. . . . . . " sodium or potassium, an alkali earth metal atom such as calcium or magnesium, or an organic base such as trimethylamine or triethylamine; X represents an alkyl group having 1 to 6 carbon atoms, an alkoxy group, an alkylamino group, or a halogen atom; m represents 0, 1 or 2; and n represents 1 or 2." .