RESUMEN

In this work, Glucomannan was modified with dopamine to synthesize a new polysaccharide Schiff base (GAD). After confirmation of GAD by NMR and FT-IR spectroscopic methods, it was introduced as a sustainable corrosion inhibitor with excellent anti-corrosion action for mild steel in 0.5 M hydrochloric acid (HCl) solution. Employing electrochemical test, morphology measurement, and theoretical analysis, the anticorrosion performance of GAD on mild steel in 0.5 M HCl solution is determined. Maximum efficiency of GAD for suppressing the corrosion rate of mild steel at 0.12 g L-1 reaches 99.0 %. After immersion in HCl solution for 24 h, the results from scanning electron microscopy indicate that GAD is firmly attached to the mild steel surface by making a protective layer. According to the X-ray photoelectron spectroscopy (XPS), FeN bonds existed on the steel surface indicate the presence of chemisorption between GAD and Fe to form stable complexes attracted to the active position on the mild steel. The effects of Schiff base groups on the corrosion inhibition efficiencies were also investigated. Moreover, the inhibition mechanism of GAD was further illustrated by the free Gibbs energy, quantum chemical calculation and molecular dynamics simulation.

Asunto(s)

Dopamina , Ácido Clorhídrico , Ácido Clorhídrico/química , Espectroscopía Infrarroja por Transformada de Fourier , Acero/química , Bases de Schiff , Ácidos

RESUMEN

Despite the widespread applications of α-hydroxyalkyl cyclic amines, direct and diverse access to such a class of unique vicinal amino alcohols still remains, to date, a challenge. Here, through a strategy of electroreductive α-hydroxyalkylation of inactive N-heteroarenes with ketones or electron-rich arylaldehydes, we describe a room temperature approach for the direct construction of α-hydroxyalkyl cyclic amines, which features a broad substrate scope, operational simplicity, high chemoselectivity, and no need for pressurized H2 gas and transition metal catalysts. The zinc ion generated from anode oxidation plays a crucial role in the activation of both reactants by decreasing their reduction potentials. The strategy of electroreduction in combination with substrate activation by Lewis acids in this work is anticipated to develop more useful transformations.

RESUMEN

Due to the generation of multiple intermediates during the nitroarene reduction, precise interception of single one to develop tandem reactions involving both C-C and C-N bond formations still remains a significant challenge. Herein, the relay catalysis of a supported bifunctional cobalt catalyst with l-proline has been successfully applied to establish a bran-new reductive annulation reaction of nitroarenes and formaldehyde, which enables direct and diverse construction of both symmetrical and unsymmetrical 1,3-diaryl imidazolines. It proceeds with operational simplicity, good substrate and functionality compatibility, and excellent step and atom-efficiency. Mechanistic studies reveal that the Co-catalyst exhibits a synergistic effect on the formation of key N-hydroxy imine, and the l-proline subsequently facilitates the key C-C bond formation. The current work opens a door to develop useful transformations with nitroarenes by reduction-interrupted strategy.

RESUMEN

Derivatization of azaarenes can create molecules of biological importance, but reductive functionalization of weakly reactive azaarenes remains a challenge. Here the authors show a dearomative, diastereoselective annulation of azaarenes, via ruthenium(II) reductive catalysis, proceeding with excellent selectivity, mild conditions, and broad substrate and functional group compatibility. Mechanistic studies reveal that the products are formed via hydride transfer-initiated ß-aminomethylation and α-arylation of the pyridyl core in the azaarenes, and that paraformaldehyde serves as both the C1-building block and reductant precursor, and the use of Mg(OMe)2 base plays a critical role in determining the reaction chemo-selectivity by lowering the hydrogen transfer rate. The present work opens a door to further develop valuable reductive functionalization of unsaturated systems by taking profit of formaldehyde-endowed two functions.

Asunto(s)

Rutenio , Catálisis , Hidrógeno , Estereoisomerismo

RESUMEN

Organic electrodes for low-cost potassium ion batteries (PIBs) are attracting more interest by virtue of their molecular diversity, environmental friendliness, and operation safety. But the sluggish potassium diffusion kinetics, dissolution in organic electrolyte, poor electronic conductivity, and low reversible capacities are several drawbacks compared with inorganic counterparts. Herein, the boronic ester based covalent organic framework (COF) material is successfully prepared on the exterior surface of carbon nanotubes (CNTs) via rational design of the organic condensation reaction and used as an anode material for PIBs. The few-layered structure of COF-10@CNT can provide more exposed active sites and fast K+ kinetics. It exhibits ultrahigh potassium storage performances (large reversible capacities of 288 mAh g-1 after 500 cycles at 0.1 A g-1 and 161 mAh g-1 after 4000 cycles at 1 A g-1), which is superior to previous organic electrodes and most inorganic electrodes. Moreover, the K-storage mechanism is proposed to be π-cation interaction between K+ and conjugated π-electrons of benzene rings.

RESUMEN

Aqua-coordinated sandwich-type polyoxometalates (POMs), {[WZnTM2(H2O)2](ZnW9O34)2} n- (TM=RhIII, PdII, and PtII), catalyze olefin epoxidation with hydrogen peroxide and have been well established, and they present an advance toward the utilization of olefins. To elucidate the epoxidation mechanism, we systematically performed density functional calculations. The reaction proceeds through a two-step mechanism: activation of H2O2 and oxygen transfer. The aqua-coordinated complexes show two distinct H2O2 activation pathways: "two-step" and "concerted". The concerted processes are more facile and proceed with similar and rate-determining energy barriers at the Rh-, Pd-, and Pt-containing transition states, which agrees well with the experimental results. Next, the resulting TM-OH-(µ-OOH) intermediate transfers an O atom to olefin to form an epoxide. The higher reactivity of the Rh-containing POM is attributed to more interactions between the Rh and hydroperoxo unit. We also calculated all active oxygen positions to locate the most favorable pathway. The higher reactivity of the two-metal-bonded oxygen position is predominantly ascribed to its lower stereoscopic hindrance. Furthermore, the presence of one and two explicit water solvent molecules significantly reduces the energy barriers, making these sandwich POMs very efficient for the olefin epoxidation with H2O2.