Cadmium and zinc 8-hydroxyquinolates precipitated from homogeneous solution and by the conventional method
1973 Volume 22 Issue 3 Pages 291-301
Details
1973 Volume 22 Issue 3 Pages 291-301
Cadmium and zinc 8-hydroxyquinolates precipitate quantitatively in the range of pH above 5.4 and 4.58 respectively and they are determined as Me(C9H6-NO)2 by drying at 130°C. These compounds were prepared as pure and easily filterable precipitates by the precipitation from homogeneous solution using 8-acetoxyquinoline. The quantitative treatment of cadmium 8-hydroxyquinolate precipitated from homogeneous solution, the solubilities and the properties of the crystals of cadmium and zinc 8-hydroxyquinolates are discussed in this paper.
An aqueous solution of 200 ml containing 1 to 30 mg of cadmium was added by 8-acetoxyquinoline solution in acetone at pH 7 to 9 and the solution was kept over night at room temperature. The precipitate was filtered and weighed after drying at 130°C for the gravimetric determination.
The concentration of saturated solution of cadmium and zinc 8-hydroxyquinolates in the pure water and in various buffer solutions was measured by the atomic absorption method and the results are shown in Table IV. The solubility products of cadmium and zinc 8-hydroxyquinolates were calculated as 10-26.24 and 10-27.68, respectively. The solubility curves of various species of 8-hydroxyquinolate (e. g. [Cd2+], [CdQ+], [CdQ2]) at various pHs and at various concentrations of 8-hydroxyquinoline are shown in Fig. 1 to 3.
The induction periods for the precipitation at various initial concentrations were measured and the crystalline nuclei of the precipitates of cadmium and zinc 8-hydroxyquinolates were recognized to be composed of 4 molecules by applying equations 16 and 17.
The crystal structure of zinc 8-hydroxyquinolate was analyzed by Merritt etc. and it belonged to the monoclinic system. The each particle of this precipitate was long hexagonal lamella and the long and short axes were b- and c-axes and a-axis was perpendicular to the lamellar crystal as shown in Fig. 6 and 7.
Cadmium 8-hydroxyquinolate precipitated from homogeneous solution has the dimorphism. It deposited as the precipitate containing long hexagonal lamellar crystals in the acidic medium, but in the basic medium it deposited as the precipitate composed of needle crystals at first and these needle crystals changed gradually to long hexagonal lamellar crystals in the mother liquor as shown in Fig. 8 and 9. It seems that the transformation occurred by the dissolution of the needle crystals and the deposition as the stable hexagonal crystals as shown in Fig. 10. The crystal structure of these crystals were analyzed. The needle crystal belonged to the tetragonal system whose lattice constants were such as a0=b0=10.3 and c0= 13.9 and the long axis was c-axis as shown in Fig. 11. The long hexagonal lamellar crystal belonged to the monoclinic system whose lattice constants were such as a0= 13.74, b0= 5.28, c0=11.36 and β=116°18'. This crystal was the isomorphous with zinc 8-hydroxyquinolate as shown in Fig. 12.
