Effective extraction of Pt(IV) as [PtCl6]2- from hydrochloric acid using a simple urea extractant

The conveniently prepared N,N'-dialkylsubstituted urea derivative, 1-butyl-3-(2-ethylhexyl)urea (L), was prepared and elucidated with respect to its performance as an extractant for [PtCl6](2-) from HCl solutions. L effectively extracts Pt(IV) and Pd(II) from 0.01 to 10 M HCl solutions with a high selectively over metal ions (Rh (III), Ir(III), Fe(III), Cu(II), Ni(II), Co(II), Zn(II), and Pb(II)) in the concentration range from 0.3 to 1.0 M HCl solutions. According to a slope analysis, the extraction equilibrium reaction of Pt(IV) by L was determined to be [PtCl6](aq.)(2-) + 2L(org.) + 2HCl(aq.) <-> (PtCl62-)center dot(HL+)(2org.) + 2Cl(aq.)(-), which is a typical ion-pair reaction. Ultraviolet-visible measurements proved that Pt(IV) was extracted into the organic phase by L as a [PtCl6](2-) salt. 195Pt nuclear magnetic resonance (NMR) investigation suggests that the Pt(IV) extracted by L has slightly lower electron density on the Pt(IV) ion compared with the Pt(IV) species extracted by the conventional extractant tri-n-octylamine from HCl solution. Infrared and H-1 NMR spectroscopic measurements revealed a strong hydrogen bonding between the Cl- ligands of [PtCl6](2-) and the N-H protons of L in the organic phase. Analysis of the water content in the organic phase, before and after the [PtCl6](2-) extraction, shows that 0.9-2.6 water molecules are released from the organic phase as the result of [PtCl6](2-) extraction from the aqueous into the organic phase by L.

Automated summary

A new extractant, 1-butyl-3-(2-ethylhexyl)urea (L), was studied for its efficient extraction of [PtCl6](2-) from HCl solutions, showing high selectivity and revealing the mechanism of extraction and changes in water content after extraction.