Method for treating water containing 4, 4 '-dichlorodiphenyl sulfoxide and/or 4, 4'-dichlorodiphenyl sulfone as impurities

The invention relates to a method for treating 4, 4 '-dihydroxybenzaldehyde. The present invention relates to a method for producing water containing 4, 4 '-dichlorodiphenyl sulfoxide and/or 4, 4'-dichlorodiphenyl sulfone as an impurity, comprising: (a) reacting water containing 4, 4 '-dichlorodiphenyl sulfoxide and/or 4, 4'-dichlorodiphenyl sulfone as an impurity with water containing 4, 4 '-dichlorodiphenyl sulfoxide and/or 4, 4'-dichlorodiphenyl sulfone as an impurity in which 4, 4 '-dichlorodiphenyl sulfoxide and/or 4, 4'-dichlorodiphenyl sulfone has at 20 DEG C a water phase based on 4, 4 '-dichlorodiphenyl sulfoxide and/or 4, 4'-dichlorodiphenyl sulfone and/or 4, 4 '-dichlorodiphenyl sulfone as an impurity; the present invention relates to a process for the preparation of 2, 4 '-dichlorodiphenyl sulfone by mixing 2, 4'-dichlorodiphenyl sulfone with an organic solvent having a solubility of at least 0.5 wt%, based on the amount of the organic solvent, which organic solvent forms a two-phase system with w