THIO DERIVATIVES OF BETA DIKETONES AND THEIR METAL CHELATES .11. STABILITY CONSTANTS OF NICKEL(2), COPPER(2), ZINC(2), CADMIUM(2), AND LEAD(2) CHELATES OF 2 MONOTHIO-BETA-DIKETONES

The acid dissociation constant (pKD) of the monothio derivative of benzoyl-acetone, viz. 3-mercapto-1-phenylbut-2-en-1-one (I), was found to be 10·43 in 74·5 vol.% dioxan-water solution. Stoicheiometric stability constants (log kn) of five metal chelates of (I) and of the monothio derivative of dibenzoylmethane, viz. 3-mercapto-1,3- diphenylprop-2-en-1-one (II), have been measured in 74·5 vol.% dioxan- water solution with both chloride and perchlorate as supporting electrolyte. With chloride as supporting electrolyte the values obtained for log kav are as follows: with ligand (I), copper(II) 10·11, nickel(II) 9·25, zinc(II) 6·68, lead(II) 6·06, cadmium(II) 6·12; with ligand (II), copper(II) 10·66, nickel(II) 10·20, zinc(II) 7·44, lead(II) 7·11, cadmium(II) 6·90. With perchlorate as supporting electrolyte zinc, lead, and cadmium give values of log kav which are 1·5–1·9 units greater. The thermodynamic stability constants (logKn) were calculated from the stoicheiometric constants by use of the equations Log K1 = logk1 + 2·30 logK2 = log k2 + 1·15 For the copper and nickel complexes of both (1) and (II) log Kav is greater than pKD; such a situation has been reported in only a few instances. From the data obtained with chloride as a supporting medium, approximate stoicheiometric stability constants were calculated for the chloro complexes MCl+ (M = Zn, Cd, Pb) in 74·5 vol.% dioxan. The values obtained were: ZnCl+, 5·0; CdCl+, 5·7; PbCl+, 5·0. © 1969, CSIRO. All rights reserved.