wherein R1 and R2 are a hydrogen atom or a linear or branched monohydroxyalkyl group having 2 to 3 carbon atoms and at least one of R1 and R2 represents a linear or branched monohydroxyalkyl group having 2 to 3 carbon atoms; and R3 represents a hydrogen atom, an alkali metal atom, an ammonium, or an organic ammonium. 2.