Electrochemical hydrogenation and oxidation of organic species involving water.

Fossil fuel-driven thermochemical hydrogenation and oxidation using high-pressure H2 and O2 are still popular but energy-intensive CO2-emitting processes. At present, developing renewable energy-powered electrochemical technologies, especially those using clean, safe and easy-to-handle reducing agents and oxidants for organic hydrogenation and oxidation reactions, is urgently needed. Water is an ideal carrier of hydrogen and oxygen. Electrochemistry provides a powerful route to drive water splitting under ambient conditions. Thus, electrochemical hydrogenation and oxidation transformations involving water as the hydrogen source and oxidant, respectively, have been developed to be mild and efficient tools to synthesize organic hydrogenated and oxidized products. In this Review, we highlight the advances in water-participating electrochemical hydrogenation and oxidation reactions of representative organic molecules. Typical electrode materials, performance metrics and key characterization techniques are firstly introduced. General electrocatalyst design principles and controlling the microenvironment for promoting hydrogenation and oxygenation reactions involving water are summarized. Furthermore, paired hydrogenation and oxidation reactions are briefly introduced before finally discussing the challenges and future opportunities of this research field.

Alkynes Electrooxidation to α,α-Dichloroketones in Seawater with Natural Chlorine Participation via Competitive Reaction Inhibition and Tip-Enhanced Reagent Concentration.

The traditional synthesis of α,α-dichloroketones usually requires corrosive chlorine, harsh reaction conditions, or excessive electrolytes. Here, we report an electrooxidation strategy of ethynylbenzenes to α,α-dichloroketones by directly utilizing seawater as the chlorine source and electrolyte solution without an additional supporting electrolyte. High-curvature NiCo2O4 nanocones are designed to inhibit competitive O2 and Cl2 evolution reactions and concentrate Cl- and OH- ions, accelerating α,α-dichloroketone electrosynthesis. NiCo2O4 nanocones produce 81% yield, 61% Faradaic efficiency, and 44.2 mmol gcat.-1 h-1 yield rate of α,α-dichloroketones, outperforming NiCo2O4 nanosheets. A Cl• radical triggered Cl• and OH• radical addition mechanism is revealed by a variety of radical-trapping and control experiments. The feasibility of a solar-powered electrosynthesis system, methodological universality, and extended synthesis of α,α-dichloroketone-drug blocks confirm its practical potential. This work may provide a sustainable solution to the electrocatalytic synthesis of α,α-dichloroketones via the utilization of seawater resources.

Membrane-Free Electrosynthesis of Epichlorohydrins Mediated by Bromine Radicals over Nanotips.

The industrial manufacture of epichlorohydrin (ECH) often suffers from excessive corrosive chlorine and multistep processes. Here, we report a one-pot membrane-free Br radical-mediated ECH electrosynthesis. Bromine radicals electro-oxidized from Br- ions initiate the reaction and then eliminate HBr from bromohydrin to give ECH and release Br- ions for reuse. A high energy barrier for *OH oxidation and isolated Br adsorption sites enables NiCo2O4 to suppress the competitive oxygen and bromine evolution reactions. The high-curvature nanotips with an increased electric field concentrate Br- and OH- ions to accelerate ECH electrosynthesis. This strategy delivers ECH with a Faradaic efficiency of 47% and a reaction rate of 1.4 mol h-1 gcat-1 at a high current density of 100 mA cm-2, exceeding the profitable target from the techno-economic analysis. Economically profitable electrosynthesis, methodological universality, and the extended synthesis of epoxide-drug blocks highlight their promising potential.

Formamide Electrosynthesis from Methanol and Ammonia in Water over Pr-Doped MnO2.

A rare earth element doping strategy is reported to boost the activity and enhance the stability of MnO2 for selective formamide production through electrocatalytic oxidation coupling (EOC) of methanol and ammonia. MnO2 doped with 1% Pr was selected as the best candidate with an optimized formamide yield of 211.32 µmol cm-2 h-1, a Faradaic efficiency of 22.63%, and a stability of more than 50 h. The easier formation of Mn6+ species and the lower dissolution rate of Mn species over Pr-doped MnO2 revealed by in situ Raman spectra were responsible for the boosted formamide production and enhanced stability. In addition, a two-electrode flow electrolyzer was developed to integrate EOC with C2H2 semihydrogenation for simultaneously producing value-added products in both the anode and cathode.

Designed Nanomaterials for Electrocatalytic Organic Hydrogenation Using Water as the Hydrogen Source.

ConspectusThe hydrogenation reaction is one of the most frequently used transformations in organic synthesis. Electrocatalytic hydrogenation by using water (H2O) as the hydrogen source offers an efficient and sustainable approach to synthesize hydrogenated products under ambient conditions. Such a technique can avoid the use of high-pressure and flammable hydrogen gas or other toxic/expensive hydrogen donors, which usually cause environmental, safety, and cost concerns. Interestingly, utilizing easily available heavy water (D2O) for deuterated syntheses is also attractive due to the widespread applications of deuterated molecules in organic synthesis and the pharmaceutical industry. Despite impressive achievements, electrode selection mainly relies on trial-and-error modes, and how electrodes dictate reaction outcomes remains elusive. Therefore, the rational design of nanostructured electrodes for driving the electrocatalytic hydrogenation of a series of organics via H2O electrolysis is developed.In this Account, we review recent advances in the electrocatalytic hydrogenation of different types of organic functional groups, including C≡C, C≡N, C═C, C═O, and C-Br/I bonds, -NO2, and N-heterocycles, with H2O over nanostructured cathodes. First, the general reaction steps (reactant/intermediate adsorption, active atomic hydrogen (H*) formation, surface hydrogenation reaction, product desorption) are analyzed, and key factors are proposed to optimize hydrogenation performance (e.g., selectivity, activity, Faradaic efficiency (FE), reaction rate, and productivity) and inhibit side reactions. Then, ex situ and in situ spectroscopic tools to study key intermediates and interpret mechanisms are introduced. Third, based on the knowledge of key reaction steps and mechanisms, we introduce catalyst design principles in detail on how to optimize the adoption of reactants and key intermediates, promote the formation of H* from water electrolysis, inhibit hydrogen evolution and side reactions, and improve the selectivity, reaction rate, FEs, and space-time productivity of products. We then introduce some typical examples. (i) P- and S-modified Pd can decrease C═C adsorption and promote H* formation, enabling semihydrogenation of alkynes with high selectivity and FEs at lower potentials. Then, creating high-curvature nanotips to concentrate the substrates further speeds up the hydrogenation process. (ii) By introducing low-coordination sites into Fe and combining low-coordination sites and surface fluorine to modify Co to optimize the adsorption of intermediates and facilitate H* formation, hydrogenation of nitriles and N-heterocycles with high activity and selectivity is obtained. (iii) By forming isolated Pd sites to induce a specific σ-alkynyl adsorption of alkynes and steering S vacancies of Co3S4-x to preferentially adsorb -NO2, hydrogenation of easily reduced group-decorated alkynes and nitroarenes with high chemoselectivity is realized. (iv) For gas reactant participated reactions, by designing hydrophobic gas diffusion layer-supported ultrasmall Cu nanoparticles to enhance mass transfer, improve H2O activation, inhibit H2 formation, and decrease ethylene adsorption, ampere-level ethylene production with a 97.7% FE is accomplished. Finally, we provide an outlook on the current challenges and promising opportunities in this area. We believe that the electrode selection principles summarized here provide a paradigm for designing highly active and selective nanomaterials to achieve electrocatalytic hydrogenation and other organic transformations with fascinating performances.

Electrosynthesis of a nylon-6 precursor from cyclohexanone and nitrite under ambient conditions.

Cyclohexanone oxime, an important nylon-6 precursor, is conventionally synthesized through cyclohexanone-hydroxylamine (NH2OH) and cyclohexanone ammoxidation methodologies. These strategies require complicated procedures, high temperatures, noble metal catalysts, and toxic SO2 or H2O2 usage. Here, we report a one-step electrochemical strategy to synthesize cyclohexanone oxime from nitrite (NO2-) and cyclohexanone under ambient conditions using a low-cost Cu-S catalyst, avoiding complex procedures, noble metal catalysts and H2SO4/H2O2 usage. This strategy produces 92% yield and 99% selectivity of cyclohexanone oxime, comparable to the industrial route. The reaction undergoes a NO2- → NH2OH→oxime reaction pathway. This electrocatalytic strategy is suitable for the production of other oximes, highlighting the methodology universality. The amplified electrolysis experiment and techno-economic analysis confirm its practical potential. This study opens a mild, economical, and sustainable way for the alternative production of cyclohexanone oxime.

A Facile Strategy for Constructing a Carbon-Particle-Modified Metal-Organic Framework for Enhancing the Efficiency of CO2 Electroreduction into Formate.

Electrocatalytic reduction of CO2 by metal-organic frameworks (MOFs) has been widely investigated, but insufficient conductivity limits application. Herein, a porous 3D In-MOF {(Me2 NH2 )[In(BCP)]⋅2 DMF}n (V11) with good stability was constructed with two types of channels (1.6 and 1.2 nm diameter). V11 exhibits moderate catalytic activity in CO2 electroreduction with 76.0 % of Faradaic efficiency for formate (FEHCOO- ). Methylene blue molecules of suitable size and pyrolysis temperature were introduced and transformed into carbon particles (CPs) after calcination. The performance of the obtained CPs@V11 is significantly improved both in FEHCOO- (from 76.0 % to 90.1 %) and current density (2.2 times). Control experiments show that introduced CPs serve as accelerant to promote the charges and mass transfer in framework, and benefit to sufficiently expose active sites. This strategy can also work on other In-MOFs, demonstrating the universality of this method for electroreduction of CO2 .

Unveiling the Activity Origin of Iron Nitride as Catalytic Material for Efficient Hydrogenation of CO2 to C2+ Hydrocarbons.

Developing efficient catalytic materials and unveiling the active species are significant for selective hydrogenation of CO2 to C2+ hydrocarbons. Fe2 N@C nanoparticles were reported to exhibit outstanding performance toward selective CO2 hydrogenation to C2+ hydrocarbons (C2+ selectivity: 53.96 %; C2 -C4 = selectivity, 31.03 %), outperforming corresponding Fe@C. In situ X-ray diffraction, ex situ Mössbauer and X-ray photoelectron spectra revealed that iron nitrides were in situ converted to highly active iron carbides, which acted as the real active species. Moreover, the combined results of in situ diffuse reflectance infrared Fourier transform spectroscopy and control experiments suggested an in situ formed carbonyl iron-mediated conversion mechanism from iron nitrides to iron carbides.

The interaction of imidazole-, imidazolium-, and tetrazolium-containing compounds with DNA.

The interaction between DNA and members of series of bivalent imidazole compounds, monovalent and bivalent imidazolium compounds, and monovalent and bivalent tetrazolium compounds, which had been synthesized and evaluated for their anti-Plasmodium activity, has been examined using the displacement of SYBR Green I as a measure of competitive binding. The degree of interaction with DNA appears to be dependent on both hydrophobic and charge-pairing interactions.