The reactions of methanesulfenyl chloride and dimethyl (methy1thio) sulfonium fluoroborate with 2-propenyl methyl sulfide, 3-butenyl methyl sulfide, and 4-pentenyl methyl sulfide are described. Addition to the double bond occurs in each case. l-Chloro-2, 3-bis (methylthio) propane is the kinetic product of addition of CH3SC1 to 2-propenyl methyl sulfide, and this product rearranges on heating at 100" C for 2-3 days to an equilibrium 34: 66 mixture of 1- ...