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 pKa 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