Structure and reactivity of alkali metal enolates

The oxygen reduction reaction (ORR) on a polycrystalline Pt surface was studied using cyclic voltammetry techniques, and the influence of reaction media on the ORR is examined by comparing the ORR in NaOH and KOH solutions with concentration ranging from 0.5 to 14 M at 298 K. The results show that, in NaOH and KOH solutions, the ORR, a quasi-reversible diffusion-controlled reaction, is largely dependent on the electrolyte conditions, and KOH solutions are superior to NaOH solutions for the ORR process in both thermodynamic and kinetic consideration. As the alkaline concentration increases, the ORR performance frustrates, and the protonation of superoxide is suppressed; thus, the ORR shifts from a 2e reduction pathway to a 1e reduction pathway in both solutions.

Comparison of the oxygen reduction reaction between NaOH and KOH solutions on a Pt electrode: the electrolyte-dependent effect.

The enthalpies and entropies of complexation of alkali and alkaline-earth metal cations by several macrobicyclic ligands have been obtained from calorimetric measurements and from the previously determined stability constants [2]. Both enthalpy and entropy changes play an important role in the stability and selectivity of the complexes. Particularly noteworthy are the large enthalpies and the negative entropies of complexation obtained for the alkali cation complexes (Na+, K+, Rb+ and Cs+ cryptates). The Sr2+ and Ba2+ as well as [Li+ ⊂ 2.1.1]1 and [Na+ ⊂ 2.2.1] cryptates are of the enthalpy dominant type with also a favourable entropy change. The Ca2+ and [Li+ ⊂ 2.2.1] cryptates are entirely entropy stabilized with about zero heat of reaction. The high stability of the macrobicyclic complexes as compared to the macromonocylcic ones, the cryptate effect, is of enthalpic origin. The enthalpies of complexation display selectivity peaks, as do the stabilities, whereas the entropy changes do not. The high M2+/M+ selectivities found in terms of free energy, may be reversed when enthalpy is considered in view of the very different role played by the entropy term for M2+ and M+ cations. The enthalpies and entropies of ligation show that whereas the cryptate anions are similar in terms of entropy irrespective of which cation is included, the ligands, despite being more rigid than the hydration shell, are nevertheless able to adjust to some extent to the cation. This conclusion agrees with published X-rays data. The origin of the enthalpies and entropies of complexation is discussed in terms of structural features of the ligands and of solvation effects.

Enthalpy and Entropy of Formation of Alkali and Alkaline‐Earth Macrobicyclic Cryptate Complexes [1]

Die Entwicklung der Fourier-Transform-Technik hat die 23Na-NMR-Spektroskopie zu einem wichtigen Hilfsmittel werden lassen, mit dem der Organiker wie der Bio-Anorganiker Phanomene der Solvatation und der Ionenpaar-Bildung direkt beobachten kann. Die chemische Verschiebung und die Linienbreite von 23Na-Signalen erschliesen Komplexstabilitatskonstanten, Korrelationszeiten von Reorientierungsvorgangen und die Mikrodynamik in der Koordinationssphare des Natrium-Ions. In Konkurrenzexperimenten konnen mit der 23Na-NMR-Spektroskopie auch die Bindungsverhaltnisse weiterer Kationen studiert werden.

Kernresonanzspektroskopie mit Natrium-23

The available literature data concerning the kinetics and mechanism of the cyclotrimerisation and polycyclotrimerisation of isocyanates in the presence of catalysts of various kinds are presented and analysed in this review. Attention hes been concentrated on studies published during the last ten years. A number of features characterising the kinetics of the cyclotrimerisation of isocyanates have been deduced from the information about the process presented here. The mechanism of the reaction in the presence of basic catalysts is examined. The bibliography includes 263 references.

https://iopscience.iop.org/article/10.1070/RC1985v054n11ABEH003160/pdf

C. C. Chao

Papers

Solvent effects in organic chemistry. XIV. Complexing of sodium ion by various common solvents as ligands in acetone solutions

Loesungsmitteleffekte in der organischen chemie 14. mitt. komplexierung des natrium-ions durch loesungsmittel als liganden in acetonloesungen