Gamma-radiolytic stability of new methylated TODGA derivatives for minor actinide recycling

Abstract

The stability against gamma radiation of MeTODGA (methyl tetraoctyldiglycolamide) and Me2TODGA (dimethyl tetraoctyldiglycolamide), derivatives from the well-known extractant TODGA (N,N,N',N'-tetraoctyldiglycolamide), were studied and compared. Solutions of MeTODGA and Me2TODGA in alkane diluents were subjected to (60)Co γ-irradiation in the presence and absence of nitric acid and analyzed using LC-MS to determine their rates of radiolytic concentration decrease, as well as to identify radiolysis products. The results of product identification from three different laboratories are compared and found to be in good agreement. The diglycolamide (DGA) concentrations decreased exponentially with increasing absorbed dose. The MeTODGA degradation rate constants (dose constants) were uninfluenced by the presence of nitric acid, but the acid increased the rate of degradation for Me2TODGA. The degradation products formed by irradiation are also initially produced in greater amounts in acid-contacted solution, but products may also be degraded by continued radiolysis. The identified radiolysis products suggest that the weakest bonds are those in the diglycolamide center of these molecules.

Radiolytic and hydrolytic degradation of the hydrophilic diglycolamides

“…These have included studies of the radiation chemistry of tetraoctyldiglycolamide (TODGA) and tetra(2-ethylhexyl)diglycolamide (TEHDGA), [7] didodecyldioctyldiglycolamide (D 3 DODGA), [8] and methyl-tetraoctyldiglycolamide (Me-TODGA) and dimethyl-tetraoctyldiglycolamide (Me 2 -TODGA). [9] Unlike many other fuel cycle ligands, all the lipophilic DGAs in dodecane diluent were degraded by irradiation with about the same dose constant (kGy -1 ), and that rate did not vary significantly in the presence or absence of contact with aqueous phases of varying acidity. Common products of irradiation were trialkyldiglycolamides produced by loss of an alkane group from one of the N-atoms, production of carboxylic acids following C-N bond rupture with loss of the amine group, and acetamides and glycolamides resulting from rupture of the central ether linkage.…”

Testing a simple approach for theoretical evaluation of radiolysis products in extraction systems. A case of N,O-donor ligands for Am/Eu separation

“…The radiation-induced hydrolysis, as one of the main processes resulting in loss of the extraction ability upon irradiation, is also typical for aliphatic amides, such as malonamides 37 and diglycol amides. 5 Samples irradiated in the presence of nitric acid contained a variety of degradation products similar to the case of ageing, including substance IV that was established for 6 M nitric acid solution. In contrast to the samples that had no contact with nitric acid, there was no signicant amount of hydrolysis products, which evidences about hydrolysis suppression by nitric acid under gamma-irradiation.…”

“…Earlier, the radiolytic stability of a number of extraction systems developed for both the group separation of An(III)/Ln(III) and their individual element's separation has been studied in details. [3][4][5][6][7] The classical experimental approach for testing of the radiation stability is an external gamma irradiation of organic extractant solutions, subsequent extraction experiments and determination of qualitative and quantitative composition of radiolysis products. However only few studies were performed on the theoretical predictions of irradiation effects and the most radiation-stable ligands.…”

“…The second route is preferable for diluted (<0.1 M) extractants solutions. 5,10 In this case, products of radical addition and/or substitution in initial ligand should form. That is why the prediction of ligand radiation stability must be based on our knowledge about the position of reaction centers and "strength" of bonds in initial ligand to evaluate probability of radical reactions.…”

Preparation of Diglycolamides via Schotten–Baumann Approach and Direct Amidation of Esters

“…We found that an alkyl substituent at the backbone also has a considerable influence. 2,3 The extraction properties are considerably improved in case of tripodal DGAs 4 or when the DGA units are appended to a calix[4]arene skeleton. 5 Sasaki et al 6 prepared a series of DGAs with varying alkyl groups at the amidic nitrogen atoms by reaction of diglycolic anhydride with one equivalent of an amine.…”