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Herein, we disclosed an efficient protocol for the construction of chiral 3-allyl-3-hydroxyoxindoles via the enantioselective allylation reaction of isatins and allylboronates catalyzed by a simple binary acid Bi(OAc)3/CPA system under mild conditions. The synthetic utility of this strategy has been demonstrated through the formal synthesis of ent-CPC-1.

The increasing need for sustainable processes stimulates the production and recovery of renewable organic acids. The purification of these acids is often difficult because of similar acid volatilities but can be improved through extractive distillation. Generic insights into solvent effects on the separation efficiency for close-boiling acids are however lacking. This study provides insights into the effect of acidity, the acidity difference between the acids, the hydrogen-bonding strength of the solvent, and the solvent-to-feed ratio on organic acid separation efficiency. For an acetic acid-formic acid (AA-FA) mixture, the addition of high-boiling organic acids increases the relative volatility of FA over AA significantly. The addition of a Lewis base reverses the relative volatility, which depends on the applied solvent-to-feed ratio and the Lewis base BF3 affinity. For several binary acid mixtures (such as AA-FA and monochloroacetic acid-dichloroacetic acid), where the acids have a relatively big difference in acidity (ΔpKa ≥ 1), the separation selectivity appears practically independent of the acid strength of the individual acids and increases with increasing BF3 affinity of the Lewis base. For acid mixtures with a lower ΔpKa, a lower separation selectivity is obtained, as observed for separation of the pivalic acid-butyric acid and valeric acid-2-methyl butyric acid mixtures. When one of the acids in the mixture contains a secondary ketone group (i.e., levulinic acid in a levulinic acid-octanoic acid mixture), the strongest acid based on pKa is not necessarily attracted most by the added Lewis base. This, at first sight, unexpected behavior is most likely the result of complex intra- and intermolecular interactions and is quantitatively in line with COSMO-RS-based selectivity predictions.

Since the pioneering independent reports of Akiyama and Terada, the use of chiral phosphoric acids (CPAs) and derivatives as a versatile tool for asymmetric synthesis with good reactivity, regioselectivity, diastereoselectivity and enantioselectivity has emerged, forming an important part of the implementation of asymmetric counteranion-directed catalysis reported to date. In these achievements, the combination of metals with CPAs has enabled various catalytic modes beyond the scope of typical acid catalysis, such as relay catalysis, ion-pairing catalysis, and binary acid catalysis. The first-row transition metals (Sc–Zn) are considered to be sustainable transition metals and have received a great deal of attention. These naturally abundant metals display excellent Lewis acidity and function as powerful redox catalysts in synthesis involving both one and two-electron transfers. Hence, in this chapter, we summarize recent advances in the development of asymmetric reactions using a combination of first-row transition metals and CPAs. Furthermore, we provide a detailed discussion of the mechanisms involved in order to understand the interaction of the metal/phosphate and the origins of the asymmetric control of the transformations.

The exchange of the metal ion from In(III) to Sc(III) in a binary acid catalyst leads to a switch in the diastereoselectivity of [4 + 2] cycloadditions.

A mechanistic study of the tert-aminocyclization reaction was performed by using DFT calculations and labeling experiments. The results showed that the reaction proceeded through a rate-limiting-, stereospecific-, and suprafacial 1,5-H-transfer pathway, followed by a barrier-less C-C bond formation. The mode of stereocontrol for facial selection could be ruled out owing to the high activation energy of C-N bond rotation. The intrinsic feature of this Lewis acid activation was found to be the activation of the LUMO, as well as an intermediate-stabilization effect. The catalytically active species was believed to be a 1:1 complex of phosphoric acid and MgCl(2), which was stabilized by a H⋅⋅⋅Cl hydrogen bond. The chiral catalytic complex selectively recognizes and activates one of the two helical conformations of substrate A, required for 1,5-suprafacial H-transfer, which dictates the stereoselectivity of the forming products.

Swapping the anions of an indium Lewis acid leads to a remarkable regioselectivity switch between asymmetric 1,2- and 1,4-addition reactions of N-protected indoles (II) and β,γ-unsaturated α-keto esters (III).

A new binary acid system featuring an air stable organometallic precursor, titanocene dichloride and a simple Bronsted acid–base compound, was developed. The new catalyst system allowed for mild an...

This work deals with the study of corrosion behaviour for zinc in (HNO3+ H2SO4) binary acid mixture containing ethanolamines. Corrosion rate increases with concentration of acid and temperature. At constant acid concentration, the inhibition efficiency of ethanolamines increases with the inhibitor concentration. Value of ΔGa increases and inhibition decreases with temperature. The mode of inhibition action appears to be chemisorption.

A series of novel cross-linkers, N-hydroxysuccinimide (NHS)-activated end-bit binary acid (NHS-C4, C5, C6, C8, C10, C14), were synthesised to modify gelatin films and the crosslinking effects were compared. Homogeneous films with the exception of the film crosslinked by NHS-C14 were observed and the thickness was measured using a scanning electron microscope. The section feature influenced by different film-treatment conditions was also recorded. The differential scanning calorimetry results indicated higher thermal stability. The water contact angles confirmed enhanced hydrophobicity. NHS-C6, which was used as a probe crosslinker, exhibited the best crosslinking effect that the content of the free -NH2 achieved was the lowest out of all the crosslinkers. The biodegradation results of gelatin films modified by NHS-C6 exhibited better degradation-resistance and excellent stability. In addition, the optimal experimental conditions were 45°C for 12 h when [NHS-C6]/[-NH2] = 2.5.

A binary acid system has been developed that features an air-stable organometallic precursor, titanocene dichloride, and simple organic cooperative Bronsted acids, which allowed for mild and highly efficient Mannich reactions of both aryl and alkyl ketones with excellent yields and satisfactory diastereoselectivity. Mechanistic studies, including (1) H NMR titration, X-ray structure analyses as well as isolation of catalytically active species, elucidated the dramatic synergistic effects of this new binary acid system.

Equilibrium isotherms have been determined for the adsorption of two single-component and one binary acid dye solutions on carbon. The ideal adsorbed solute theory (IAST) has been used to predict isotherm data for the binary system using the single-component dye sorption data alone. A detailed analysis has been carried out to investigate the effect of different error criteria for determining single-component isotherm parameters and their influence on the results of IAS model simulations using the Langmuir and Freundlich isotherm equations. It was found that the “best-fit” single-component isotherm based on the minimum error criteria did not result in the “best-fit” IAS model predictions. Furthermore, the IAS model producing the closest fit to the binary experimental data did not use the same isotherm model as the single-component data for one dye. Reasons for this apparently anomalous behaviour have been discussed and the most likely cause appears to be dye–dye interactions in the binary system.

Recently, chiral Bronsted acids as dual ligand and acid catalysts in the context of metal catalysis have been developed. Such binary catalytic systems synergistically integrate chiral Bronsted acids and metal catalysts as a result of their weakly coordinating behaviors. The resulting binary acid catalysts have enabled effective reactions of a range of olefins/aromatics, beyond the scope of typical acid catalysis. Our endeavors in developing asymmetric binary acid catalysis are summarized in this feature article.

Selective H transfer by ABC: A new asymmetric binary acid catalyst was developed to promote 1,5-H transfer specifically and stereoselectively in tert-aminocyclization reactions with excellent activity, high enantioselectivity, and broad substrate scope. The H atom (in red) was proven to transfer through a stereospecific suprafacial pathway (see scheme).

Remote F effect: Unprecedented hetero-Diels-Alder reactions of mono- and bis-substituted cyclopentadienes have been realized by an asymmetric binary-acid catalyst that synergistically combines a chiral phosphoric acid 1 h/InBr(3) with good periselectivity, high regioselectivity, and excellent stereoselectivity. Substituent mapping of the chiral phosphoric acid indicates a dramatic remote ortho-fluoro effect on the stereocontrol.

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.

The title compound, C9H8O3, adopts a conformation in which both substituents lie nearly coplanar with the ring. Asymmetric units aggregate by centrosymmetric carboxyl pairing. Close offset stacking of rings in parallel planes creates inter­molecular C⋯C π–π contacts of 3.322 (3) and 3.352 (3) A, with an accompanying C⋯O π–π contact of 3.147 (3) A and similarly close inter­actions between O atoms and aromatic π systems. One close inter­molecular C—H⋯O contact is also present.

The properties of a water-soluble TTF dicarboxyl salt, Na2[C10H6O4S6]·3H2O, have been explored. The cyclic voltammogram of the salt shows two quasi-reversible redox waves at E1/2(1) = 0.280 V and E1/2(2) = 0.556 V with ΔE (Eox − Ere) = 78 and 68 mV, respectively, in H2O–CH3CN (1∶1 v/v). The redox potential of this compound is strongly dependent on the proton concentration. An ECEC square reaction, a redox-coupled association/dissociation of proton, was found for the second redox cycle. The redox active salt forms a mono-protonated anion in the pH range of 2–5. The calculated pKb constant of the salt is 5.93, corresponding to pKa(2) = 8.07 of the original binary acid. A single crystal structure of Bu4N[C10H7O4S6] was also obtained, which confirms that the mono-protonated compound has a stable conjugated structure.

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