Preparative purification of 4-hydroxy-1-naphthalenesulfonic acid sodium salt by high-speed counter-current chromatography

Among the many applications of 4-hydroxy-1-naphthalenesulfonic acid sodium salt (HNSA, CAS No. 6099-57-6) is its use as a common intermediate in the manufacture of dyes used as color additives. In order to develop an HPLC method to analyze HNSA in such additives, it was necessary to obtain pure HNSA as a reference material. This compound is only commercially available in “technical” or “practical” grade (∼70–85% purity). Unsatisfactory results were encountered during the attempts to eliminate impurities using published preparative purification methods. The current work demonstrates the successful application of high-speed counter-current chromatography (HSCCC) to the preparative purification of “practical” grade HNSA. The purifications of 0.55 g and 1.00 g portions were achieved by using a solvent system that consisted of n-butanol/water (1:1), acidified with 0.2% trifluoroacetic acid. In contrast to the procedure involved in previous HSCCC separations of aromatic sulfonates, it was not necessary to add a ligand and a retainer to the solvent system for these separations. The resulting yields were 320 mg and 485 mg of HNSA, respectively, of over 99% purity. Elemental analysis, HPLC (at 240 nm), UV and high-resolution MS analyses confirmed the identity and purity of the HNSA obtained.