The Reaction between Mercury(II) and Organic Compounds. VII. The Formation Constant and Analytical Application of the o-(2-Thiazolylazo)-4-chlorophenol-Mercury(II) Complex

The formation constants of the complex formed between o-(2-thiazolylazo)-4-chlorophenol TACL, and mercury(II) in 2% v/v dioxane-water were logKHgR+=6.21 and logKHgR2=6.10 at μ=0.1 and at room temperature. TACL was suggested as a suitable metallochromic indicator for the direct titrimetric determination of mercury(II) ions at pH 6.7–8.7 with an EDTA titrant. This optimum pH range was rather wide compared with that of the other metallochromic indicators, such as Cu-PAN, XO, and MTB. There were marked colour changes from deep blue to reddish-yellow or to violet at equivalence points. The mercury(II) ions up to 210 mg in 100 ml can be determined within an error of ±0.3% by this method.