tetraphenylhydrazine (5 g.) is dissolved in 40 c.c. of toluene in a small round-bottomed flask fitted with a two-holed cork. A delivery tube, which is connected to the apparatus just described and reaches to the bottom of the flask, passes through one hole, a short glass tube through the other. With the second wash-bottle disconnected from the rubber tube, and the latter closed by means of the clip, the dropping in of sulphuric acid is begun, and at the same... 

A close analogy to the carbon radicles is provided by certain nitrogen compounds, which are likewise free unsaturated complexes partaking of the character of atoms and having an abnormal valency. With nitrogen, as with carbon, the existence of radicles also depends on the presence of aromatic rings. Tetraphenylhydrazine corresponds to hexa-phenylethane. 

The reversible dissociation of colorless tetraphenylhydrazine into the green diphenylaminyl (15) at 100°C was discovered by Wieland in 1911 (equation 7), and extended the free radical concept to nitrogen. These radicals are trapped by nitric oxide to give diphenylnitrosoamine (16), and the rate of this reaction was used to show the rate of dissociation of the hydrazine. ... 

Ph2N PhsN - NPh2 diphenylnitrogen from tetraphenylhydrazine In a strict sense also ... 

Much research has been devoted to finding the mechanism of the changes which diphenylamine undergoes in powder. Marqueyrol and Loriette [70] report that under the action of oxidizing agents, particularly of peroxide formed from ether, diphenylamine undergoes the following reactions to produce tetraphenylhydrazine (I) and diphenylphenazine (II) ... 

Diphenylamine is only slowly converted even at higher temperatures (50% water 50% t-butanol, O.IM KOH, 50 °C) and there it yields thermal decomposition products, that possibly originate from tetraphenylhydrazine . ... 

Tetraphenylhydrazine is a while solid, soluble in chloroform, acetone, benzene, or toluene, and upon standing is changed into triphenylaminc plus azobenzene. In solution, tetraphenylhydrazine dissociates into nitrogen diphenyl. (Ct,Hs) N-. free radical, which in toluene at 90cC reads with nitric oxide, NO, Tetraphenylhydrazine is formed by oxidation of diphenylamine,. by lead dioxide. 

Several specific oxidative transformations of nitrogen compounds can be carried out in the presence of copper salts. Oxidation of o-phenylenediamine with molecular oxygen in the presence of a twofold excess of CuCl in pyridine results in the formation of cis,cw-mucononitrile in high yield (equation 286).618 619 The bis- i-oxo tetranuclear complex Cu4Cl402(py)4 was found to be the active species in this transformation.618 A similar procedure can be used for the selective oxidative coupling of diphenylamine to tetraphenylhydrazine by CuCl/py/02 or Cu4Cl402py4 (equation 287).619... 

F. A. Neugebauer, M. Bock, S. Kuhn-hauser, H. Kurreck, Darstellung, ESR-und ENDOR-Untersuchung von Radi-calkationen des Tetraphenylhydrazins, des 5,6-Dihydro-5,6-diphenylbenzo[c]-cinnolins und des Benzo[c]benzo[3, 4]cinnolino[l,2-a]cinnolines, Chem. Ber. 1986, 119, 980-990. 

Many free radical-generating compounds have been disclosed as synergists which may be used in place of peroxides to enhance the selfextinguishing action of bromine compounds. Examples of some of these materials are the disulfides, sulfenamides, a,a -diphenyl-a-methoxybi-benzyl, N-nitroso-N-methylaniline, tetraethyllead, pentaphenylphosphine, 1,2-diphenyltetramethylethane, tetraphenylhydrazine, and heavy metal salts or chelates (7, 9, 40, 41, 42, 55, 59 71, 90, 132). 

Kavun and Buchachenko (247) have found that the "primary" amino radicals derived from thioamines in the presence of hydroperoxide are very stable and are not readily converted into "secondary" nitroxide radicals. Kommandeur and Wiersma (107) studied the photodecomposition of tetraphenylhydrazine in rigid solution at 77°K, and the observed ESR spectrum was assigned to the dimer of the diphenyl amino radical (248). Shida et al. (249) have also studied the photodimer of tetraphenylhydrazine and the photochromic dimer of triphenylimidazolyl at low temperature by optical and ESR techniques. These authors noted that photolysis of these compounds induces the homolysis while y-irradiation leads to heterolytic dissociation. Blinder et al. (250) reported the ESR spectrum of the monomer tetraphenylpyrryl radical in... 

The one-electron oxidation of a secondary amine results in the formation of a secondary aminium ion which on deprotonation gives an aminyl radical (Scheme 1). The nature of the final products derived from these intermediates dqiends very much on the structure of the substrate and the reaction conditions. If the amine has a hydrogen atom on the a-carbon atom the major products usually result from deprotonation at this a-position. With aromatic secondary amines, products can result from coupling of the delocalized radicals at a ring carbon atom. The formal dimerization of aminyl radicals shown in Scheme 21 is therefore not often a useful method of preparation of hydrazines. Nickel peroxide has been used to oxidize diphenylamine to tetraphenylhydrazine in moderate yield, and other secondary arylamines also give... 

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