Bernd Schröder

HEAVY METAL EXTRACTION WITH THIOCARBAMIC-O-ALKYLESTERS

ABSTRACT Two types of thiocarbamic-O-alkylesters, four bidentate ligands HL and one bis-bidentate ligand H2L, were used as extractants for heavy metal ions from aqueous solutions. Silver(I) was extracted as neutral complexes in a yield > 99 %. The underlying stoichiometry and the extraction constants are discussed. The extraction of silver&I) by the bis-bidentate ligand is significantly more effective than the extraction by the analogous bidentate compound. In a dioxane/water mixture neutral, cationic and anionic silver complexes were found by means of pAg and pH potentiometric titrations. The extraction behavior is discussed with regard to the calculated stability constants.

Protonation, complexation and thermochemical behaviour of N-benzoylthiocarbamic-O-alkylester anions in solution

Abstract Enthalpies of protonation and metal complex formation of anions of a series of five N -benzoylthiocarbamic- O -alkylesters (R=Et, i -Pr, n -Bu, n -Hex, n -Dodec; 1–5 ) have been measured by titration calorimetry. Using known stability constants the reaction entropies have been calculated. The free ligands HL are verified to react as NH-acids. The remarkable gain of entropy mainly depends on the high number of lost molecules from the extended solvation shell of the reacting species in the 1,4-dioxane/water mixture. The nickel(II) cations are bound in the complex through similar forces than the NH-proton in the ligand.

Synthesis, characterization and thermochemical properties of N-acyl-N′,N′-diethylthioureas

Three N-acyl-N′,N′-diethylthioureas, RCONHCSNEt2, R = niPr, iBu, tBu, have been prepared and characterised. The standard (po n= 0.1 MPa) molar enthalpies of combustion in oxygen of the three crystalline compounds, at T n= 298.15 K, have been measured by rotating bomb-combustion calorimetry, and the standard molar enthalpies of sublimation of the compounds by microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in their crystalline and gaseous phases, respectively. The derived standard molar enthalpies of formation in the gaseous state are discussed comparatively. Acid constants and some complex stabilities have been measured pH-potentiometrically in dioxane–water mixture. The crystal structure of N,N-diethyl-N′-isovaleroylthiourea is presented nand shows a delocalization of the π electrons of the CS group over the carbon–amine nitrogen bond, CS–NEt2, stabilising the molecule, in accordance with the thermochemical results.