The photochemical reaction of aromatic amines with carbon tetrachloride

This paper is dedicated to Professor Camille Sandorfjr on the occasion of his 65th birthdayBOGUMIL ZELENT and GILLES DUROCHER. Can. J. Chem. 63, 1654 (1985.The mechanism of the photodecomposition of N-ethylcarbazole (NEC) in the presence of carbon tetrachloride has been discussed on the basis of the photoproducts identified. The photodissociation of the N-ethyl bond and the electron transfer in the transiently formed ex-CT complex, '(NEC"..-CCI.,'-)*, have been proposed as the primary photochemical processes involved irr the singlet excited NEC molecule. The latter, treated as the main process, leads to the radical cation of NEC, chloride ion, and trichloromethyl radical in the solvent cage, [NEC"CI-CCI,]. The other reactions in the system studied are analysed following the decomposition of NEC" in the presence of C1-and CCI,, which can occur by the N-ethyl group and (or) by the aromatic ring. The formation of intermediate products such as in the solvent cage gives rise to secondary photochemical reactions in the system studied. The polarity and chemical activity of the reaction media used strongly influence the nature of the secondary photochemical transformations both in and outside the solvent cage. The formation mechanism of the photochemical reaction products in CCI, when ammonia was used, after and during irradiation, has been explained mainly by the transformations of the radical a, and cation a~. as well as by the carbazyl radical P, which is also formed in the reaction medium. On the other hand, reaction of the cation y: explains the formation of the photoproducts in the irradiated solution of NEC with CClj in ethanol. These photochemical results have been compared to the photochemical reactions involved in the carbazole-CC14 system. BOGUMIL ZELENT et GILLES DUROCHER. Can. J. Chem. 63, 1654 (1985).Le mCcanisme de la photodCcomposition du Cthyl-N-carbazole (NEC) en prksence de tktrachlorure de carbone (CCI,) est analysC suite ['identification des photoproduits obtenus. La photodissociation du lien N-Cthyl ainsi que le transfert Clectronique dans le complexe excitC de transfer de charge '(NEC''...CCI,'-)* peuvent Ctre la cause de l'acte photochimique primaire suite a I'excitation du NEC dans son Ctat premier singulet. Le phototransfert Clectronique conduit I'apparition du radical cation du NEC, a I'anion chlorure et au radical trichloromCthyl dans la cage du solvant, [NECt'CI-CCI,]. La dCcomposition du radical cation en prksence de C 1 et de CCI, s'effectue par I'attaque du groupe N-Cthyl ou par le noyau aromatique. Les produits intermkdiaires suivants: dans la cage du solvant donnent lieu a ]'ensemble des rCactions photochimiques secondaires. La polarit6 ainsi que I'activitC chimique du milieu rkactionnel influencent fortement la nature des transformations photochimiques secondaires dans la cage du solvant et en dehors de celle-ci. Le mecanisme de formation des produits photochimiques dans le CCI, lorsque I'ammoniaque est ajoutC au cours et aprks I'irradiation s'explique principalement par la transformat...

Section: Resultsmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

One-electron photooxidation of N-ethylcarbazole in the presence of carbon tetrachloride. Products and mechanism of the photochemical reaction

Zelent¹,

Durocher²

1985

“…Among various halocarbons, carbon tetrachlor-Studies of the mechanism of fluorescence quenchide is most frequently used as a fluorescence ing by halocarbons focused the attention of researchers upon the possibilities of photochemical um or as the active component of the medium for molecule. This has been supported by studies on photochemical reaction of many potential electron the photophysical properties of the carbazoledonors (8)(9)(10)(11)(12)(13)(14)(15)(16). Such studies not only strongly CCl, system in various media (I), as well as by the supported the electron transfer mechanism used to explain the fluorescence quenching but also depicted new possibilities of the application of an electron acceptor like CCl, in photochemical synthesis.…”

Section: Introductionmentioning

confidence: 80%

“…The presence of ammonia in excess, acting as a good scavenger of HC1 in the reaction medium, favours the course of reactions [9] to [12]. Decomposition of (carboimino-N-carbazy1)carbazoles to carbazole and cyano derivatives of carbazole in reactions [ I l l and [12] requires a certain activation energy.…”

Section: Use Of Nh After Irradiationmentioning

confidence: 99%

One-electron photooxidation of carbazole in the presence of carbon tetrachloride. Part II. Carbon tetrachloride as a reaction medium. Use of ammonia after irradiation and during irradiation

Zelent¹,

Durocher²

1982

BOGUMIL ZELENT and GILLES DUROCHER. Can. J. Chem. 60,2442Chem. 60, (1982.In part I of this series of papers we proposed the mechanism of electron transfer as the primary photochemical reaction in the carbazole -carbon tetrachloride system along with a secondary photochemical reaction initiated by transformations of the radical cation of carbazole in the solvent cage resulting in intermediates:CCI, H [ &I , ]@f@l, andIn this paper we discuss the influence of ammonia, used afier and during irradiation, on the mechanism of secondary transformation and the formation of thermodynamically stable products in the system studied. Such compounds as N-cyanocarbazole, I-cyanocarbazole, and 3-cyanocarbazole have been formed as the main products during neutralization of the photolyte solution by ammonia gas. The mechanism of formation of these compounds has been explained by the chemical reaction of ammonia with cations a and yi. If ammonia is present in the solution of carbazole in CCI, during irradiation, such products as N ,N1-dicarbazyl and N-cyanocarbazole are mainly formed along with 3-(N-carbazyl)carbazole, 3,9-di-(N-carbazyl)carbazole, and N-cyano-3-(N-carbazyI)carbazole. In such a case, reactions of radicals P are the determining factors in the secondary photochemical transformations. Radicals P are formed by the reaction involving ammonia with radical cations of carbazole. All the results in this paper have been discussed taking under consideration the influence of the reaction media o n the mechanism of photochemical transformation of carbazole.BOGUMIL ZELENT et GILLES DUROCHER. Can. J. Chem. 60, 2442Chem. 60, (1982.Dans la premiere partie de cette sCrie d'articles nous avons suggerk que le mdcanisme photochimique primaire lors de la reaction du carbazole et du tetrachlorure de carbone en etait un de transfert Clectronique. La reaction photochimique secondaire consiste e n la transformation du radical cation du carbazole dans la cage du solvant pour donner les intermediaires suivants:Dans cet article, nous discuterons de l'influence de l'ammoniac utilise apres et avant l'irradiation, sur le mCcanisme secondaire d e transformation et de formation de photoproduits thermodynamiquement stables. Lorsque I'ammoniac est ajoute apres l'irradiation, le cyano-N carbazole, le cyano-l carbazole et le cyano-3 carbazole ont ttC surtout obtenus. Ce resultat s'explique par la rdaction d e I'ammoniac avec les cations a et y,. Si au contraire, l'ammoniac est present dans la solution du carbazole dans le CC1, au cours d e l'irradiation, les produits suivants sont obtenus avec un bon rendement: dicarbazyl-N,N' et cyano-N carbazole. Les produits suivants sont Bgalement obtenus: (carbazyl-N)-3 carbazole, di-(carbazyl-N)-3.9 carbazole et cyano-N(carbazy1-N)-3 carbazole.Les radicaux p sont alors impliquks dans la transformation photochimique. Ces radicaux P sont produits suite a la rdaction de l'ammoniac avec les radicaux cations du carbazole. Tous les resultats sont discut6s en tenant compte de I'influence du milieu riactionnel sur le...

“…Halocarbons, and CCl, in particular, have been shown to be efficient fluorescence quenchers for a number of molecules (18)(19)(20)(21). It has also been shown that polar solvents increase this quenching (22,23).…”

Section: Introductionmentioning

confidence: 99%

Quenching of the singlet and triplet state of benzene in condensed phase

Khwaja¹,

Semeluk²,

Unger³

1984

Quenching of the fluorescence of benzene by halocarbons in methanol, ethanol, acetonitrile, and cyclohexane has been investigated. It proceeds via a reversible exciplex intermediate formed between excited singlet benzene and ground state halocarbon. Quenching is controlled by the polarity of the medium. Excited singlet benzene interacts with acetonitrile solvent and a longer wavelength emission due to this complex is observed.The effect of CCl4, CH3CN, CHCl3, and CH3CCl3 on the triplet and singlet excited states of benzene in a methylcyclohexane–isopentane mixture at 77 K has been examined. Carbon tetrachloride and acetonitrile are far more effective quenchers than either CHCl3 or CH3CCl3. In the case of the latter pair enhanced intersystem crossover competes with complex formation.