The compound of the formula (II') can also be produced by reacting a compound of the formula: ##STR28## wherein Z1, R13 and m are as defined above, with a sulfonating agent, followed by neutralization to yield a compound of the formula: ##STR29## wherein M is an alkali metal atom, an ammonium group or a residue of an organic base; Z1, R13 and m are as defined above, reacting the compound of the fo