80.5 parts of 1,4-bis(hydroxyethylsulfonylmethyl)benzene are stirred into 612.5 parts of 100% strength sulfuric acid, and the mixture is heated at 35° to 40° C. until a sample shows quantitative esterification in the HPLC chromatogram (about 4 to 5 hours). 57 parts of a mixture of 30 parts by weight of 100% strength nitric acid and 70 parts by weight of 100% strength sulfuric acid (so-called "M3 acid") are then added dropwise over a period of 4 hours at 30° to 40° C., stirring is continued for 2 hours at 45° C. until the nitration is completed (checked by HPLC chromatogram), and the reaction mixture is then decomposed by pouring it into 2,500 parts of cold water. The resulting aqueous acidic solution is then refluxed (about 110° C.) for 5 hours to hydrolyze the sulfuric ester groups, 5 parts of activated carbon are then added, the mixture is clarified and the clarified filtrate is cooled to 0° to 5° C. with stirring. The resulting precipitate is filtered off with suction, washed neutral and dried in vacuo at 80° C. This gives 89.0 parts of 2,5-bis(hydroxyethylsulfonylmethyl)nitrobenzene of the formula ##STR20## in the form of colorless crystals of melting point 125° to 126.5° C., the purity of which (HPLC) is 98.8%.
