Addition of sulphur atoms to double and triple bonds

7 ADDITION OF SULPHUR ATOMS TO DOUBLE AND TRIPLE BONDS 

The stereochemistry of the episulphide formation is of interest, inasmuch as it gives considerable insight into the mechanism. If the sulphur atom addition were stepwise, then the geometry of the initial olefin would not be preserved. In fact, it is, with either triplet or singlet sulphur. This indicates that the formation of the two carbon—sulphur bonds of the episulphide is either simultaneous or so fast a consecutive process as to be more rapid than rotation around a carbon—carbon bond, viz. 

In a similar fashion, the absolute rate coefficients can be obtained for the reaction with propene, but except for the last value in Table 27, the rates are relative. The first value in Table 27 is suspect because singlet sulphur atoms were undoubtedly present in the reaction mixture. 

The absolute rates for 1-butene are given in Table 28, and again these are recalculated from relative rates. They are, however, consistent, although this is not too surprising. After all, if one assumes that the rate data for ethylene are correct, then the inherently more accurate relative rate data will fall into line very nicely. No Arrhenius parameters are available. 

With the 2-butene isomers, the rate is fractionally greater than for 

---