Photodissociation of Chalcogenides: Laser Flash Photolysis and Product Analysis Study

JUAN E. ARGÜELLO; ANDREA BARRIONUEVO; LYDIA M. BOUCHET; LUCIANA C. SCHMIDT; ALICIA B. PEÑÉÑORY

la serena

Congreso; X Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2010

The photochemistry of thioethers has been somewhat sparsely studied over the years; in general, aliphatic thioethers undergo homolytic dissociation, both in solution and in the gas phase. Photohomolysis of aryl thioeters may be followed by in-cage electron transfer to give an ion pair.[i] Selenides and tellurides have been used as a source of ketones by irradiation in the presence of molecular oxygen.[ii] However, systematic investigation or basic data such as quantum yields measurement and kinetic information for chalcogenides are scarce at present. To broaden understanding of the photochemistry of the C-S or C-Se moiety, we present our results on the irradiation of a series of aryl diphenylmethyl sulfides and selenides, such as ArSCHPh2 and ArSeCHPh2. Electron-donating and electron-withdrawing groups were included in the aromatic ringfor the sulfides, while for the selenides, phenyl, anisyl and naphthyl derivatives were studied. The involvement of the intermediates Ph2CH•, ArS• and ArSe• was identified using laser flash photolysis (266 nm). Product analysis (254 nm) gives as a main product 1,1,2,2-tetraphenylethane with the formation of a new carbon-carbon bond  and diaryldichacogenides as a main products. All these compounds are formed from the radicals through a coupling reaction. To a lesser extent, H-abstraction products were also observed. References [i] (a) Bonesi, S. M.; Fagnoni. M.; Dondi, D.; Albini, A. Inorg. Chim. Acta 2007, 360, 1230-34. (b) Fleming, S. A.; Jensen, A. W. J. Org. Chem. 1993, 58, 7135-37. [ii] (a) Hyugano, T.; Liu, S.; Ouchi, A. J. Org. Chem. 2008, 73, 8861-66. (b) Ouchi, A.; Hyugano, T.; Liu, C. Org. Lett. 2009, 11, 4870-73.