One-electron photooxidation of carbazole in the presence of carbon tetrachloride. Part I. Carbon tetrachloride and ethanol used as reaction media

Abstract

This paper is dedicated to Professor Carnille Sandorfy on the occasion of his 60rh birthday BOGUMIL ZELENT and GILLES DUROCHER. Can. J. Chem. 60,945 (1982). The photochemical reaction products of carbazole with carbon tetrachloride in ethanol have been isolated and identified along with photoproducts in the irradiated solution of carbazole in pure CCI, using water and ethanol added after the irradiation. This allowed us to discuss the complex mechanism of secondary photochemical changes in the carbazole-CCI, system. We propose :hat the electron transfer from carbazole to CCI, molecule in the excited CT complex, '(C" +..CCI,")*, is the primary photochemical reaction followed by an heterolytic dissociation of a C-CI bond which gives rise to the primary photoproducts in the solvent cage [c+'cI-~cI,]. Secondary photochemical reactions initiate transformation of the radical cation of carbazole in the solvent cage giving rise to the following intermediate species:The probability of formation and further transformations of these transient products: a , P, and y,, depends strongly on the nature of the reaction media. Thermodynamically stable products are formed depending on the reaction media; (carboethoxy)carbazoles, (carbo-N-carbazyl)carbazoles, and carbazole -carboxylic acids can serve as a proof for the formation of the above listed intermediates. All the results reported on the secondary photochemical reactions strongly support the electron-transfer primary mechanism used to explain the fluorescence quenching of carbazole by CCI,.These results also explain the changes observed in the fluorescence spectrum of carbazole when the ethanol solution of carbazole in the presence of CCI, is irradiated.BOGUMIL ZELENT et GILLES DUROCHER. Can. J. Chem. 60,945 (1982). Nous avons isole et identifie les produits de la reaction photochimique entre le carbazole et le titrachlorure de carbone d'abord dans I'ethanol comme solvant mais aussi dans le CCI, pur utilise comme solvant pendant I'irradiation alors que I'eau et I'ethanol etaient ajoutees au CCI, apres I'irradiation. Ceci nous a permis de discuter du mecanisme complexe des reactions photochimiques secondaires dans le systeme carbazole-CCI,. Nous proposons que I'ttape photochimique primaire soit le transfert electronique du carbazole au CCI, par I'intermkdiaire d'un complexe de transfert de charge excite '(C"+CCI,")* suivi par une dissociation htterolytique d'un lien C-CI donnant lien a l'apparition des photoproduits primaires [c+'cI-~cI,] dans la cage du solvant. Par reactions photochimiques secondaires, les especes intermediaires suivantes seraient formees dans la cage du solvant:La probabilite de formation et tgalement de transformation de ces especes'transitoires a , P et yi depend beaucoup de la nature des milieux reactionnels. La nature des photoproduits thermodynamiquement stables formis est en fonction de la nature du milieu reactionnel. Les molecules de (carboethoxy)carbazoles, de (carbo-N-carbazyl)carbazoles et d'acides carbazole -carboxylique formees demontrent bien...

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

“…the following compounds: 3,9-di-(N-carbazy1)car-carbazole-CC1, system according to the following: bazole (24), N-cyano-3-(N-carbazy1)carbazole (26), and 3-(N-carbazy1)carbazole (27) in addition ['I C + hv + 'C* to products 1, 3, 22,28, and 29 (second column in [2] 'c* + cCI, -1(C~+.CCI,6-)*s,l, Table 1). [3] l(c6+ ~~.cC1,6-)*,,,, -[ c + ' c1-CCI,],,~, All the isolated and identified products, using ammonia after and during irradiation, support the carbazole radical cation transformation mechanism that we proposed in part I (15).…”

“…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.…”

“…Nevertheless, such interactions appear in the first electronic excited singlet state of the carbazole fact that fluorescence quenching of carbazole by CCl, is accompanied by a photochemical reaction (14). The proposed mechanism of the photochemical transformations in the carbazole-CC1, system has been discussed in detail in part I of this series of papers (15). This paper is a continuation of the discussion of the photochemical reactions involved in the carbazole-CC1, system, considering this time the influence of ammonia on the formation of the thermodynamically stable products after irradiation as well as the influence of ammonia on the mechanism and products during irradiation.…”

“…The interaction between radicals P and the carba- Intermediate radical products as well as CCl, can be hydrogen acceptors in reactions [15]- [19] and r211.…”

“…Reactions [15]- [21] indicate the role played by radical P in the formation mechanism of products 23, 27, 24, and 26. Reactions involving radicals P have been thoroughly studied previously (33).…”