SPECTROPHOTOMETRIC STUDIES ON FERROUS COMPLEXES OF  QUINOLINE- AND PYRIDINE-CARBOXYLIC ACIDS. PART III.  FERROUS DIPICOLINIC ACID AND FERROUS QUINOLINIC  ACID SYSTEMS

Highly soluble coloured ferrous complexes of dipicolinic and quinolinic acids have been studied by spectrophotometric method. The ferrous cmplexes of some other pyridine di- and tri­carboxylic acids with a carboxyl group in the e-position to the nitrogen atom have also been studied in a qualitative manner. Ferrous dipicolinic acid complex shows its maximum colour intensity between PH 5 and 7 and the Amer at 480 m\(\mu\) The intensity of colour, however, decreases in the presence of KCN or pyridine. The colour system obeys Beer's law, and its composition is given by 1 FeII : a acid, with an instability constant, 1.85 X 10-7. The soluble coloured complex of ferrous quinolinic acid has been found to give its maximum colour intensity between PH 5.7 and 7.0 with \(\lambda\)max at 420 m\(\mu\), and the colour is intensified with the addi­tion of KCN, and to some extent with pyridine. The \(\lambda\)max for cyanide-containing system lies at 440 m\(\mu\). The colour system with or without the cyanide obeys Deer's law under specified conditions. The composition of the complex is represented by 1FeII : 3 acid with an instability constant of 3.47 X I0-11