Photochemical Oxidation of Thioketones by Singlet Molecular Oxygen Revisited: Insights into Photoproducts, Kinetics, and Reaction Mechanism

Abstract

Photosensitized oxidation of trimethyl[2.2.1]bicycloheptane thioketones by (1)O2 can yield more photoproducts than exclusively ketones and sulfines. Moreover, the ketone/sulfine ratio can be reversed when protic conditions and high thioketone concentrations are used, conversely to earlier results reporting ketones as the main photoproducts. A new mechanistic proposal for sulfine formation is suggested following intermolecular oxygen transfer from a peroxythiocarbonyl intermediate to a second thioketone molecule. Reaction quantum yields (10(-5)-10(-2)) depend on the reaction conditions and time. Sulfine production reaches a maximum at short irradiation times, whereas decomposition to the corresponding ketone is observed at long reaction times. When the thioketone substrate has a hydrogen atom at the α position a peroxyvinylsulfenic acid intermediate can be formed by proton transfer. Reaction of this intermediate with another thioketone molecule can yield more sulfine and its tautomeric vinylsulfenic acid, which dimerizes in situ to the thiosulfinate. The hydroperoxyl group of the peroxyvinylsulfenic acid can also rearrange to the α position, and by reaction with the starting thioketone, α-hydroxy thioketone and additional sulfine can be formed, while dehydration yields the α-oxo thioketone. In situ [2 + 2] and [4 + 2] self-cycloaddition of the α-oxo thioketone yields significant amounts of the corresponding adducts at prolonged irradiation times.

Insights Into the Mechanism of Energy Transfer with Poly(Heptazine Imide)s in a Deoximation Reaction

“…The investigation started from varying the conditions of 1 i conversion into 2 i (Figure 2). Taking into account extensive study of photochemical (without added catalyst) C=X bonds cleavage under visible light irradiation, [21,22] four sets of experiments were performed under blue (461 nm), green (525 nm) and red (625 nm) LED irradiation, as well as the control set in the dark.…”

5-Iodo-4-thio-2′-Deoxyuridine as a Sensitizer of X-ray Induced Cancer Cell Killing

“…The oxidation products, ISOU and SU, usually result from the reaction with singlet oxygen formed via photochemical oxidation [26,27,28]. Yet, singlet oxygen does not form during irradiation with IR, as was indicated by the X-ray studies on silicon nanoparticles involving a fluorescence probe for singlet oxygen [29].…”

Visible‐Light‐Induced Passerini Multicomponent Polymerization

“…Evident in the SEC traces depicted in Figure (orange line, M w 1290 g mol −1 , M n 640 g mol −1 ), there are trace amounts of oligomers remaining. This is attributed to a very small number of ester linkages, instead of thioester linkages, caused by photooxidation of C 2 into neopentyl aldehyde during polymerization (see Figure S8, structures 5 and 10) . We also analyzed the degradation products by high‐resolution ESI‐MS (see Figure S9) where the two primary degradations products (Scheme , right‐hand side) can clearly be identified.…”