Palladium(II) and N,N′-dimethyl-N,N′-dicyclohexylthiodiglycolamide – The extracted species from concentrated chloride solutions

• Pd(II) extraction reactions from HCl until 4.5 M by DMDCHTDGA in toluene are proposed.
• Distribution, spectroscopic and apparent molar volume data were collected.
• Inner-sphere complexes [PdCl2·L2] (L = DMDCHTDGA) accompanied by [LH+Cl−] should form.
• The existence of [LH]+[PdCl3L]− species could not be ruled out definitively.

The present article focuses on the systematic investigation of the palladium(II) extraction reactions from concentrated chloride media by N,N′-dimethyl-N,N′-dicyclohexylthiodiglycolamide (DMDCHTDGA) in toluene, relying both on equilibrium and spectroscopic data. The equilibrium results collected have been cautiously assessed by the analysis of the effects caused by the variation of the extractant, hydrogen and chloride ions concentrations on the Pd(II) distribution ratio. UV–visible, 1H nuclear magnetic resonance (NMR), Fourier-transform far infrared (FIR) and Raman spectroscopic results contributed for the clarification of the Pd(II) extraction reactions by DMDCHTDGA as well. The overall information suggests that inner-sphere complexes [PdCl2·L2] (L = DMDCHTDGA) should form, with the likely co-extraction of HCl traces. The determination of the apparent molar volumes indicates that DMDCHTDGA is essentially monomeric in toluene in the concentration range tested.