Cupric Complexes of Some Ortho-hydroxy Azo-dyes: Part I.

The paper deals with the study of the cupric complexes of some substituted hydroxy azo-dyes, viz., 6-hydroxy-azobenzene-3-methyl-4'-sulphonic acid (abbreviated to 3-Me-4'-sulphodye), 4'-Me-3-sulpho dye and 3-sulpho dye.

This investigation has been carried out to study the effects of a methyl and a sulphonic acid group on the pK_a values of the dyes and the stability constants of their cupric complexes.

The method of synthesis of the dyes and the dye-intermediate p-sulphophenol has been described in this paper. The composition of the cupric complexes were investigated conductometrically and confirmed spectrophotometrically. Jobs' method of continuous variations and mono-variation methods established the formation of 1:2 (ML2) as the highest cupric complex.

The values of pKa are 8.75, 7.72 and 7.53 respectively. The values of log K₁ are found to be 6.14, 6.07 and 6.08 and those of log K₂ are 4.61, 4.43 and 4.42 respectively. The stability constants have been calculated by using Janseen's method with suitable modifications.