Reactivity of Electronically Excited SO2 with Alkanes.

We studied the reaction of electronically excited sulfur dioxide in the triplet state (3SO2) 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 × 10-13 to 5.1 × 10-12 cm3molecule-1s-1. We found that reaction proceeds via a hydrogen abstraction to form HOSO• and organic radical (R•) 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 3SO2 with alkanes increases with chain length as additional secondary carbons are added.