Radical cleavage and competing photoreactions of phenacyl sulfides

Journal Article · Wed May 13 04:00:00 EDT 1987 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00244a032· OSTI ID:6540015

Wagner, P J; Lindstrom, M J

The photochemistry of ketones with the structures PhCOCH/sub 2/SR, PhCOCH/sub 2/S(O)R, PhCOCH/sub 2/SO/sub 2/R, and p-X-PhCOCH/sub 2/SPh has been studied. They all give primarily acetophenone as product when irradiated in the presence of benzenethiol, which traps free phenacyl radicals formed by excited state ..beta..-cleavage. The sulfur-centered radicals give coupling products. The maximum quantum yield for this ..beta..-cleavage is 0.40; apparently 60% of the initially formed radical pairs undergo in-cage reaction. When R = methyl or butyl, some acetophenone is formed by ..gamma..-hydrogen abstraction as well. Alkyl substituents on the ..cap alpha..-carbon enhance the disproportionation reactions of the phenacyl radicals. Measurements of quantum yields and triplet lifetimes (by Stern-Volmer quenching of acetophenone formation) allowed determination of rate constants for ..beta..-cleavage as follows: PhS, 10/sup 10/-10/sup 11/; MeS(O), 6 x 10/sup 9/; BuS, 1.5 x 10/sup 8/; BuSO/sub 2/, 1 x 10/sup 7/ s/sup -1/. Ring substituents increase triplet lifetimes. Absorption and phosphorescence spectra and indicate that the n,..pi..* and ..pi..,..pi.. transitions both involve some population of the C-S sigma* orbital. This mixing, together with the free spin density on the excited carbonyl carbon, appears to determine the rate constant for cleavage. Radical cleavage is also very fast and efficient for p-((phenylthio)methyl)acetophenone.

• Research Organization: Michigan State Univ., East Lansing
• OSTI ID: 6540015
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:10; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ABSORPTION SPECTROSCOPY
ACETOPHENONE
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
EFFICIENCY
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
INFORMATION
KETONES
KINETICS
LIFETIME
LUMINESCENCE
MULTIPLETS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOSPHORESCENCE
PHOTOCHEMICAL REACTIONS
QUANTUM EFFICIENCY
RADICALS
REACTION KINETICS
SPECTROSCOPY
SULFIDES
SULFUR COMPOUNDS
SYNTHESIS
TRIPLETS