Preparative separation of di- and trisulfonated components of Quinoline Yellow using affinity-ligand pH-zone-refining counter-current chromatography

Four positionally isomeric 2-(2-quinolinyl)-1H-indene-1,3(2H)-dionedisulfonic acids (SA) and one triSA, components of the color additive Quinoline Yellow (QY, Color Index No. 47005), were isolated from the dye mixture by affinity-ligand pH-zone-refining counter-current chromatography (CCC) through complementary use of ion-exchange and ion-pair reagents as the ligand. The added ligands facilitated the partitioning oft lie very polar polysulfonated components into the organic stationary phase of the two-phase solvent systems that consisted of isoamyl alcohol-methyl tert-butyl ether-acetonitrile-water (3:5:1 :7).(3:4: 1:7) or (3:11:5). Thus. separation of a 5-g portion Of QY using Sulfuric acid as the retainer and dodecylanime as the ligand (an ion-exchange reagent, 20% in the stationary phase), resulted in 1.21 g of 6',5-diSA and 1.69 g of 6',8',5-triSA, both of over 99% purity. A minor component, 8',4-diSA, not previously reported was also obtained (4.8 mg of over 94% purity) through a similar separation of a different batch Of QY using hydrochloric acid as the retainer and 10% dodecylamine as the ligand in the stationary phase. Two components that co-eluted (0.55 g) in the 5 g separation were separated when trifluoroacetic acid was used as the retainer and tetrabutylammonium hydroxide (an ion-pair reagent) as the ligand. The separation resulted in 20.7 mg of 6',4-diSA, not previously reported, and 111.8 mg of 8'.5-diSA, both of over 98% purity. The isolated Compounds were characterized by high-resolution mass spectrometry and proton nuclear magnetic resonance with correlated spectroscopy assignments. Published by Elsevier B.V.