Actinide-lanthanide separation (ALSEP) has been a topic of interest in recent years as it has been shown to selectively extract problematic metals from spent nuclear fuel. However, the process suffers from slow kinetics, prohibiting it from being applied to nuclear facilities. In an effort to improve the process, many fundamental studies have been performed, but the majority have only focused on the thermodynamics of separation. Therefore, to understand the mechanism behind the ALSEP process, molecular dynamics (MD) simulations were utilized to obtain the dynamics and solvation characteristics for an organic extractant, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEHEHP). Simulations were conducted with both pure and biphasic solvent systems to evaluate the complex solvent interactions within the ALSEP extraction method. The MD simulations revealed solvation and dynamical behaviors that are consistent with the experimentally observed chemical properties of HEHEHP for the pure solvent systems (e.g., hydrophobic/hydrophilic behaviors of the polar head group and alkyl chains and dimer formation between the ligands within an organic solvent). When present in a biphasic solvent system, interfacial behaviors of the ligand revealed that, at low concentrations, the alkyl side chains of HEHEHP were parallel to the interfacial plane. Upon increasing the concentration to 0.75 M, tendency for the parallel orientation decreased and a more perpendicular-like orientation was observed. Analysis of ligand solvation energies in different solvents through the thermodynamic integration method demonstrated favorability toward n-dodecane and biphasic solvents, which is in agreement with the previous experimental findings.
The stabilities of radicals play a central role in determining the thermodynamics and kinetics of many reactions in organic chemistry. In this data descriptor, we provide consistent and validated quantum chemical calculations for over 200,000 organic radical species and 40,000 associated closed-shell molecules containing C, H, N and O atoms. These data consist of optimized 3D geometries, enthalpies, Gibbs free energy, vibrational frequencies, Mulliken charges and spin densities calculated at the M06-2X/def2-TZVP level of theory, which was previously found to have a favorable trade-off between experimental accuracy and computational efficiency. We expect this data to be useful in the further development of machine learning techniques to predict reaction pathways, bond strengths, and other phenomena closely related to organic radical chemistry.
A systematic study of the behavior of different leaving groups on a variety of ester‐based monomers was performed for the chain‐growth polycondensation synthesis of poly(N‐octyl benzamide). Linear and branched alkane esters were compared with their phenyl analogs using both computational and experimental methods. Kinetic experiments along with qualitative solubility observations were used, with the aid of nuclear magnetic resonance spectroscopy and gel‐permeation chromatography, to determine progress of the reaction, molecular weights, and molecular weight distributions. It was found that the reactivity of the monomer's ester group depends more on the stability of the leaving alkoxide than the electrophilicity of the carbonyl carbon, which contradicts previous literature. The order of reactivity increases for the alkyl esters with decreasing steric hindrance and decreasing pKa of the substituent. For the phenyl ester derivatives, the more electron withdrawing character of a para substituent increases the reactivity of the ester group, due to the higher resonance stabilization of the leaving phenoxide anion, not due to an increase in the electrophilicity of the carbonyl carbon.
(HMF) is one of the important renewable platform
compounds that can be obtained from biomass feedstocks through glucose
conversion catalyzed by Brønsted and Lewis acids. However, it
is challenging to enhance the HMF yield due to side reactions. In
this study, a systematic approach combining theory and experiment
was performed to investigate the influence of Lewis acids and organic
solvents on the HMF yield. For the Lewis acid effect, a relationship
between chemical hardness and experimental HMF yields was found in
the rate-limiting step of glucose-to-fructose isomerization for six
metal chlorides; HMF production was promoted when the metal chloride
and a substrate had a similar chemical hardness. To study the organic
solvent effect, a multivariate model was developed based on the insights
gained from the mechanistic study of fructose dehydration, to predict
HMF yields in a given water-organic cosolvent system. It showed a
reliable accuracy in evaluating HMF yields with a mean absolute error
(MAE) of 3.0% with respect to experimental HMF yields for 13 solvents,
and also predicted HMF yields with a MAE of 10.7% for four new solvents.
Chemical interpretation of the model revealed that it is desirable
to use a solvent capable of stabilizing the carbocation intermediates
with low proton transfer activity and high hydrogen bond basicity,
to maximize the HMF yield. This multivariate model informs experimentalists
about rational selection of solvents with very low computational costs
needed to calculate only six variables for each solvent. It can be
expanded to other catalytic systems such as heterogeneous Brønsted–Lewis
bifunctional catalysts and enables optimization of reaction conditions
to obtain other useful platform molecules through biomass conversion.
We have determined the identity of the complexes extracted into the ALSEP process solvent from solutions of nitric acid. The ALSEP process is a new solvent extraction separation designed to separate americium and curium from trivalent lanthanides in irradiated nuclear fuel. ALSEP employs a mixture of two extractants, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (TEHDGA) in n-dodecane, which makes it difficult to ascertain the nature of the extracted metal complexes. It is often asserted that the weak acid extractant HEH [EHP] does not participate in the extracted complex under ALSEP extraction conditions (2−4 M HNO 3 ). However, the analysis of the Am extraction equilibria, Nd absorption spectra, and Eu fluorescence emission spectra of metal-loaded organic phases argues for the participation of HEH[EHP] in the extracted complex despite the high acidity of the aqueous phases. The extracted complex was determined to contain fully protonated molecules of HEH [EHP] with an overall stoichiometry of M(TEHDGA) 2 (HEH[EHP]) 2 •3NO 3 . Computations also demonstrate that replacing one TEHDGA molecule with one (HEH[EHP]) 2 dimer is likely energetically favorable compared to Eu(TEHDGA) 3 •3NO 3 , whether the HEH[EHP] dimer is monodentate or bidentate.
A detailed investigation into the role of initiator structure, the presence of an initiator, and basicity of the non‐nucleophilic base in the chain‐growth condensation (CGC) synthesis of poly(N‐octyl benzamide) was conducted. A series of phenyl ester dimethyl amide initiators with different leaving groups were synthesized and used in the CGC preparation of poly(N‐octyl benzamide). Additional polymerizations were conducted without the presence of an initiator and with different non‐nucleophilic bases. Kinetic studies, along with nuclear magnetic resonance spectroscopy and gel‐permeation chromatography, were used to determine progress of the reaction, molecular weights, and molecular weight distributions. The experimental and computational results demonstrated that initiators containing electron‐withdrawing substituent phenyl esters, such as the p‐nitrophenyl ester, and electron‐withdrawing carbonyl character on the parent benzoate produce polymers with controllable molecular weights and narrow molecular weight distributions. Whereas, initiating species that contain electron‐donating character on the benzoate backbone, such as dimethylamino and methyl ester groups, produce polymers that resemble the results from reactions involving no initiators at all, indicating poor polymerization control.
This study explored the fundamental chemical intricacies behind the interactions between metal catalysts and carbon supports with graphitic nitrogen defects. These interactions were probed by examining metal adsorption, specifically, the location of adsorption and the electronic structure of metal catalysts as the basis for the metal−support interactions (MSIs). A computational framework was developed, and a series of 12 transition metals was systematically studied over various graphene models with graphitic nitrogen defect(s). Different modeling approaches served to provide insights into previous MSI computational discrepancies, reviewing both truncated and periodic graphene models. The computational treatment affected the magnitudes of adsorption energies between the metals and support; however, metals generally followed the same trends in their MSI. It was found that the addition of the nitrogen dopant improved the MSI by promoting electronic rearrangement from the metals' d-to s-orbitals for greater orbital overlap with the carbon support, shown with increased favorable adsorption. Furthermore, the study observed periodic trends that were adept descriptors of the MSI fundamental chemistries.
scite is a Brooklyn-based startup that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.