Warner-jenkinson Company, Inc.

Puthalath K Sujeeth

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.

Process for purification of water soluble dyes via water insoluble metal

A process for the manufacture of fluorescein compounds suitable for conversion to FDA certified dyes is described. The fluorescein compounds, and in particular fluorescein (also known as Solvent Yellow 94 or D&C Yellow No.7) and 3,4,5,6-tetrachlorofluorescein, are made by a process involving the condensation of a phthalic anhydride with several molar excess of a resorcinol, the resorcinol being employed not only as a reactant, but also as a solvent for the reaction. This process also can employ the unreacted resorcinol and any intermediates or by-products from the condensation reaction as a reactant and as a solvent in subsequent condensation reactions.

Syntheses of fluorescein compounds with excess resorcinol as a solvent

A process for the manufacture of a quinophthalone, in particular Solvent Yellow 33 (D & C Yellow 11) is described. The quinophthalone, in particular Solvent Yellow 33, is made by a process in which quinaldine is condensed with a molar excess of either phthalic acid or phthalic anhydride, the acid or anhydride being employed not only as a reactant, but also as a solvent for the reaction. This process can also employ phthalic acid (or recycled phthalic acid) and phthalic anhydride together, one as the solvent and the other as the reactant.

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Maryland Heights, MO, United States of America

Puthalath K Sujeeth