TRANS-EFFECT IN EXTRACTION KINETICS: PALLADIUM EXTRACTION BY 7-(1-VINYL-3,3,5,5-TETRAMETHYLHEXYL)-8-QUINOLINOL

Abstract

The rate of palladium extraction from chloride solutions by 7-(1-vinyl)-3,3,5,5-tetramethylhexyl)-8-quinolinol (KELEX 100) increased more than six hundred times when as little as 2 × 10⁻⁴M thiocyanate was added to the aqueous solution. Similar but smaller effects were produced by iodide and bromide. The influence of pH and the concentration of thiocyanate and ligand on the extraction rate indicated that the homogeneous chemical reaction of the type: is the rate determining step. The enhancement in the extraction rate parallels the size of the “trans-effect”, which decreases in the order of SCN¯> I¯>Br¯, in easing the replacement of a coordinated chloride ion by KELEX 100.