The extraction behavior of zinc(II) and cadmium(II) complexes of
O,
O'-dialkyldithiophosphate(R
2dtp
-) with chloroform was investigated in a medium with constant ionic strength at 25°C. Four kinds of R
2dtp
- were examined,
i.
e., dimethyl(Me
2dtp
-), diethyl(Et
2dtp
-), dipropyl(Pr
2dtp
-) and dibutyl(Bu
2dtp
-) derivatives. The distribution ratio,
D, of metal ion was calculated from the extracted metal ion concentration which was determined by AAS after the oxidative decomposition of the extracted complex with an NH
4I-I
2 solution. The composition, overall formation constant(β
2), and distribution constant(
KD) of the complex extracted were determined by analyzing a logarithmic plot of
D vs. [R
2dtp
-] by a curve-fitting method. The species extracted was [M(R
2dtp)
2](M=Zn, Cd) in all cases. The values of
KD increased in the order Me
2dtp
-<Et
2dtp
-<Pr
2dtp
-≈Bu
2dtp
- and the values of β
2 increased in the order Me
2dtp
-<Et
2dtp
-<Pr
2dtp
-<Bu
2dtp
-.The cadmium complex was always more stable than the corresponding zinc complex.
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