Process for producing episulfide compound for optical material, episulfide-containing composition, and polymerizable composition for optical material including the same composition

A process for producing an episulfide-containing composition, comprising:

• a step of chlorinating glycerin in a composition a including the glycerin obtained from plant-derived materials to obtain a composition b including dichloropropanol;
• a step of epoxidizing the dichloropropanol in the composition b to obtain a composition c including epichlorohydrin;
• a step of reacting the epichlorohydrin with a sulfating agent in the composition c to obtain a composition d including a bis(chlorohydrin) (di)sulfide compound through a thiol compound;
• a step of epoxidizing the bis(chlorohydrin) (di)sulfide compound under basic conditions in the composition d to obtain a composition e including an epoxy compound;
• and
• a step of reacting the epoxy compound with a sulfating agent in the composition e to obtain a composition f including an episulfide represented by following General Formula (1):
• wherein, in the formula, n represents 0 or 1,
• wherein the step of chlorinating glycerin in a composition a including the glycerin is a step of chlorinating glycerin to obtain a composition b containing dichloropropanol and chlorine-based byproduct which is at least one compound selected from allyl chloride, 1,2-dichloropropane, 2,3-dichloropropene, 2-chloroallyl alcohol, 1,3-dichloropropene, and 1,2,3-trichloropropane, and
• wherein the step of epoxidizing the dichloropropanol in the composition b is a step of epoxidizing the dichloropropanol in the composition b to obtain a composition c containing epichlorohydrin and 5,000 ppm or less of the chlorine-based byproduct.