O-(2-Thiazolylazo)-4-Chlorophenol Complexes and Their Utility as Metallo-Chromic Indicators for Nickel(II) Ion

Abstract

The stability constants of the complexes formed between o-(2-thiazoiylazo)-4-chlorophenol (TACL) and bivalent metal ions obtained spectrophotometrically were: logK_MnR = 2.86, logK_CoR = 5.37, logK_NiR = 6.12, logK_{NiR 2} = 5.44, logK_CuR = 8.39, logK_ZnR = 4.54, logK_{ZnR 2} = 4.43 and logK_CuR = 5.65, (20°c, μ = 0.1, 10% v/v aqueous dioxane). These values coincided well with the Irving-Williams order.

The acid dissociation constants of analogous new dyestuffs synthesized in our Laboratory, o-(2-thiazolylazo)-phenol, o-(2-thiazolylazo)-4-bromophenol and o-(2-thiazoly-lazo)-4- iodophenol were 7.36, 7.35, and 7.25, respectively (20°C, μ = 0.1, 10% v/v aqueous dioxane).

TACL was found to be applicable as a metallochromic indicator for the titration of nickel(II) in weakly acidic media using EDTA as a titrant. No heating was required.