SPECTROPHOTOMETRIC INVESTIGATIONS ON THE IRON (III)-MORELLIN COMPLEX
Abstract
1. Spectrophotometric investigations have been carried out on solutions of ferric chloride and iron (III)-morellin complex in an absolute alcohol medium.
2. It is noticed that there is a continuous shift in the absorption maximum of ferric chloride from 410 mu, to 490 mu as the concentration is raised from 2 .24 x 10 -4 M to 2.30x 10-1 M of ferric chloride in alcohol.
3. When ferric chloride is mixed with morellin. only one complex,having the molar composition Fe2R3 (R = morellin constituent) with an absorption maximum at 550 mil, is formed. The advantage of the complex formation can be taken to estimate iron (III) in the range 0.5 to 19 p.p.m.
4. The iron (III)-morellin complex dissociates in the absolute alcohol medium and the equilibrium constant K determined spectrophotometrically averages 495 x 10-17 at 25° C. The free energy of formation of the complex is — 22.15 Kcal./mole.
Morellin,1 an orange-yellow plant pigment. is isolated from the pericarp of the seeds of a tree, Garcinia morello. The molecule 2 of morellin contains the chelating group C, C, C-0, OH 3 which can form with metals inner complexes, having characteristic spiran-type structure. While studying the influence of foreign ions on the estimation of thorium and uranium with morellin, Rao and Patel observed that the ferric iron interfered in all proportions. The present authors have studied the behaviour of ferric iron on morellin and noticed the production of a greenish-black complex in aqueous alcoholic medium. It was found that the complex got ydrolysed in this medium on keeping. The investigation on the complex had, therefore, to be conducted in absolute alcohol medium. The colour formation with morellin in absolute alcohol is almost instantaneous. The maximum intensity of the colour is attained within a few minutes. The colour does not diminish even on keeping the solution for several days in the dark. The complex is found to be s table in alcohol but is destroyed in acid or alkaline alcoholic solutions. The present investigation was undertaken with a view to determining the composition of the complex foimed between ferric iron and morellin in alcohol medium. The molar composition of the iron-rnorellin complex has been determined by the Job's method of continuous variation s and verified by the slope ratio methods The molar ratio method' could not be used for the same purpose, since the complex suffered dissociation in solution, as is evident from the plots in Fig. 3. This method was, however, employed to determine the equilibrium constant and the free energy of formation of the iron-morellin complex.
2. It is noticed that there is a continuous shift in the absorption maximum of ferric chloride from 410 mu, to 490 mu as the concentration is raised from 2 .24 x 10 -4 M to 2.30x 10-1 M of ferric chloride in alcohol.
3. When ferric chloride is mixed with morellin. only one complex,having the molar composition Fe2R3 (R = morellin constituent) with an absorption maximum at 550 mil, is formed. The advantage of the complex formation can be taken to estimate iron (III) in the range 0.5 to 19 p.p.m.
4. The iron (III)-morellin complex dissociates in the absolute alcohol medium and the equilibrium constant K determined spectrophotometrically averages 495 x 10-17 at 25° C. The free energy of formation of the complex is — 22.15 Kcal./mole.
Morellin,1 an orange-yellow plant pigment. is isolated from the pericarp of the seeds of a tree, Garcinia morello. The molecule 2 of morellin contains the chelating group C, C, C-0, OH 3 which can form with metals inner complexes, having characteristic spiran-type structure. While studying the influence of foreign ions on the estimation of thorium and uranium with morellin, Rao and Patel observed that the ferric iron interfered in all proportions. The present authors have studied the behaviour of ferric iron on morellin and noticed the production of a greenish-black complex in aqueous alcoholic medium. It was found that the complex got ydrolysed in this medium on keeping. The investigation on the complex had, therefore, to be conducted in absolute alcohol medium. The colour formation with morellin in absolute alcohol is almost instantaneous. The maximum intensity of the colour is attained within a few minutes. The colour does not diminish even on keeping the solution for several days in the dark. The complex is found to be s table in alcohol but is destroyed in acid or alkaline alcoholic solutions. The present investigation was undertaken with a view to determining the composition of the complex foimed between ferric iron and morellin in alcohol medium. The molar composition of the iron-rnorellin complex has been determined by the Job's method of continuous variation s and verified by the slope ratio methods The molar ratio method' could not be used for the same purpose, since the complex suffered dissociation in solution, as is evident from the plots in Fig. 3. This method was, however, employed to determine the equilibrium constant and the free energy of formation of the iron-morellin complex.
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