Investigations on decolorization products of azo dyes by sodium

Decolorization of two ate dyes (C.I. Acid Orange 7 similar to 1a similar to and C.I. Acid Orange 20 similar to 2a similar to by sodium sulfite solution was pursued photometrically at 30 degrees C. The initial decolorization products showing absorption maxima at 413 nm for 1a and 374 nm for 2a were isolated as tetrabutylammonium ion-complexes soluble in organic solvents. The measurements of the H-1-NMR and the two-dimensional COSY spectra revealed that the products were not hydrazobenzene derivatives which had been suggested so far, but Michael adducts of sodium sulfite to hydrate-form of the dyes. The IR data also supported the structures.