关键词: 反应机理, 卤化物, 稀土族, 显色剂, 稳定常数, 稀土金属络合物, 偶氮胂, 偶氮化合物, 萘二磺酸 P, 萘二酚 P

Complex formation between rare earth ions and polyhalogenated bisazo chromotropic acid was studied. The dissociation constants of tribromoarsenazo determine by spectrophotometric and potentiometric methods are pK1 = 0.8, pK2 = 1.7, pK3 = 2.5, pK4 = 6.5, pK5 = 9.6, and pK6 = 10.3, resp. These dissociation constants are larger than those of Arsenazo III and the stability constants of the complexes formed are higher than those for other reagents of the same type (log KS = 52 ?0.4). The molar ratio Ce/DBC-Arsenazo in the complex is estimated to be 1:3 by the Jobs continuous variation and the equilibrium shift methods. When halogen atom are introduced into the ligand, red- or blue-shifts of the absorption peaks occur. The shape of the absorption spectrum changes from asym. to sym. with decreasing electronegativity of the halogen atom.

Key words: REACTION MECHANISM, HALIDE, RARE EARTH SERIES, COLOUR REAGENTS, STABILITY CONSTANT, RARE EARTH METAL COMPLEX, ARSENAZO, AZO COMPOUNDS, NAPHTHALENEDISULFONIC ACID P, NAPHTHALENEDIOL P