Comparison of the photochemistry of diarylchloronium, diarylbromonium, and diaryliodonium salts

Abstract

The direct and triplet-sensitized photochemistry of diphenylchloronium, diphenylbromonium, bis(4methylphenyl)chloronium, and bis(4-methylphenyl)bromonium salts was studied. Direct photolysis of the diarylhalonium salts gave haloarene 2-, 3-, and 4-halobiaryls, and acetanilide, predominantly from a heterolytic cleavage mechanism via the aryl cation-haloarene pair, via in-cage recombination and cage-escape reactions. However, triplet-sensitized photolysis gave haloarene, 2-, 3-, and 4-halobiaryl, and reduced arene mainly from homolytic cleavage to the arene radical-haloarene radical cation pair, which ¿so gave in-cage recombination and cage-escape products. There is evidence for singlet-triplet interconversion of the excited states by spin-orbit coupling and interconversion of the singlet-triplet radical pairs by spin-spin coupling. In addition, electron transfer between the singlet arene cation-haloarene and arene radical-haloarene radic¿ cation pairs is also possible. The effect of halogen and arene substituent on these interconversions is discussed.

Photoinitiated cationic polymerization of epoxy alcohol monomers

“…There is also evidence for the formation of aryl cations. 6,7 as shown in eq 2. The formal initiation reaction involves the direct protonation of the epoxide oxygen by the Brønsted acid as shown in eq 3.…”

The discovery and development of onium salt cationic photoinitiators

“…[13][14][15] The actual mechanism is quite complex; however, for the sake of brevity, it is shown in eq 7 in a highly abbreviated form. The mechanism involves first photoexcitation of the diaryliodonium salt and then the decay of the resulting excited singlet state with both heterolytic and homolytic cleavages of the carbonOiodine bond.…”

Synthesis and photopolymerization of vinyl ether and epoxy-functionalized silicones

“…The reactivity of the novel monomers was obtained using real-time infrared spectroscopy (RTIR). 20 In these studies, the decrease in IR bands at 1210 cm -1 (vinyl ether C-O-C), 1630 cm -1 (vinyl ether double bond), and 810 cm -1 (epoxy) assigned to monomers were followed continuously as a function of time. Because many of the monomers were found to be highly reactive, it was found necessary to adjust the light intensity to a low level (1100 mJ/cm 2 ½ min) to slow the polymerization sufficiently to allow data collection and to facilitate direct comparison of their rates.…”