1967 Volume 40 Issue 9 Pages 2085-2089
o-, m-, and p-Nitrophenyl-azo-chromotropic acids were prepared as colorimetric reagents for thorium. The acid dissociation constants of the reagents have been determined spectrophotometrically, their pK1 values being 8.96, 8.60, and 8.77 for the and o-, m-, and p-compounds respectively at 25°C and when μ=0.1. The reagents form violet 1 : 1 complexes in an acidic solution. The apparent stability constants have been measured spectrophotometrically. The order of the apparent stability constants of the complexes agrees with that of the first acid dissociation constants of the reagents; m-nitro>p-nitro>o-nitro compounds.
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