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Photosensitized oxidation of aryl benzyl sulfoxides. Evidence for nucleophilic assistance to the C-s bond cleavage of aryl benzyl sulfoxide radical cations. (Articolo in rivista)

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Photosensitized oxidation of aryl benzyl sulfoxides. Evidence for nucleophilic assistance to the C-s bond cleavage of aryl benzyl sulfoxide radical cations. (Articolo in rivista) (literal)

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Del Giacco, Tiziana; Lanzalunga, Osvaldo; Lapi, Andrea; Mazzonna, Marco; Mencarelli, Paolo (2015)
Photosensitized oxidation of aryl benzyl sulfoxides. Evidence for nucleophilic assistance to the C-s bond cleavage of aryl benzyl sulfoxide radical cations.
in Journal of organic chemistry; American Chemical Society, Washington (Stati Uniti d'America)
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Del Giacco, Tiziana; Lanzalunga, Osvaldo; Lapi, Andrea; Mazzonna, Marco; Mencarelli, Paolo (literal)

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+Dipartimento di Chimica, Biologia e Biotecnologie and Centro di Eccellenza Materiali Innovativi Nanostrutturati, Universita? di Perugia, via Elce di sotto 8, 06123 Perugia, Italy ?Dipartimento di Chimica and Istituto CNR di Metodologie Chimiche-IMC, Sezione Meccanismi di Reazione c/o Dipartimento di Chimica, Sapienza Universita? di Roma, P.le A. Moro 5, 00185 Rome, Italy (literal)

Titolo

Photosensitized oxidation of aryl benzyl sulfoxides. Evidence for nucleophilic assistance to the C-s bond cleavage of aryl benzyl sulfoxide radical cations. (literal)

Abstract

The radical cations of a series of aryl benzyl sulfoxides (4-X-C6H4CH2SOC6H4Y(+)) have been generated by photochemical oxidation of the parent sulfoxides sensitized by 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-)). Steady-state photolysis experiments showed the prevailing formation of benzylic products deriving from the C-S fragmentation in the radical cations, together with sulfur-containing products. Formation of sulfoxide radical cations was unequivocally established by laser flash photolysis experiments showing the absorption bands of 3-CN-NMQ() (lambdamax = 390 nm) and of the radical cations (lambdamax = 500-620 nm). The decay rate constants of radical cations, determined by LFP experiments, decrease by increasing the electron-donating power of the arylsulfinyl Y substituent and to a smaller extent by increasing the electron-withdrawing power of the benzylic X substituent. A solvent nucleophilic assistance to the C-S bond cleavage has been suggested, supported by the comparison of substituent effects on the same process occurring in aryl tert-butyl sulfoxide radical cations. DFT calculations, performed to determine the bond dissociation free energy in the radical cations, the transition state energies associated with the unimolecular C-S bond cleavage, and the charge and spin delocalized on their structures, were also useful to endorse the nucleophilic assistance to the C-S scission. (literal)

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