| abstract |
Production of strongly colored 4,4 ', 7,7'-tetrachlorothioindigo pigments by oxidation of 3-hydroxy-4,7-dichlorothionaphthene or a mixture of tetrachlorothioindigo and hydroxydichlorothionaphthene in an aqueous alkaline suspension with aromatic nitrosulfonic acids in the form of the salts and in the presence of high-boiling salts , Aromatic liquids which are not miscible with water at 40 to 100'C and heating the organic suspension to temperatures between 110 and 180 ° C. After isolation, pigment forms of tetrachlorothioindigo are obtained, which give strong colorations with high brilliance in the white blend. |