Effect of Cheiate Formation on the Ozone Decoloration Reaction of Azo Dyes

Abstract

The decoloration reactions of 1-(4-sulfo-1-naphthylazo)-2-naphthol-3, 6 -disulfonic acid (SNND) and 1-(2-hydroxy-4-sulfo-1-naphthylazo)-2-naphthol-3, 6-disulfonic acid (HSNND)by ozone were studied in aqueous media, and the effects of chelate formation of the dyes with Cu(II), Ca(II) and Mg(II) ions were examined. The decoloration of HSNND by ozone was retarded by the chelate formation of HSNND with the metal ions, and the degree of retardation increased with an increase of the value of the formation constant of HSNND-M(II)chelates. The decoloration rate of SNND by ozone, however, increased in the case of the chelate formation with Cu(II). Difference between the behavior of HSNND-Cu(II) and that of SNND-Cu(II) in the ozone decoloration seems to be partly due to the difference in the steric hindrance of these chelates for an ozone attack.