Search

Herein we report binary acid Sc(OTf)3/TfOH-catalyzed alkenylation of arenes with alkynes. In this system, the high-energy vinyl carbocations with activated and weakly coordinating trifluoromethanesulfonate anions by Lewis acid Sc(III) can undergo facile Friedel-Crafts reactions with arenes to give the desired adducts in up to 90% yield and with high Z-selectivity.

An unprecedented binary acid accelerated oxidative radical annulation of sulfonyl hydrazones with simple olefins is described. Notably, this method provides a novel oxidative radical cycloaddition for the construction of six-member heterocycles. It offers a rapid and efficient approach to tetrahydropyridazines which are key structural motifs in pharmaceutically active compounds.

We describe herein a viable binary acid strategy for the catalytic Nazarov reaction of aryl vinyl ketones. Simply combining a Lewis acid and a Brønsted acid led to a dramatic enhancement of the catalytic activity in the Nazarov reaction of aryl vinyl β-ketoesters. The obtained optimal binary acid catalyst In(OTf)(3)/diphenyl phosphoric acid (DPP) can be applied to a range of aryl vinyl ketones with good activity. A trend of reactivity has also been summarized on the basis of mapping of the substituents.

Pristine carbon nanotubes (CNTs) dissolve as polycarbocations in superacids through direct protonation. The solvating power of a superacid is determined by the stability of the conjugate base anion that competes with the CNTs for the dissociated proton. We have demonstrated that this equilibrium can be controlled in a predictable fashion, thus rendering the solvating power of a superacid system tunable. In this article, we show that the solvating power of chlorosulfonic acid can be changed in a desired fashion by forming binary mixtures in different proportions with a non-superacid such as methane sulfonic acid. Thus, the successive extraction of carbon nanotubes with binary acid mixtures of increasing solvating power leads to the differentiation of CNTs by their molecular geometry. We show that solvation by direct protonation is sensitive to the geometric strain at the carbon atom and, hence, to the nanotube diameter. In this respect, the direct protonation method is distinct from surfactant-based or electrical-field-based methods that distinguish metallic CNTs from semiconducting types mainly on the existence of finite density of states or not at the Fermi level. We have employed solid-state Raman spectroscopic analysis of the CNT radial breathing modes and UV-vis absorption spectroscopy and a systematic mapping method to support our conclusions. We believe the concept demonstrated in this paper holds the potential to be developed into a chemical tool kit useful in the scaleable separation of CNTs by their (n, m) types, thus paving the way for molecular carbon nanotechnology.

The Raman spectroscopy technique has been employed to probe, as a function of temperature, the ionic and molecular speciation within the aqueous phase for systems of potential relevance to stratospheric chemistry. The systems studied, over the temperature range 200−300 K, were (i) binary HNO3:H2O and H2SO4:H2O mixtures and (ii) ternary HNO3:H2SO4:H2O (NSW) mixtures. The contributions of the concentration coefficient, Qm, to the equilibrium dissociation constants were assessed from the spectroscopic data. It was observed that speciation within the binary acid systems shifts toward the ionized form as temperature and concentration decrease because of increasing proton stabilization. The ternary NSW acid displays some similar properties to the binary counterparts, though a dominance of SO42-aq over NO3-aq ions in the competition for protons is observed. This effect leads to the HSO4- ion becoming the principal associated acid form and its presence is found to determine the behavior of the NSW systems at all ...

This article deals with the rather complicated if not incorrect way that the strengths of binary acids are rationalized to students in many classrooms owing to the way it is presented in first-year chemistry textbooks. The common explanations, which use the homolytic bond dissociation energy as a rationalization of the trend in acid strengths when going down a group in the periodic table and the difference in electronegativity when going across a period, are contradictory and are replaced by one explanation for all binary acids. The present explanation uses a Born–Haber cycle involving homolyic bond dissociation energies, electron affinities, and ion solvation enthalpies to rationalize the trends observed in the acid strength of all binary acids whether going across a period or down a group in the periodic table, all which are concepts typically presented to students prior to the acidity concept.

Densites et viscosites a 308,15 K pour les systemes: acide propionique+aniline, +N-methylaniline et +N-ethylaniline

In the course of investigations of the reactions of diazo compounds with various types of acids, the authors have had occaaion to develop methods for analysis of mixtures of carboxylic acids by measurement of their reaction rates with diphenyldiazomethane. The carboxylic acid-diphenyldiazomethane reaction has obvious advantages for this purpose, as it is very convenient to follow spectrophotometrically (the diazo compound has a deep permanganatelike color), occurs in a wide range of solvents, and may be carried out with small amounts of materials. Furthermore, different carboxylic acids often show substantial differences in rate-for example, p-nitrobenzoic acid reacts approximately 25 times faster than p-aminobenzoic acid in ethyl alcohol at 30°. The principal disadvantages of the reaction for analytical purposes are the lack of simple stoichiometry in solvents like ethyl alcohol, where the reaction rate is strictly second-order, and nonintegral kinetic orders in carboxylic acid in aprotic solvents, where the reaction is quantitative. It is the purpose of the present paper to show how these disadvantages may be overcome in the analysis of binary acid mixtures.