Dithiodiglycolamide: novel ligand with highest selectivity and extractability for palladium R. Ruhela a,⇑ , J. N. Sharma a , B. S. Tomar b , M. S. Murali b , R. C. Hubli a , A. K. Suri a a Hydrometallurgy Section, Bhabha Atomic Research Centre, Mumbai 400 085, India b Radiochemistry Divison, Bhabha Atomic Research Centre, Mumbai 400 085, India article info Article history: Received 13 April 2011 Revised 16 May 2011 Accepted 22 May 2011 Available online 30 May 2011 Keywords: DTDGA Palladium HLW Distribution ratio Separation factor abstract A novel multidentate ligand N,N,N 0 ,N 0 -tetra(2-ethylhexyl) dithiodiglycolamide DTDGA has been synthe- sized and studied for its extraction behavior towards various elements present in high level liquid waste (HLW). The extractant showed remarkable extractability and selectivity for palladium vis a vis other metal ions present in HLW. The distribution ratio as well as the separation factor for palladium was found to be the highest reported so far thus making this extractant one of the most promising candidates for effective separation of palladium from HLW. Ó 2011 Elsevier Ltd. All rights reserved. Separation and recovery of palladium from high level liquid waste (HLW) solutions originating from PUREX process of spent nuclear fuel is necessary from the viewpoint of various problems encountered during vitrification 1 as well as the conceptualization of the process where HLW can be treated as a secondary source of these valuable metals. 2 For this purpose various ligands namely, tertiary and quaternary amines (tri-n-octylamine, tri-n-octylme- thylammonium chloride (TOMAC) and tri-n-octylmethylammoni- um nitrate (TOMAN)), 3 a-benzoinoxime (ABO), 4 dihexyl and dioctyl sulfides (DHS 5 and DOS 6 ), dihexyl disulfide (DHDS), 5 dioctyl and bis-(2-ethylhexyl) sulfoxides (DOSO 7 and BESO), 6 triisobutyl- phosphinesulfide (TIPS) 7 and benzoylmethylene triphenylphos- phorane (BMTTP), 8 have been developed during the last two decades. However, these ligands suffer from various limitations such as slow kinetics, 5,7,8 poor decontamination factor, 4,6 pH sensi- tivity, 3 solubility 3,4,7,8 and instability in acidic medium. 5,6 To over- come these problems there is a need for development of newer ligands with improved extraction efficiency as well as selectivity. In a recent work, we have reported the synthesis of novel ‘S’ do- nor ligand namely N,N,N 0 ,N 0 -tetra (2-ethylhexyl) thiodiglycolamide (T(2EH)TDGA) 9 and its remarkable selectivity for palladium extrac- tion vis a vis other metal ions present in HLW. High selectivity and extractability of the ligand was attributed to the presence of thio- etheric sulfur and amidic moiety appropriately placed in the ligand to chelate through more than one donor sites. 9 However, there are various aqueous streams where the concentration of palladium is in sub ppm levels for which an even more efficient extractant is re- quired along with high selectivity. To seek an even more efficient ligand for the said purpose, another novel class of ligand namely, dithiodiglycolamide, has been explored by us. It was envisaged that judicial incorporation of one more sulfur atom would result in more chelation thereby increasing the overall extractability thus increasing the ligand economy while retaining the selectivity. We now report the synthesis of a novel ligand namely, N,N,N 0 ,N 0 - tetra(2-ethylhexyl) dithiodiglycolamide (DTDGA) (Fig. 1) and demonstrate its superiority over previously reported ligands in palladium extraction from HLW. DTDGA was synthesized (Fig. 2) from commercially available and tailor-made materials. 10 All other chemicals used in this study were of reagent grade. The extraction study of metal ions was car- ried out at 25 ± 1 °C. 11 To establish the nature of extracted species, both the chemical (mole ratio method) as well as physical (ESI-MS) approaches were 0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2011.05.099 ⇑ Corresponding author. Tel.: +91 2225592959/621. E-mail address: riteshr@barc.gov.in (R. Ruhela). Figure 1. N,N,N 0 ,N 0 -Tetra (2-ethylhexyl) dithiodiglycolamides (DTDGA). Tetrahedron Letters 52 (2011) 3929–3932 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet