Functional Group Transformation of Succindiamodoxime in Presence of Cu(Ⅱ)/Ni(Ⅱ)/U(Ⅵ)

Amidoxime-functionalized polymers are currently the most promising adsorbents for uranium extraction from seawater. The studies on the types of surface functional groups and related chemical reactions of such adsorbents can provide valuable information and guidance for their performance improvement and application research at molecular level. In this work, a small molecular ligand, succinamidedioxime (H2L), was used as the watersoluble surrogate of the open chain diamidoxime group on the surface of the adsorbents according to the processes of the preparation of the adsorbents, uranium adsorption, uranium elution and material regeneration. The functional group transformation reaction of H2L in heating condition, acidic solution, alkaline solution and in the presence of Cu(Ⅱ)/Ni(Ⅱ)/U(Ⅵ) was investigated respectively by 1H NMR spectrum, singlecrystal Xray diffraction and absorption spectrophotometry. The results show that H2L can undergo functional group transformation reactions under different conditions. The evolution of the 1H NMR spectrum of H2L with time in DMF-d7 at high temperature shows that H2L would be completely cyclized into succinimidedioxime (H3ⅠL) at 130 ℃ after 13 hours. In acidic solution (about 1 mol/L DCl), H2L would be first converted into Nhydroxysuccinimde (HⅡL) and then completely hydrolyzed into succinic acid. In contrast, H2L is relatively stable in alkaline solution, and will not react completely in 1 mol/L NaOD within three months. Three new complex crystals were successfully grown from the mixed solutions of H2L and Cu(Ⅱ)/Ni(Ⅱ) under different conditions and their structures were determined by singlecrystal Xray diffractometry. The absorption spectrum and compositional analysis of the complex precipitate of H2LU(Ⅵ) were performed. The determination of the structure and composition of the complexes also shows that H2L undergoes different functional structural transformations under different metal ions and acidbase conditions. In the presence of Cu(Ⅱ) and Ni(Ⅱ), the H2L functional group could be converted from diamidoxime to the structure of 2,5-diiminopyrrolidin-1-ol or 1-hydroxy-5-iminopyrrolidin-2-one. In the presence of U(Ⅵ), the H2L functional group could be converted into succinimidedioxime structure under heating conditions. In addition, the possible reaction pathways and mechanisms of the abovementioned functional group transformation reactions of H2L in the presence of Cu(Ⅱ)/Ni(Ⅱ)/U(Ⅵ) are proposed and discussed. These results provide a better understanding of the chemical reactions of the functional groups and an innovative approach to convert diamidoxime functional groups into imide dioxime functional groups which have higher uraniumbinding ability.