RESUMEN

Photoinduced deoxygenation of dibenzothiophene S-oxide (DBTO) has been suggested to release atomic oxygen [O((3)P)]. To expand the conditions and applications where O((3)P) could be used, generation of O((3)P) at longer wavelengths was desirable. The sulfoxides benzo[b]naphtho-[1,2,d]thiophene S-oxide, benzo[b]naphtho[2,1,d]thiophene S-oxide, benzo[b]phenanthro[9,10-d]thiophene S-oxide, dinaphtho[2,1-b:1',2'-d]thiophene S-oxide, and dinaphtho[1,2-b:2',1'-d]thiophene S-oxide all absorb light at longer wavelengths than DBTO. To determine if these sulfoxides could be used to generate O((3)P), quantum yield studies, product studies, and computational analysis were performed. Quantum yields for the deoxygenation were up to 3 times larger for these sulfoxides compared to DBTO. However, oxidation of the solvent by these sulfoxides resulted in different ratios of oxidized products compared to DBTO, which suggested a change in deoxygenation mechanism. Density functional calculations revealed a much larger singlet-triplet gap for the larger sulfoxides compared to DBTO. This led to the conclusion that the examined sulfoxides could undergo deoxygenation by two different mechanisms.

Asunto(s)

Oxígeno/química , Procesos Fotoquímicos , Sulfóxidos/química , Tiofenos/química , Benceno/química , Estructura Molecular , Oxidación-Reducción , Solventes/química , Análisis Espectral , Tolueno/química , Rayos Ultravioleta

RESUMEN

Photolysis of aromatic sulfoxides in the presence of alkoxides in alcoholic solvents provides a photochemical route to the corresponding sulfides. Other electron donors also give sulfide with various degrees of success. The reaction could also be carried out using carbazoles as sensitizers, and quantitative yields could be obtained using N-methylcarbazole in methanol. Evidence points toward a hydroxysulfuranyl radical as the key intermediate, and solvent effects point to heterolysis, rather than homolysis, as the step that breaks the S-O bond.

RESUMEN

Gas-phase activation data were obtained for model sulfoxide elimination reactions. The activation enthalpy for methyl 3-phenylpropyl sulfoxide is 32.9 +/- 0.9 kcal/mol. Elimination by methyl vinyl sulfoxide to form acetylene has an enthalpic barrier of 41.6 +/- 0.8 kcal/mol and that of 3-phenylpropyl methanesulfinate to form hydrocinnamaldehyde is 34.6 +/- 0.6 kcal/mol. Calculations at the MP2/6-311+G(3df,2p)//MP2/6-31G(d,p) level for simplified models of these reactions provide barriers of 32.3, 40.3, and 32.7 kcal/mol, respectively. A series of other compounds are examined computationally, and it is shown that the substituent effects on the sulfoxide elimination reaction are much more straightforward to interpret if DeltaH data are available in addition to the usually determined DeltaH++. The activation enthalpy of the reverse addition reaction is also subject to structural variation and can usually be rationalized on the basis of nucleophilicity of the sulfur or polarity matching between the sulfenic acid and olefin derivative.