[Applications analytiques des oxocarbones-I: composition et constantes de stabilite des complexes molybdiques de l'ion bromanilate: dosage spectrophotometrique du molybdene(VI)].
The bromanilate ion B(2-) is a cyclic aromatic anion related to oxocarbons. We have shown by ultraviolet-visible spectrophotometry that it forms two 1:1 complexes with molybdenum(VI) in aqueous solution at pH 6. The variation of the conditional stability constants with acidity allows the calculation of the number of protons involved in each equilibrium. The formulae of the two complexes differ by a proton. The pK is 2.30. Molybdenum(VI) can be determined with bromanilic acid, H(2)B, at 340 nm in 3 or 1.4M perchloric acid. The accuracy is better than with chloranilic acid, H(2)C, when the concentration is about 1 mg/l. The better results obtained with H(2)B at high acidities are accounted for by the difference between the pK(1) values of the two acids (0.22 for H(2)B and 0.45 for H(2)C).
Poirier
J M
JM
Laboratoire de Chimie Analytique, Université René Descartes, 4, avenue de l'Observatoire, 75006 Paris, France.
Verchere
J F
JF