Process for preparation of water-soluble dyes containing lithium sulfonate groups or ammonium sulfonate groups.

摘要

In accordance with this invention an aqueous solution of a water-soluble dye containing lithium sulfonate groups or ammonium sulfonate groups can be obtained by a very simple and economical process in such a way that an aqueous solution of a water-soluble dye containing sodium sulfonate groups is fed to a column packed with an acid type cation exchange resin (H-­form) to form an aqueous solution of a dye containing free sulfonic acid groups, and after neutralizing the resulting solution with LiOH or NH₄OH, the aqueous solution of the dye thus obtained is concentrated according to a process for separation through a membrane for reverse osmosis.