Generation and Decay of Aryl Sulfinyl and Sulfenyl Radicals:  A Transient Absorption and Computational Study

Abstract

Absorption spectra and extinction coefficients of phenylsulfinyl and phenylsulfenyl (thiyl) radicals are determined by nanosecond laser photolysis in various solvents. Direct observation and characterization of arylsulfinyl radicals from the photolysis of several aromatic sulfoxides provides the strongest evidence to date for R-cleavage as the predominant primary photochemical process for these compounds. The absorption spectrum of phenylsulfinyl, with λ max ) 300 and 450 nm and ) 1.1 × 10 4 and 1.3 × 10 3 M -1 cm -1 , is practically independent of solvent. Quantum yields of free sulfinyl radicals range from 0.09 to 0.18 in various solvents. Recombination rate constants very near diffusion control indicate that there is a large spin-orbital coupling in the radical pair. Rate constants for the reactions of arylsulfinyl radicals with stable nitroxide radicals are among the fastest known, but reactivity with O 2 is very modest. Computations indicate that the singly occupied molecular orbital is a π* orbital largely localized on the sulfur and oxygen atoms.

H‐transfer reaction during decomposition of N‐(2‐methylpropyl)‐ N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐N‐oxyl (SG1)‐based alkoxyamines

“…It should be mentioned that the reaction mechanism of thiophenol with nitroxides is rather complicated and is not shown on Scheme in details. In particular, formed PhS · radical can react with nitroxides with formation of amines and other products 34–36. Although it does not affect the alkoxyamine decomposition mechanism and kinetics, thiophenol reacts rapidly with alkyl radicals (reaction vii, Scheme ) suppressing the back recombination.…”

Charge Transfer Interactions in the Generation of Singlet Oxygen O2(1Δg) by Strong Electron Donors

“…30 Solutions were excited in a 1 cm quartz cell by unfocused laser pulses (λ ex ) 266 or 355 nm, 5 ns, 5 SCHEME 1…”

Electron transfer reactions of organic sulfoxides with photochemically generated ruthenium(III)–polypyridyl complexes

“…30 Jenks and co-workers have established that the photolysis of aromatic sulfoxides leads to a-cleavage as the predominant primary photochemical process. 31 The formation of sulfone as the major product of the reaction helps us to conclude that the major portion of sulfoxide radical cation is consumed by the solvent, water, though fragmentation and back ET may be competing processes. The formation of sulfone from sulfoxide radical cation may be shown as three-step process (Eqs.…”