Diphenylamine, photolysis

Laser Flash Photolysis at 351 nm of tert-Butyl Peroxide/Benzene Solutions Containing MDI-PUE and Model Compounds. Photolysis of tert-butyl peroxide (TBP) results in a highly efficient production of tert-butoxy radicals. It has recently been shown (15) that tert-butoxy radicals generated by the laser flash photolysis of TBP can rapidly extract hydrogen atoms from appropriate substrates such as aniline and diphenylamine (Scheme III). 

In another study, the irradiation (X = 290-310 nm) of hexachlorobenzene in an aqueous solution gave only pentachlorobenzene and possibly pentachlorophenol as the transformation products. The photolysis rate increased with the addition of naturally occurring substances (tryptophan and pond proteins) and abiotic sensitizers (diphenylamine and skatole) (Hirsch and Hutzinger, 1989). 

Tanaka et al. (1981a) studied the photolysis of monuron in dilute aqueous solutions in order to fully characterize a substituted diphenylamine that was observed in an earlier investigation (Tanaka et al., 1977). They identified this compound as an isomeric mixture containing 92% 2-chloro-4, 5-bis(TV, TV -dimethylureido)biphenyl and 8% 5-chloro-2,4 -bis(TV, TV -dimethylureido)-biphenyl. 

The rate constant of this reaction was measured by flash photolysis with tetraphenyl-hydrazine as a source of diphenylaminyl radicals [64]. Peroxyl radicals were generated through the photodecay of bis(l,l-dimethylethyl) peroxide followed by the rapid reaction of formed alkoxyl radicals with cyclohexane used as a solvent the reaction conditions were chosen in such a way that [R02 ]o > [Ph2N ]0. Under these conditions, aminyl radicals were destroyed only in the reaction with peroxyl radicals and, hence, the concentration of peroxyl radicals during the measurement of the kinetics of Ph2N consumption varied insignificantly. The rate constant of the recombination of peroxyl and diphenylamine radicals was found to be equal to 6 x 108 L mol 1 s 1 (cyclohexane, 283-303 K). 

Historically, the first color-forming reaction to be discovered which involves electron transfer is probably the photoinitiated reaction of diphenylamine with carbon tetrabromide, which forms blue colors [42]. In fact, the major path for color formation is due to radical reactions, initiated by photolysis of C—Br bonds to produce Br3C and bromine atoms. An alternative mechanistic path, possible when the light is absorbed by the diphenylamine, would involve electron transfer. MacLachlan has shown that such processes do occur durin> photolysis of aminotriarylmethanes in the presence of electron acceptors such as CBr4 and CC14 [43]. Other electron deficient species (quinones, nitroaromatics) were also demonstrated to be effective. 

When primary and secondary co-arylalkylamines are excited, exciplex fluorescence is not observed, but fluorescence quenching does take place (Shizuka et al., 1979). Presumably chemical reaction competes effectively with exciplex formation. However, by means of picosecond laser flash photolysis, the time-resolved absorption spectra of the species produced on reaction of pyrene with diphenylamine have been obtained (Okada et al., 1980b). It was shown that the reaction leads to neutral radicals via an exciplex. Although the formation of neutral radicals in such systems had been previously identified (Okada et al, 1976a) the role of exciplexes had been purely speculative. 

The photolysis of diphenylamine in EPA at 90 °K results in fluorescence and photoionization the resulting amine cation has a lifetime of 4-16 /isec . The emission observed in solid matrices at 77 °K was thought to be due to the ion-l-electron recombination reaction ... 

Spectral analysis of the emission, however, showed, that it was actually delayed phosphorescence, i.e. (PhjNH) produced in the ion-electron recombination must be in a triplet state °. esr studies on transients produced in the photolysis of di-diphenylamine in alcohols at low temperatures also confirmed the existence of (PhjNH) and demonstrated an overall 2-photon absorption mechanism involving a triplet-triplet transition The quantum yield of phosphorescence is 0.05. ... 

Carbazoles can be prepared by photocyclisation of diphenylamines and this has now been applied to the synthesis of ellipticine alkaloid precursors. The ultra-violet light irradiation of N-tosyl amines (261) in ethanol is also said to give the corresponding carbazoles (262). Photolysis of the antiinflammatory drug diclofenac (263) in water or methanol has been... 

The photocycllsation of the pyridyl amine (220) to yield carboline (221) was described some years ago. It has now been found that the reglochemistry of this reaction can be changed so that C-N bond formation occurs instead of C-C bond formation if a chlorine atom is present to direct the orientation of the cycllsation. Thus irradiation of (222) yields the heterocycle (223). The photolysis of diphenylamines has been performed in the present of bromoform, chloroform and tribromomethylbenzene and is found to yield acridines (224). ... 

Thermolysis or photolysis of 2-azidobiphenyl produces a nitrene, as does deoxygenation of 2-nitrobi-phenyl with triethyl phosphite. The nitrene cyclizes immediately to give carbazole. Carbazoles can also be made by cyclodehydrogenation of diphenylamines. 

Type Ic cyclization can be applied to iV,iV-diarylamines to obtain carbazoles. Photolysis of diphenylamine leads to an electrocychzation which is followed by oxidation. Under anaerobic... 

If aryl azides are irradiated in acidic medium in the presence of arenes, derivatives of diphenylamine are formed." For the diphenylnitrenium ion, G-complexes with benzene have been detected by laser flash photolysis. In reactions with alkenes, nitrenium ions react more rapidly with electron-deficient olefins. Rate constants for the reaction of diphenylnitrenium with electron-rich olefins such as cyclohexanone trimethylsilyl enol ether are of the order of 1.9 x 10 M" s". In the reaction of 2-fluorenylni-trenium with 2 -deoxyguanosine, reaction at C8 of the guanine base takes place. ... 

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