TY - JOUR
T1 - Radiation stability of cations in ionic liquids. 3. Guanidinium cations
AU - Shkrob, Ilya A.
AU - Marin, Timothy W.
AU - Bell, Jason R.
AU - Luo, Huimin
AU - Dai, Sheng
PY - 2013/11/21
Y1 - 2013/11/21
N2 - Due to their superb structural versatility, guanidinium cations find increasing use as constituent ions in room temperature ionic liquids (ILs). This versatility allows fine-tuning of hydrophobicity, which is an important concern for the use of ILs as diluents for metal ion separations. However, the presence of six C-N bonds in such cations poses a question, whether the guanidinium based ILs can be considered as diluents for nuclear separations, given that the radiation emitted by the decaying radionuclides can break these relatively weak bonds over the use cycle of the solvent. As nothing is presently known about the radiolytic stability of the guanidinium cations, we addressed this question using 2-dialkylamino-1,3-dimethylimidazolidine based cations (R = Et, Pr, and Bu) as a representative model for the entire class of such cations, and assessed their stability in 2.5 MeV electron beam radiolysis. Electron paramagnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry have been used to establish chemical mechanisms for radiation damage in guanidinium cations. Our conclusion is that radiation stability of these cations is not significantly different from that of more familiar aliphatic and aromatic IL cations. In fact, these cations yield exceptionally stable radicals, and fragmentation occurs only in their radiolytically generated excited states. The predominant chemical pathway for the cation decomposition is the elimination of their aliphatic arms, with radiolytic yields of 0.65 to 1.06 to 1.46 per 100 eV from R = Et to R = Bu, respectively. The total loss of the parent cation was estimated as 2.62, 1.65, and 1.98 species per 100 eV. While this attrition is not negligible, it is comparable to other organic cations that have fewer fissile C-N bonds. Many of the products are either modified guanidinium ions or protonated bases that are not expected to interfere with radionuclide separations.
AB - Due to their superb structural versatility, guanidinium cations find increasing use as constituent ions in room temperature ionic liquids (ILs). This versatility allows fine-tuning of hydrophobicity, which is an important concern for the use of ILs as diluents for metal ion separations. However, the presence of six C-N bonds in such cations poses a question, whether the guanidinium based ILs can be considered as diluents for nuclear separations, given that the radiation emitted by the decaying radionuclides can break these relatively weak bonds over the use cycle of the solvent. As nothing is presently known about the radiolytic stability of the guanidinium cations, we addressed this question using 2-dialkylamino-1,3-dimethylimidazolidine based cations (R = Et, Pr, and Bu) as a representative model for the entire class of such cations, and assessed their stability in 2.5 MeV electron beam radiolysis. Electron paramagnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry have been used to establish chemical mechanisms for radiation damage in guanidinium cations. Our conclusion is that radiation stability of these cations is not significantly different from that of more familiar aliphatic and aromatic IL cations. In fact, these cations yield exceptionally stable radicals, and fragmentation occurs only in their radiolytically generated excited states. The predominant chemical pathway for the cation decomposition is the elimination of their aliphatic arms, with radiolytic yields of 0.65 to 1.06 to 1.46 per 100 eV from R = Et to R = Bu, respectively. The total loss of the parent cation was estimated as 2.62, 1.65, and 1.98 species per 100 eV. While this attrition is not negligible, it is comparable to other organic cations that have fewer fissile C-N bonds. Many of the products are either modified guanidinium ions or protonated bases that are not expected to interfere with radionuclide separations.
UR - http://www.scopus.com/inward/record.url?scp=84888629623&partnerID=8YFLogxK
U2 - 10.1021/jp408253y
DO - 10.1021/jp408253y
M3 - Article
AN - SCOPUS:84888629623
SN - 1520-6106
VL - 117
SP - 14400
EP - 14407
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 46
ER -