Abstract
Polarographic half-wave potentials E1/2 of some disperse azo dyes were measured in dioxane Britton-Robinson's buffer solution (3: 7) at pH 5.0. The relation between the chemical structure and the E1/2 were studied.
1. [E1/2] of the disperse azo dyes and their model compounds were measured by extrapolating their concentration to zero.
2. [E1/2] attributed to the nitro groups of azo dyes were -0.553_??_-0.705 volt.
Nucleophilic groups increased (-[E1/2]) while electrophilic groups decreased it.
(-[E1/2]) of dyes of this type were considerably lower than that of monosubstituted nitrobenzene.
3. [E1/2] attributed to the azo groups of azo dyes without nitro groups were -0.444_??_-0.999 volt and lower than that of azo benzene (-0.404).
This is because the dyes have some nucleohilic groups.
(-[E1/2]) of 4′-×-4 amino (or oxi) azo benzene were plotted for Hammett's σ. The inclination of the line was minus.
4. It seems resonable to assume that [E1/2] of the disperse azo dyes with nitro group has a relation to the high affinity of dyes _??_or ester graup in fibers.
