| abstract |
wherein at least one of R1 and R3 represents SO3− or SO3Y, where Y represents a hydrogen atom, an alkali metal atom, or an alkaline earth metal atom; when not representing SO3− or SO3Y, R1 and R3 represent a halogen atom or a hydrogen atom; R2 and R4 each independently represent a hydrogen atom, a halogen atom, a sulfo group, a nitro group, an aryl group, a sulfonamide group, a carboxy group, an alkyl group of 1 to 4 carbon atoms, SO2NHR5, or COOR5, where R5 represents a hydrogen atom or an alkyl group; and X represents a metal atom. |