Method for producing methylene disulfonate compound

A method for producing a methylene disulfonate compound, comprising:

• step A of reacting at least one alkanesulfonic acid compound and sulfur trioxide in the presence of sulfolane to thereby obtain reactant A comprising an alkanedisulfonic acid compound, and
• step B of reacting reactant A obtained in step A and a formaldehyde compound in the presence of sulfur trioxide and sulfolane to thereby obtain a methylene disulfonate compound;
• the amount of sulfolane in step A being 0.1 mol or more and 10 mol or less per mol of sulfur trioxide,
• the amount of sulfur trioxide added in step B being 2.0 mol or more and 10 mol or less per mol of the alkanedisulfonic acid compound;
• the alkanesulfonic acid compound being represented by the following formula (1):
• wherein in formula (1), R1 and R2 are the same or different, and each is a C1-4 alkyl group optionally substituted with a halogen atom, or a hydrogen atom;
• and n is an integer of 1 to 4;
• when n is an integer of 2 to 4, n-number of R1 may be the same or different, and n-number of R2 may be the same or different;
• the alkanedisulfonic acid compound being represented by the following formula (4):
• wherein in formula (4), R1, R2, and n are respectively the same as R1, R2, and n in formula (1);
• and
• the methylene disulfonate compound being represented by the following formula (5):
• wherein in formula (5), R1, R2, and n are respectively the same as R1, R2, and n in formula (1).