Reactivity of Electronically Excited SO2 with Alkanes

We studied the reaction of electronically excited sulfur dioxide in the triplet state ((SO2)-S-3) with a variety of alkane species, including propane, n-butane, isobutane, n-pentane, n-hexane, cyclohexane, n-octane, and n-nonane. Reaction rate constants for the photoinitiated reaction of SO2 with all of these species were determined and found to be in the range from 3.7 x 10(-13) to 5.1 x 10(-12) cm(3)molecule(-1)s(-1). We found that reaction proceeds via a hydrogen abstraction to form HOSO center dot and organic radical (R center dot) species and that reactivity is correlated with the energy required to break a C-H bond and the length of the alkane chain. Abstraction rates were found to be fastest for reaction with hydrogen on a tertiary carbon. Similarly, abstraction from secondary carbons is found to be faster than from primary carbons. The reactivity of (SO2)-S-3 with alkanes increases with chain length as additional secondary carbons are added.