Process for purification of water soluble dyes via water insoluble metal salt intermediate

摘要

An invention is disclosed which pertains to a method for purifying water soluble dyes, such as quinoline, fluoran, and xanthene dyes. The method comprises the steps of A) adding a metal salt to the water soluble dye to form a water insoluble dye salt of the metal; B) isolating the water insoluble dye salt of step A; C) converting the water insoluble dye salt of step B into a water soluble dye solution; and D) isolating the water soluble dye from the solution of step C. The present invention teaches a straight forward, economical, and environmentally sound method for purifying water soluble dyes of FDA certifiable purity and with an aesthetically improved shade.