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Synthesis, silver (I) extraction and silver (I) binding studies of novel N1,N3-bis(2-(benzylthio)ethyl)propanediamide derivatives


Solvent or liquid–liquid extraction represents a highly valuable technique for the selective recovery of metals from the aqueous phase due to the ease of operation and short turnaround times. Ligands bearing soft donor atoms including nitrogen and sulfur are ideal candidates for selective silver recovery due to their preference for silver binding. Herein, novel N1,N3-bis(2-(benzylthio)ethyl)propanediamide derivatives bearing sulfur and nitrogen donor atoms were prepared in low to high yields and tested for Ag+ extraction from ternary aqueous solutions also containing Cu2+ and Pb2+ following a well-established solvent extraction protocol. It was observed that electronics effects at the 4-aryl position in the propanediamide (or malondiamide) derivatives had a significant effect on the selectivity, but little effect on the efficiency of Ag+ extraction with the 4-methoxy analogue proving the most selective. Steric hindrance provided by dimethyl substitutions at the α-positions to the sulfur atoms had negative effects on Ag+ extraction efficiency and selectivity, while diethyl steric hindrance at the methylene center lowered selectivity but increased extraction efficiency for Ag+. Detailed binding studies reveal that one of the malondiamide derivatives which lacked the electronic and steric hindrance groups studied coordinated Ag+ in a 1:1 fashion suggesting a tetrahedral complex geometry. Overall, the results show that simple modification of the electronics and sterics of the N1,N3-bis(2-(benzylthio)ethyl)propanediamides, can improve their selectivity for Ag+ recovery from the aqueous phase.

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The authors would like to thank The Commonwealth Scholarship Commission in the United Kingdom and The University of Warwick for funding the research under grant number NGCS-2015-448.

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Conceptualization, experimental design, experimental work, first draft (ADA). Conceptualization, experimental design, paper review (AJC).

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Correspondence to Abiodun D. Aderibigbe.

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Aderibigbe, A.D., Clark, A.J. Synthesis, silver (I) extraction and silver (I) binding studies of novel N1,N3-bis(2-(benzylthio)ethyl)propanediamide derivatives. Chem. Pap. 75, 397–410 (2021).

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  • Malondiamide derivatives
  • Selective silver(I) extraction
  • Electronics
  • Sterics
  • Job plot
  • 1H NMR titration