3-Chloropropionyl chloride → 4-(3-Chloropropionylthiomethyl)-1,3-dithiolane

Into 500 ml glass reactor equipped with a stirrer and a cooling pipe, 91.2 g (0.60 moles) of 4-mercaptomethyl-1,3-dithiolane (2-1) produced in Example 1 was weighed and poured, and 80.0 g (0.63 moles) of 3-chloropropionic chloride was added dropwise into the reactor at 40° C. over 15 minutes. After reacted at 40° C. for eight hours with stirring, 200 g of toluene was added to the reaction mixture to dissolve the mixture. The mixture then was moved into a separating funnel to be rinsed three times with 300 g of 3 wt. % sodium hydrogen carbonate aqueous solution. Then, after the mixture was rinsed with 300 g of pure water until the water layer became neutral, the organic layer (toluene solution) was taken out. Toluene was evaporated off under reduced pressure, and 119 g of 4-(3-chloropropionylthiomethyl)-1,3-dithiolane was obtained as a transparent and colorless liquid.