Intermolecular Interactions between Molecules in Various Conformational States: The Dimer of Oxalic Acid

I. O, R. E. E. Comparisons of the effects of solute interactions on partition coefficient, k D, in selected binary immiscible solvents: a case of oxalic acid and succinic acid

Background: The molecular distributions of solutes in binary immiscible solvents as used in partition coefficient technique serve as measures of the solute separation, concentration and beneficiation from contaminants. Methods: The effects of solute interactions on partition coefficient, k D, in selected binary immiscible solvents were investigated at 30 0C and atmospheric pressure. The activities from the interactions with changes of concentrations within the solvents were analysed. These were done using simple titration method. The solutes were distributed in the binary solvents and the concentrations from the two layers formed were determined by titration method. The interactions of oxalic acid and succinic acid in carbon tetrachloride-water, diethyl ether-water, and n-hexane-water were studied for the partition coefficient values in the respective systems, to determine the nature and degree of the interfering reactions that are affecting the distributions, and to ascertain the best binary solvents from the three systems. Results: Oxalic acid has the partition coefficient of 0.0738 in carbon tetrachloride-water with the dimerization constant of -15.7092 and ionization constant of 0.0303. Oxalic acid has the distribution coefficient of 0.0173, dimerization constant of 144.0167 and the ionization constant of 0.0035 in diethyl ether-water. Oxalic acid has the partition coefficient of 0.0279, dimerization constant of 20.2798 and ionization constant of 0.0019 in n-hexane-water. Succinic acid has the partition coefficient of -0.05617, dimerization constant of -18.5655 and ionization constant of 0.0284 in carbon tetrachloride-water. In diethyl ether-water, succinic acid has the partition coefficient of 0.0427, dimerization constant of -18.1611 and ionization constant of 0.0332. In n-hexane-water, succinic acid has the partition coefficient of -0.04274, dimerization constant of 71.9491 and ionization constant of 0.0265. Conclusion: From these results, carbon tetrachloride-water is recommended for the purification and extraction of oxalic acid from contaminants. Carbon tetrachloride-water is also the best binary immiscible solvent for succinic acid.

Additive-free hydrothermal leaching method with low environmental burden for screening of strontium in soil

In this work, hydrothermal leaching was applied to simulated soils (clay minerals vermiculite, montmorillonite, and kaolinite) and actual soils (Terunuma, Japan) to generate organic acids with the objective to develop an additive-free screening method for determination of Sr in soil. Stable strontium (SrCl₂) was adsorbed onto soils for the study, and ten organic acids (citric, L(+)-tartaric, succinic, oxalic, pyruvic, formic, glycolic, lactic, acetic, and propionic) were evaluated for leaching Sr from simulated soils under hydrothermal conditions (120 °C to 200 °C) at concentrations up to 0.3 M. For strontium-adsorbed vermiculite (Sr-V), 0.1 M citric acid was found to be effective for leaching Sr at 150 °C and 1 h treatment time. Based on these results, the formation of organic acids from organic matter in Terunuma soil was studied. Hydrothermal treatment of Terunuma soil produced a maximum amount of organic acids at 200 °C and 0.5 h reaction time. To confirm the possibility for leaching of Sr from Terunuma soil, strontium-adsorbed Terunuma soil (Sr-S) was studied. For Sr-S, hydrothermal treatment at 200 °C for 0.5 h reaction time allowed 40% of the Sr to be leached at room temperature, thus demonstrating an additive-free method for screening of Sr in soil. The additive-free hydrothermal leaching method avoids calcination of solids in the first step of chemical analysis and has application to both routine monitoring of metals in soils and to emergency situations.

Order-disorder phase transition in an anhydrous pyrazole-based proton conductor: the enhancement of electrical transport properties

The crystal structure of 1H-pyrazol-2-ium hydrogen oxalate has been studied at 100 K. It consists of two-dimensional layers built with one-dimensional chains that contain pyrazolium and oxalate acids bonded by N-HO and O-HO hydrogen bonds. According to the X-ray data and the Quantum Theory of Atoms in Molecules, it was shown that weak and moderate hydrogen bonds are present in the crystal at room temperature. The thermal stability was studied with the DSC, TGA, and DTG methods: three endothermic peaks are observed at 384, 420, and 469 K. Conductivity measurements have been performed in the temperature range from 300 to 433 K. At 383 K the pyrazole-oxalic acid framework loses its rigidity and the crystal undergoes an ordered-disordered phase transition. At this temperature, the value of the activation energy of proton conductivity changes from 1.14 to 2.31 eV. The proton conduction pathways and the transport mechanism have been studied with theoretical methods.

Assigning a structural motif using spontaneous molecular dipole orientation in thin films

Guided by the spontelectric behaviour of thin films of cis-methyl formate, infrared observations and computational investigations reveal the dimer structural motif of the crystalline solid.

Non-linear and non-local behaviour in spontaneously electrical solids

We show that solids displaying spontaneous dipole orientation possess quite general non-local and non-linear characteristics expressed through their internal electric fields.

Electrophilicity of oxalic acid monomer is enhanced in the dimer by intermolecular proton transfer

We have analyzed the effect of excess electron attachment on the network of hydrogen bonds in the oxalic acid dimer (OA)₂. The most stable anionic structures may be viewed as complexes of a neutral hydrogenated moiety HOA˙ coordinated to an anionic deprotonated moiety (OA-H)^-. HOA˙ acts as a double proton donor and (OA-H)^- as a double proton acceptor. Thus the excess electron attachment drives intermolecular proton transfer. We have identified several cyclic hydrogen bonded structures of (OA)₂^-. Their stability has been analyzed in terms of the stability of the involved conformers, the energetic penalty for deformation of these conformers to the geometry of the dimer, and the two-body interaction energy between the deformed HOA˙ and (OA-H)^-. There are at least seven isomers of (OA)₂^- with stabilization energies in the range of 1.26-1.39 eV. These energies are dominated by attractive two-body interaction energies. The anions are vertically bound electronically by 3.0-3.4 eV and adiabatically bound by at least 1.6 eV. The computational predictions are consistent with the anion photoelectron spectrum of (OA)₂^-. The spectrum consists of a broad feature, with an onset of 2.5 eV and spanning to 4.3 eV. The electron vertical detachment energy (VDE) is assigned to be 3.3 eV.

Isoreticular zirconium-based metal–organic frameworks: discovering mechanical trends and elastic anomalies controlling chemical structure stability

Understanding the mechanical properties of MOFs is crucial not only to yield robust practical applications, but also to advance fundamental research underpinning flexibility of a myriad of open-framework compounds.