Rates of Reaction of Singlet Oxygen With Sulfides

Abstract

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.

Photochemical Estimation of Oxygen Solubility

“…The measured fluorescence lifetime of rubrene photoinitiated side reactions might be a problem. in air-saturated chloroform was found to be concentration Since fluorescence lifetimes are determined, the rate Determinaton of solubility constant, Rubrene was dis-is consumed' The Oxygen concentration is to where the former cannot be a merry-go-round apparatus (Monroe, 1979). The samples rubrene has Only limited It does not require…”

“…In the course of our investigation of the rate constant for the reaction of singlet oxygen (lo,)$ with various quenchers and acceptors (Monroe, 1977(Monroe, , 1978(Monroe, , 1979(Monroe, , 1980Monroe and Mrowca, 1979), it was necessary to know the approximate solubility of oxygen in chloroform. Since this constant does not seem to have been reported in the literature, a technique for estimating the solubility constant of oxygen in any solvent in which rubrene (1) is soluble was developed.…”

Structure-Activity Relationships for Photooxidation Processes in the Environment

“…Monroe [45] listed Hammett parameters for nine singlet oxygen reactions [80-871, all of which were conducted in organic solvents. Values of p varied from -0.82 to -1.71, with no obvious relation between reaction type or class and the value of p. In most cases, better correlations were found with u than with u+, and, when similar groups of thioanisole oxidations were examined in methanol [81] and chloroform [82], p values of -1.6 and -1.67 were found. Table 5 lists the reported singlet oxygen SARs.…”

“…Steric effects also can be important in some singlet oxygen reactions. Monroe [81] reported that for the series of dialkyl sulfides, R2S, where R varies from Me to t-Bu and Ph, values of k,, (for reaction) decreased by over 300 times. Analysis of his data using only the Taft E, values for R gave a fair correlation of five sulfides, with 6 = 0.46 and r2 = 0.78.…”

The Photooxygenation of Benzyl, Heteroarylmethyl, and Allyl Sulfides

“…[15a] Noteworthy, the ratio k r /k T , which may be taken as a rough esticreases k T by a factor of 3.5 in thioanisole, [12] by a factor of 1.45 in benzyl sulfide 1). Table 2 shows that quenching mate of the propensity of the persulfoxide to react chemically rather than decay to the components, only marginally is little solvent-dependent, as is generally assumed [8] to be the case for alkyl sulfides.…”