Participation of a heterolytic path in the photochemistry of chlorobenzene

Direct photodegradation of lamotrigine (an antiepileptic) in simulated sunlight – pH influenced rates and products

“…1A). Chlorinated arenes (like LTG's dichlorophenyl ring) have been observed to undergo photochemical reactions through excited state charge transfer complexes, 50 and there is at least some potential for LTG 0 and LTG + to form ground state complexes via cation-p bond interactions, 51 but the LTG concentrations used in this study are low (<0.05 mM), and LTG concentrations in the environment are even lower. It is more likely that the reaction quantum yields in Table 1 are affected by small errors in determining the solar simulator's spectral irradiance or LTG's molar absorptivity, particularly at pH 3.3 and 5.3 where their spectral overlap is small (Fig.…”

On the Route to the Photogeneration of Heteroaryl Cations. The Case of Halothiophenes

“…Furthermore, the products of the reaction with allyltrimethylsilane and those with hexamethylbenzene are typical markers of a triplet aryl cation and are best rationalized as resulting from electron transfer (ET) within the thienyl and halogen radical pair [ 14 • X • ] 3 . This leads indirectly to ion 3 14 + (Scheme , path g) , which is trapped by π-bond nucleophiles to give the arylated products (path h). The formation of aryl cations from an ET mechanism within a radical pair has been sparsely documented, providing that it takes place in a high polar medium (e.g., water). ,, Notice further that 5-uracyl and 5-citosyl cations have been invoked when investigating the reactivity of 5-fluorouracil and 5-bromocytosine, respectively, where the heteroaryl radical intermediate was oxidized by the radical cation of N α -acetyl- l -tryptophan N -ethylamide. , More relevant to the present case, the formation of the parent triplet phenyl cation from the corresponding aryl radical has been previously postulated in the photodechlorination of chlorobenzene .…”

“…This leads indirectly to ion 3 14 + (Scheme , path g) , which is trapped by π-bond nucleophiles to give the arylated products (path h). The formation of aryl cations from an ET mechanism within a radical pair has been sparsely documented, providing that it takes place in a high polar medium (e.g., water). ,, Notice further that 5-uracyl and 5-citosyl cations have been invoked when investigating the reactivity of 5-fluorouracil and 5-bromocytosine, respectively, where the heteroaryl radical intermediate was oxidized by the radical cation of N α -acetyl- l -tryptophan N -ethylamide. , More relevant to the present case, the formation of the parent triplet phenyl cation from the corresponding aryl radical has been previously postulated in the photodechlorination of chlorobenzene . The formation of a small amount of trifluoroethoxythiophene ( 2e′ ) in TFE is best justified via ISC from triplet to singlet thienyl cation ( 1 14 + , Scheme , path i) .…”

“…30 Furthermore, the products of the reaction with allyltrimethylsilane and those with hexamethylbenzene are typical markers of a triplet aryl cation and are best rationalized as resulting from electron transfer (ET) within the thienyl and halogen radical pair [14 • X • ] 3 . This leads indirectly to ion 3 14 + (Scheme 5, path g) 10,31 which is trapped by π-bond nucleophiles 32 to give the arylated products (path h). The formation of aryl cations from an ET mechanism within a radical pair has been sparsely documented, providing that it takes place in a high polar medium (e.g., water).…”

“…These photochemical reactions are efficient when irradiating, in polar protic solvents, aryl chlorides substituted with strong (NH 2 , NMe 2 , OH, OMe, CH 2 SiMe 3 ) , or mild (alkyl, SiMe 3 ) electron-donating groups . In highly ion-stabilizing 2,2,2-trifluoroethanol (TFE), heterolysis of the Ar–Cl bond can likewise take place in parent chlorobenzene or in 4-chlorobenzaldehydes and acetophenones when protected as 1,3-dioxolanes . Recently, we demonstrated that the likelihood of the photoheterolysis step was established through DFT calculations evaluating the geometry, the spin, and charge distribution on the benzene ring of the aromatic in its triplet state ( 3 ArX) .…”