Rates of Reaction of Singlet Oxygen With Sulfides

Abstract—Reaction rate constants for the reaction of singlet oxygen with a series of 24 sulfides in chloroform have been measured by inhibition of the self‐sensitized photooxidation of rubrene. The reaction rate constant is sensitive to steric effects, decreasing as the carbons α‐ to sulfur become more highly substituted. Addition of a methyl group to each of the carbons α‐ to sulfur decreases the rate constant by about a factor of 10. From a series of p‐ and m‐substituted thioanisoles, a ρ of ‐1.67 ± 0.09 was found. A much better correlation was found with σ than with σ+ indicating there is no resonance interaction with the reaction center. Typical rate constants are: di‐n‐butyl sulfide, 2.3 × 107M‐1 s‐1; CBZ‐L‐methionine methyl ester, 1.4 × 107; di‐s‐butyl sulfide, 1.8 × 106; di‐t‐butyl sulfide, 1.3 × 105; and thioanisole, 2.3 × 106.