Process for the manufacture of symmetric 1:2 chromium complexes of azo dyes
AssigneeCiba-Geigy Corporation
InventorsChristian Wittwer, Emil Bonometti
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Abstract
The present invention relates to a process for the manufacture of 1:2 chromium complexes of metallisable azo dyes, wherein the azo dyes are treated in aqueous solution at pH 7 to 9 with at least the stoichiometric amount of a chromium complex, and, in the course of the chroming, the reaction medium is acidified once or repeatedly to a pH of 6 or less and subsequently brought back again to pH 7 to 9.
Claims5
In a process for the manufacture of 1:2 chromium complexes of metallisable azo dyes, wherein the azo dyes are treated in aqueous solution at pH 7 to 9 with at least the stoichiometric amount of chromium oxalate solution, the improvement comprising acidifying the reaction medium during the course of the chroming once or repeatedly to a pH of 6 or less to reactivate precipitated chromium compounds and readjusting the pH to pH 7 to 9 to complete the metallization process.
Dependencies are inferred from the claim text.