Kinetics of the ligand substitution reactions of the copper(II) chelates of 1-(2-pyridylazo)-2-naphthol analogs with EDTA.
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概要
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The rates of the substitution reactions of copper(II) chelates of metallochromic indicators such as 1-(2-pyridylazo)-2-naphthol (PAN, Hpan), 1-(2-thiazolylazo)-2-naphthol (TAN, Htan), 2-(2-pyridylazo)-4-methylphenol (PAC, Hpac), 2-(2-thiazolylazo)-4-methylphenol (TAC, Htac), 4-(2-pyridylazo)resorsinol (PAR, H<SUB>2</SUB>par), and 4-(2-thiazolylazo)resorcinol (TAR, H<SUB>2</SUB>tar) were determined. The rate laws can be written as −\frac<I>d</I>[CuL]<I>dt</I>=<I>k</I><SUB>edta′</SUB><SUP>CuL</SUP> [CuL][edta′] for PAN, TAN, PAC, and TAC in the pH range of 4 to 6.5, and −\frac<I>d</I>[(CuL)′]<I>dt</I>=(<I>k</I><SUB>edta′</SUB><SUP>CuL</SUP>[CuL]+<I>k</I><SUB>edta′</SUB><SUP>CuHL</SUP>[CuHL])[edta′], where [(CuL)′]=[CuL]+[CuHL], for PAR and TAR in the pH range of 3.5 to 6.5. In the pH range lower than 3.5 the laws are written as −\frac<I>d</I>[CuL]<I>dt</I>=(<I>k</I><SUB>edta′</SUB><SUP>CuL</SUP>[edta′]+<I>k</I><SUB>H</SUB><SUP>CuL</SUP>[H])[CuL] for PAN, and as −\frac<I>d</I>[CuHL]<I>dt</I>=(<I>k</I><SUB>edta′</SUB><SUP>CuHL</SUP>[edta′]+<I>k</I><SUB>H</SUB><SUP>CuHL</SUP>[H])[CuHL] for PAR and TAR. The rate constants (μ=0.1, 25 °C, at dioxane 2 vol% or 5 vol% (PAN and TAN) (dm<SUP>3</SUP> mol<SUP>−1</SUP> s<SUP>−1</SUP>)) are <I>k</I><SUB>edta′</SUB><SUP>Cu(tan)</SUP>=2.8×10<SUP>4</SUP>, <I>k</I><SUB>edta′</SUB><SUP>Cu(pac)</SUP>=8.0×10<SUP>4</SUP>, <I>k</I><SUB>edta′</SUB><SUP>Cu(tac)</SUP>=4×10<SUP>6</SUP>, <I>k</I><SUB>edta′</SUB><SUP>Cu(par)</SUP>=2.0×10<SUP>3</SUP>, <I>k</I><SUB>edta′</SUB><SUP>Cu(tar)</SUP>=6.3×10<SUP>4</SUP>, <I>k</I><SUB>edta′</SUB><SUP>Cu(Hpar)</SUP>=1.2×10<SUP>4</SUP>, <I>k</I><SUB>edta′</SUB><SUP>Cu(Htar)</SUP>=7.9×10<SUP>5</SUP>, <I>k</I><SUB>H</SUB><SUP>Cu(pan)</SUP>=6.5×10, <I>k</I><SUB>H</SUB><SUP>Cu(Hpar)</SUP>=6.6×10<SUP>2</SUP>, and <I>k</I><SUB>H</SUB><SUP>Cu(Htar)</SUP>=1.2×10<SUP>4</SUP>. The rate constants, <I>k</I><SUB>edta′</SUB><SUP>CuL</SUP> are inversely proportional to the basicities of the donor atoms of indicators. Thus, the rate of color change of thiazolylazo compound is larger than that of corresponding pyridylazo compound in the chelatometry of copper(II).
- 公益社団法人 日本化学会の論文
著者
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Wada Hiroko
Laboratory Of Analytical Chemistry Nagoya Institute Of Technology
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Nakagawa Genkichi
Laboratory Of Analytical Chemistry Nagoya Institute Of Technology
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