A New Route for the Preparation of 5-Hydroxyisophthalic Acid

A new, simple and practical, two-stage process for the preparation of 5-hydroxyisophthalic acid (5-HIPA) from isophthalic acid is described. In the first stage, isophthalic acid is brominated by bromine in oleum, in the presence of an iodine catalyst, to give crude 5-bromoisophthalic acid (5-BIPA). In the second stage the crude 5-BIPA is hydrolyzed with aqueous NaOH, in the presence of a copper catalyst, to give crude 5-HIPA, with a purity of ca. 98%. Both stages of the process were optimized. A single crystallization of the crude 5-HIPA from water gives the product in a purity of more than 99%. The overall yield of pure 5-HIPA is 65−70%.