Latest ArticlesCarbocations such as tropylium and trityl cation, can be stable enough to be isolated and used without inert conditions. They can act as Lewis acids to lower the LUMO of electrophile, thus promoting reactions with nucleophiles. Additionally, the interaction between carbocations and alcohols can form Brønsted acids with enhanced acidity. Furthermore, electrophoto activation of TAC+ (trisaminocyclopropenium ion) delivers the excited radical dication TAC•2+*, which is a strong oxidant and capable of oxidizing a range of challenging substrates. Moreover, Pr-DMQA+ is disclosed as a versatile photoredox catalyst as its excited state can be quenched through both oxidation and reduction. This review summarizes recent advance in carbocation-catalyzed reactions. These developed methods provide an environmentally friendly pathway for the synthesis of valuable compounds and will inspire chemists to discover more interesting transformations promoted by carbocations.
A practical synthetic method for 4-thiocyanato-1H-pyrazoles through the electrochemical cascade reaction of hydrazines, 1, 3-diones and NH4SCN under metal-, chemical oxidant- and external electrolyte-free conditions was established. Importantly, both a gram-scale synthesis of 4-thiocyanato-1H-pyrazoles and five one-pot sequential transformations starting from hydrazine were successfully accomplished.
Thermally regenerative batteries (TRBs) are promising for harvesting low-grade waste heat into electrical power. However, the ammonia crossover from anode to cathode causes self-discharge and then leads to the decay of capacity. To alleviate the ammonia crossover and improve electricity generation, a stable graphene oxide (GO) modified anion exchange membrane (AEM) was proposed. Compared with the original AEM, the GO modified AEM with a 39.5% lower ammonia permeability induces a 24.3% higher maximal power output and 20.2% higher energy density in TRBs. Together with the visualization result, it was demonstrated the ammonia crossover was effectively alleviated by GO modifying the AEM not at a cost of the reduced battery performance, indicating the promising application in future TRBs.
With the help of the redox mediator, decoupled water-splitting allows O2 and H2 to be produced at different times, at different rates, and even in different cells, which promotes both the operation safety and the utilization of renewable power sources. However, the current densities and stabilities of these redox mediators are commonly low, which require further improvements for practical applications. Here, we propose to use supercapacitors as solid state redox mediators for decoupled water splitting. For demonstration, Na0.5MnO2 (pseudocapacitor) and active carbon (double layer capacitor), are both used as the redox mediator. These supercapacitors show superior current density (1 A/cm2) and ultralong cycle-life (8000 cycles) compared with commonly investigated battery-based mediators (NiOOH/Ni(OH)2). Our research proves supercapacitors can be used as redox relay with high current density and stability, which may bring new insights in the design of decoupled water splitting systems.
Waste generation from food manufacturing facilities poses a serious hazard like environmental degradation, water pollution, and land pollution due to its high nutrient composition. Specifically, solid waste (powder) disposal requires additional energy sources in terms of scientific treatment, structured collection, and disposal packaging according to the safety regulation. Thus, this research discusses the viewpoint of integrating food processing waste as an organic carbon source with BG-11 medium for Chlorella vulgaris (FSP-E) growth. The food processing waste powders investigated in this study were obtained from milk, and biscuit manufacturing facilities. The culture medium was modified by combining both BG-11 and food processing waste powders to identify the optimal algal growth and biochemical content. Compared to the microalgae grown in BG-11 alone (IBG), the combination of biscuit waste and IBG produced higher biomass concentration (44%), with increased lipid (11%), protein (20%), and carbohydrate (57%) contents. Chlorella vulgaris was able to uptake nutrients from the culture medium with combination of food processing waste and IBG thus enhancing its growth. The results obtained also indicate that an integrated culture system using food processing waste and synthetic sources can generate energy out of waste by improving the bio-composition of the microalgae biomass.
Polyanilines (PANIs) can be easily prepared from the available and cheap anilines via the oxidative polymerization reactions. Owing to the coordination of nitrogen in the material with metals, PANIs are widely used as the support of nano metal catalysts. In comparison with inorganic supports, the nano metals on PANIs were firmly anchored via the coordination bond so that they are not easily to lose during the reaction process. Moreover, since PANIs are versatile materials and their chemical features can be adjusted by introducing functional groups onto the monomers, the catalytic activities of the prepared catalysts are tunable. During the past decade, PANIs-supported nano metal catalysts have been widely applied in a variety of coupling reactions. This review aims to summarize the recent advances and give a perspective.
Hierarchical carbon material is used as a star cocatalyst in the field of photocatalysis due to its excellent catalytic properties. In this work, mesoporous carbon nitride sheet (MCNS) photocatalyst introduced nitrogen-doped hollow carbon spheres assembled with cobalt nanoparticles (Co@NHC) is synthesized by electrostatic adsorption. A series of characterizations are analyzed to display the structures, morphologies and optical properties of as-prepared materials. The photocatalytic activity of Co@NHC/MCNS material is evaluated with hydrogen evolution under visible light irradiation. The results indicate that 5 wt% Co@NHC/MCNS material reveals higher photocatalytic activity of hydrogen evolution rate of 3675 µmol/g with 4 h reaction time, which is 159 times than that of pure MCNS material. The carbon material with excellent charge transport properties can effectively accelerate the charge transfer from ultrathin MCNS to cobalt nanoparticles. The goal of improving the photocatalytic performance of Co@NHC/MCNS material is achieved. As a result, it provides a feasible and promised approach for doping transition metals to enhance photocatalytic activity.
Dinitrogen activation under mild conditions is important but extremely challenging due to the inert nature of the N≡N triple bond evidenced by high bond dissociation energy (945 kJ/mol) and large HOMO-LUMO gap (10.8 eV). In comparison with largely developed transition metal systems, the reported main group species on dinitrogen activation are rare. Here, we carry out density functional theory calculations on methyleneboranes to understand the reaction mechanisms of their dinitrogen activation. It is found that the methyleneboranes without any substituent at the boron atom performs best on dinitrogen activation, which could be contributed to its small singlet-triplet gap. In addition, strong correlations are achieved on dinitrogen activation between the singlet-triplet energy gap and the reaction energies for the formation of the end-on products as well as the side-on ones. The principal interacting orbital analysis suggests that methyleneboranes can mimic transition metals to cleave the NN triple bond. Our findings could be helpful for experimental chemists aiming at dinitrogen activation by main group species.
Atom- and step-economy in IBX assisted diversity-oriented synthesis is achieved with a versatile AQ auxiliary α-amino acid analogs offering rapid access to polycyclic spiro-quinolines featuring a quaternary stereocenter in 20%–91% yields under mild conditions via 7, 8-dearomatization of quinolines. Free of a preinstalled activation group is highlight of this intramolecular oxidation spiroannulation tandem reaction. This type of N-heterospirocycles, traditionally difficult to access, may open the door to a potentially interest scaffold for synthetic and medicinal chemistry.
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