To obtain a new compound useful as a raw material for monomers for polysulfides or polythioesters, or raw material or the like for surfactants or heavy metal scavengers.

This compound is a compound of formula I (R1 and R2 are each H, an alkyl or aryl). The compound of formula I is obtained by reacting tetrathiol of formula II with a compound of formula III (e.g. acetone), in the presence of a boron trifluoride ether complex, in an organic solvent such as chloroform. The above reaction is desirable to be carried out at 10-5°C for 1-6 h before and after addition of the above-mentioned boron trifluoride ether complex, and thereafter at room temperature. The compound is useful as a raw material for producing compounds each having a new skeleton.