Oxidation of diphenylamine

The powder turns dark blue if it contains a large quantity of solvent and if it is exposed to the action of hot air, e.g. on drying at a temperature of 50-60°C. The investigations of Desmaroux [68), Marqueyrol and Muraour [69] and of Mar-queyrol and Loriette [70] showed that this is due to the oxidation of diphenylamine produced by peroxides formed from residual ether and atmospheric oxygen. 

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. 

A study of [Rh(phen)3]3+ confirmed that emission comes from a (n-n ) state.819 No emission was observed in fluid solution, but a long-lived excited state occurs in DMF at room temperature, as 290 nm irradiation of [Rh(phen)3]3+ causes the characteristic 780 nm phosphorescence of [Cr(CN)6]3 (equation 146). The Sterm-Volmer constant of 3.0 x 103 M I implies a lower limit for the excited state lifetime of ca. 0.30 ms. Sensitization of biacetyl, and the oxidation of diphenylamine (in acetonitrile) and of 1,3,5-trimethoxybenzene are also observed for [Rh(phen)3]i+, implying that the 3(7t-7t ) state of [Rh(phen)3]3+ is a powerful oxidant. A potential of 2.00 V is calculated for the [Rh(phcn),]3+/[Rh(phen),]3 + couple,819 making the excited state of [Rh(bipy)3]3+ a better oxidant than the Ru , Cr111 or Os11 analogs. 

When visual indicators are used, the rate of attainment of equilibrium depends on the type of reaction leading to color development, which may be slow. For simple electron exchange reactions like that of ferroin, the rate of indicator response is usually rapid. If, however, the indicator undergoes a more deep-seated structural change, one can anticipate kinetic complications. The oxidation of diphenylamine, for example, is induced (Section lS-8) by the iron(II)-dichromate reaction. 

In the foregoing discussion the indicator has tacitly been assumed to come rapidly to equilibrium at each point of the titration curve. That this is an over-simplihcation is evident from a number of experimental observations. Kolthoflf and Sarver found that the oxidation of diphenylamine with dichromate is induced by the Fe(II)-dichromate reaction. The direct oxidation is so slow that the indicator blank is best determined by comparison of the visual with the potentiometric end point. With ferroin. Smith and Brandt and Stockdale foimd that the reverse titration, dichromate with iron, gave satisfactory results at sufficiently high acidities, whereas the direct titration failed because the indicator could not be oxidized. Here the oxidation seems to be slow and the reduction rapid because of the irreversible nature of the oxidant and the reversible nature of the reductant. 

Electro-oxidation of diphenylamine systems has received extensive attention. Recent interest has been associated with the preparation of electronically conductive polymers, such as polyaniline. An important role of p-aminodiphenylamine in the anodic oxidation of aniline is well documented and therefore fundamental electrochemical properties... 

Conflicting accounts of the dye-sensitized photo-oxidation of diphenylamine in alcohols have been published, with one group of workers152 reporting diphenylnitroxide as the product, and another group158 repeating their claim (see Vol. 6, p. 545) that iV-phenyl-p-benzoquinonimine is formed. The photo-oxidation of 2,4,6-triphenylpyridine TV-phenylimine may involve ozone production.154... 

The oxidation of diphenylamine by [FeCCN) ] " in alkaline media gives N-phenyl-p-benzoquinoneimine(PBQ) and [Fe(CN)6] with the stoicheiometric ratio being [oxidant]/[PBQ] = The reaction is first order in both reactants,... 

Kinetic spectrophotometric methods have also been used. The catalytic effect of manganese(II) on the oxidation of diphenylamine-4-azo-benzen-4 -sul-fonic acid potassium salt with potassium periodate in the presence of 1,10-phenanthroline in weak media has been reported, with an LOD of 0.017ng mH A sensitive flow injection procedure is based on the catalytic effect of manganese on the oxidation of 2-2 -azinobis(3-thylbenzothiazoline-6-sulfonic acid) with periodate (415 nm). 

The fact that the azotoxide radical, produced by the oxidation of diphenylamine, is itself an antioxidant was noted by Thomas, who compared the inhibition of the oxidation of white oil by additives of small amounts of diphenylamine and diphenylazotoxide [82]. 

The chlorine formed by (2) can also be detected through the selective oxidation of diphenylamine described on page 177. 

The well-known diphenylamine color reaction of nitric acid depends on the oxidation of diphenylamine (I) through colorless N,N -diphenylbenzidine (II) to the blue quinoid imonium ion (III) ... 

Coloured oxidation products, a) Dissolve a few small crystals of diphenylamine in 1 ml. of cone. H2SO4. Add 2 drops of cone. HNO3 to about 10 ml. of water, shake, and add i drop of this diluted HNO3 to the diphenylamine solution an intense purple-blue coloration is produced. Monomethylaniline merely turns a dirty brown when treated in this way. 

The first detailed investigation of the reaction kinetics was reported in 1984 (68). The reaction of bis(pentachlorophenyl) oxalate [1173-75-7] (PCPO) and hydrogen peroxide cataly2ed by sodium saUcylate in chlorobenzene produced chemiluminescence from diphenylamine (DPA) as a simple time—intensity profile from which a chemiluminescence decay rate constant could be determined. These studies demonstrated a first-order dependence for both PCPO and hydrogen peroxide and a zero-order dependence on the fluorescer in accord with an earher study (9). Furthermore, the chemiluminescence quantum efficiencies Qc) are dependent on the ease of oxidation of the fluorescer, an unstable, short-hved intermediate (r = 0.5 /is) serves as the chemical activator, and such a short-hved species "is not consistent with attempts to identify a relatively stable dioxetane as the intermediate" (68). 

Mention should be made of one of the earliest internal indicators. This is a 1 per cent solution of diphenylamine in concentrated sulphuric acid, and was introduced for the titration of iron(II) with potassium dichromate solution. An intense blue-violet coloration is produced at the end point. The addition of phosphoric(V) acid is desirable, for it lowers the formal potential of the Fe(III)-Fe(II) system so that the equivalence point potential coincides more nearly with that of the indicator. The action of diphenylamine (I) as an indicator depends upon its oxidation first into colourless diphenylbenzidine (II), which is the real indicator and is reversibly further oxidised to diphenylbenzidine violet (III). Diphenylbenzidine violet undergoes further oxidation if it is allowed to stand with excess of dichromate solution this further oxidation is irreversible, and red or yellow products of unknown composition are produced. 

DeAtley WW (1970) Spectrophotometric determination of diphenylamine, 2-nitrodipheny-lamine, and 4-nitrodipheylamine by oxidation with ferric ion. Anal Chem 42(6) 662-664... 

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. 

The intermediate formation of the nitroxyl radical was detected in the oxidation of 2-propanol retarded by diphenylamine chain termination occurs by cyclic mechanisms involving both... 

A second important group includes the diphenylamine indicators. In the presence of a strong oxidizing agent, diphenylamine is irreversibly converted to diphenylbenzidine. This latter compound undergoes a reversible redox reaction accompanied by a colour change,... 

The oxidative coupling/cyclization process occurs via stoichiometric carbo-palladation using a Pd(II) species, typically Pd(OAc)2. In an early example, submission of diphenylamines 3 to the palladium(II)-promoted oxidative intramolecular cyclization conditions yielded carbazoles 4 [15-... 

Akermark et al. reported the palladium(II)-mediated intramolecular oxidative cyclization of diphenylamines 567 to carbazoles 568 (355). Many substituents are tolerated in this oxidative cyclization, which represents the best procedure for the cyclization of the diphenylamines to carbazole derivatives. However, stoichiometric amounts of palladium(II) acetate are required for the cyclization of diphenylamines containing electron-releasing or moderately electron-attracting substituents. For the cyclization of diphenylamines containing electron-attracting substituents an over-stoichiometric amount of palladium(II) acetate is required. Moreover, the cyclization is catalyzed by TFA or methanesulfonic acid (355). We demonstrated that this reaction becomes catalytic with palladium through a reoxidation of palladium(O) to palladium(II) using cupric acetate (10,544—547). Since then, several alternative palladium-catalyzed carbazole constructions have been reported (548-556) (Scheme 5.23). 

The oxidative closure of diphenylamines has been achieved with iodine at 350°C and with platinum at 450-540 C. ° Carbon-carbon bonding via displacement of the halogen of a 2-chlorophenyl-3 -hydroxyphenylamine clearly must involve intramolecular nucleophilic displacement para to phe-noxide. ... 

Treatment of diphenylamine with base and traces of oxygen in DMSO solution yielded a significant ESR signal that we have identified as I. The same radical is formed spontaneously from the mono-anil of p-benzoquinone in basic DMSO and by the oxidation of 4-hydroxydi-... 

Oxidation of the anion from diphenylamine apparently involves attack of oxygen at carbon rather than nitrogen. ... 

The oxidation of AT-substituted 5//-dibenz[6,/] azepines with MCPBA is complex and depends upon the nature of the N-substituent. AT-Acyl derivatives do not form the N-oxide but suffer epoxidation of the 10,11-bond. AT-Aryl derivatives undergo hydroxylation of the phenyl ring, whereas N-alkyl congeners, with the exception of the AT-methyl compound, yield mixtures of diphenylamines and acridones. The N-oxide is obtained from the A/-methyl derivative along with ring-opened and ring-contracted products (81CPB1221). 

Investigations have shown that the basic properties of diphenylamine are so weak that it cannot hydrolyse nitrocellulose, but they are sufficiently strong to neutralize any acid product arising either from the decomposition of impurities in the nitrocellulose, from the oxidation of residual solvent or even from decomposition of the nitrocellulose itself. It was also demonstrated that the basic properties of diphenylamine may have a deleterious effect on the powder if the diphenylamine content exceeds 5%. The best stabilizing results are achieved by using 1.0-2.5% diphenylamine. 

---