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

The gas phase reactions of both S(1D) and S(3P) 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 C4H6S adducts, the remainder being two thiol insertion products. The ratio of 2,3-addition to 1,2-addition is ~1.3 forS(1D) atoms and ~2.1 for S(3P) atoms. Rate parameters for the S(3P) + 1,2-butadiene reaction were determined in competition with the S(3P) + 1-C4H8 reaction and found to be A = 6.4 ± 1.1 × 1010 M−1 s−1 and Ea = 1.4 ± 0.2 kcal mol−1. The Ea's associated with 1,2- and 2,3-addition are comparable but the preexponential factors are slightly different.