The estimation, with titanium (III) chloride, of azo dyes containing a 3-carboxypyridinium group

The strengths of a number of monoazo dyes, each containing a (3-carboxypyridinium) triazinyl reactive group, were assessed by titrimetric reduction of the azo groups with a standard solution of titanium (III) chloride. The results obtained by this method initially appeared at variance with those by elemental analysis and to indicate that the strengths of the samples were greater than 100%. Further investigation revealed that the 3-carboxpyridium quaternary salt itself, in addition to the azo group, was being reduced, probably to an N-triazinyl dihydropyridine.