Synthesis, Characterization And Extractive Behaviors Of Imide Extractants

Extractant is a key element in a solvent extraction process. In the past 30 years or so, studies on extractants have been mainly undertaken with two sorts of extractants: organophosphorus compounds and amide compounds. Many organophosphorus extractants have been used, but degradation products lead to the formation of precipitates or retention of actinides in the solvent. Moreover, the incineration of the spent solvent produces radioactive waste containing sulphur . A number of research groups have been investigating the extraction of f-block ions by amide ligands. Their chelating effect of monoamides and diamides allow the extraction of cations from concentrated nitric acid solutions. The fact that they contain no phosphorus atoms is important; the solvents are hence completely incinerable and do not generate any new waste. Their degradation products are accordingly less harmful to the process.We have been applying molecular mechanics to the design of ligands that selectively bind certain metal ions. The hypothesis underlying this approach is that differences in metal ion binding with multidentate ligands bearing the same number and type of donor groups are primarily attributable to intramolecular steric factors. The strain energy can be correlated with metal ion binding strength, thereby providing a method to screen a series of candidates and select the optimal architecture for a set of donor atoms.On the basis of the weightiness of extractants in the nuclear industry, the aim of this dissertation is about synthesizing extractants dialkylimides. We identified a dialkylimide architecture that is pre-organized for complexation and offers binding sites that are complementary for the actinides.The present paper presents a systematic research of the chemical properties of three new classes of extractants (i.e. dialkylimides, N-acetyl diethylimides and N-butyldiethylimides). Dialkylimides are synthesized starting from acyl -amide and acyl-chloride following one direct procedure in the presence of pyridine.N-Butyl diethylimide are alkylated through phase transfer catalysis of PolyEthylene Glycols. The procedure of N-acetyl diethylimides consists in treating a cooled, anhydrous methylene chloride of equivalent of acetyl chloride with slightly more than equivalent of triethylamine. Several dialkylimide extractants with the different backbones were synthesized and their extractability for uranium(VI) and thorium (IV) were measured and compared. Dialkylimide are optimum for the weak acid and neutral medium while N-acetyl diethylimide and N-butyl diethylimide for acid medium.The structure of the dialkylimide function group was found to strongly affect the separation behaviors of actinides in solvent extraction system. Alkyl chain length of the dialkylimide strongly affects the extractability of uranium and thorium.We found that the shorter the chain length is, the higher is the extractability. We also compare the extraction strength of straight-chain and branched-chain dialkylimide and find the latter to be very weak extractants under the neutral conditions that we employed. The dialkylimides is a kind of ion exchange extractants.The studies also show that N-acetyl diethylimide and N-butyl diethylimide do extract uranium and thorium from acid medium. Hitherto, effects of important parameters such as aqueous acidity, reagent concentration, temperature, etc, on the distribution ratio of uranium and thorium are experimentally studied. The thermodynamic parameters for the extraction reactions were evaluated by carrying the experiments at different temperatures and shaking times. The higher acidity leads to the weaker extractive ability for uranium or thorium. The higher temperature supports the extraction. The stoichiometry of the extracted complexes is 1:1. The N-butyl diethylimide and N-acetyl diethylimide belong to chelated extractants.Since we had recently prepared N-butyl diethylimide for studies on the extraction of uranium and thorium, we thought that it would be worthwhile to extend our investigations to include the...