The reactions of sulfur atoms with propadiene and 1,2-butadiene

The gas phase reactions of both S( 1 D) and S( 3 P) atoms with propadiene afford methylenethiirane in nearly quantitative yields at high pressure. With 1,2-butadiene the three novel unsaturated isomeric thiirane products, resulting from addition to the 2,3 double bond and cis- and trans-addition to the 1,2 double bond, have been characterized. The yields are pressure and exposure-time dependent and, at zero conversion and high pressures, comprise ~94% of the C 4 H 6 S adducts, the remainder being two thiol insertion products. The ratio of 2,3-addition to 1,2-addition is ~1.3 forS( 1 D) atoms and ~2.1 for S( 3 P) atoms. Rate parameters for the S( 3 P) + 1,2-butadiene reaction were determined in competition with the S( 3 P) + 1-C 4 H 8 reaction and found to be A = 6.4 ± 1.1 × 10 10 M −1 s −1 and E a = 1.4 ± 0.2 kcal mol −1 . The E a 's associated with 1,2- and 2,3-addition are comparable but the preexponential factors are slightly different.