Spontaneous Dehydrogenation Research Articles

Accelerating alcohol oxidation kinetics for electrochemical biomass upgrading via photoinduced active CuIII-O generation

Copper-based compounds exhibit broad prospects in the electrocatalytic oxidation of biomass for sustainable production of high-value-added chemicals due to their passivated oxygen evolution reaction (OER) competitiveness. However, the sluggish reaction kinetics remain the main challenge in constraining their scalable application. Herein, a highly selective electrooxidation of 5-hydroxymethylfurfural (HMF) to 2, 5-furandicarboxylic acid (FDCA) on CuO is achieved via photoinduced surface reconstruction. The experimental results confirmed that the photogenerated hole accumulation on the surface of CuO with matched valence band position can promote the CuOOH active phase generation. Density functional theory (DFT) calculations and the overall relationship between structure and selectivity indicate the CuOOH species can accelerate the spontaneous dehydrogenation process of hydroxyl group. Therefore, the activated CuO electrode under illumination can effectively regulate the conversion of 5-Hydroxymethyl-2-furancarboxylic acid (HMFCA) key intermediates and exhibits accelerated reaction kinetics, FDCA yield increased by 17.79 % compared to dark condition. Additionally, a general enhancement effect on the oxidation of benzyl alcohol and furfuryl alcohol was also revealed. This work introduces photoassistance effect for the first time in HMF oxidation, opening up prospects for the application of photoelectric synergy in biomass value-added conversion and providing insights into the activity mechanism of Cu-based catalysts in organic oxidation.

Revealing the Electro-oxidation Mechanism of 5-Aminotetrazole on Nickel-Based Oxides and Synthesizing 5,5'-Azotetrazolate Salts.

With the gradual expansion of the application of organic electromechanical synthesis in the field of energetic materials, it is necessary to explore deeply the mechanisms behind the organic electromechanical oxidation of energetic materials in order to develop efficient electrocatalysts. Electrochemical synthesis of 5,5'-azotetrazolate (ZT) salts is not only environmentally friendly and efficient but also can replace oxygen evolution reaction (OER) combined with hydrogen production, significantly reducing the battery voltage of overall water splitting (OWS) and achieving low energy consumption hydrogen production. Here, we prepared the Co-modified nickel-based oxide electrodes (Ni3-xCoO4/carbon cloth (CC), x = 1, 2) as a medium to reveal the oxidative coupling mechanism of 5-aminotetrazole (5-AT). Experimental and theoretical calculations verified that Ni-catalyzed oxidative coupling of 5-AT is a proton-coupled electron transfer (PCET) process, including electron transfer of electrocatalytic intermediates (Ni2+-O + OH- = Ni3+-O(OH) + e-) and spontaneous dehydrogenation process (Ni3+-O(OH) + X-H = Ni2+-O + X•). The Ni3+-O(OH) is an extremely fast nonreducing electron transfer center that serves as a chemical oxidant to directly abstract hydrogen atoms from the 5-AT. Simultaneously, the synergistic effect of Co doping on the electric cloud around Ni causes the upshift of the d-band centers, which is conducive to the easier adsorption of OH*, forming the generation of active intermediate Ni3+-O(OH). Thus, Ni2CoO4/CC has higher Faraday efficiency (FE) and yield for the oxidation reaction of 5-AT, with a yield of approximately 72.3% after electrolysis at 1.7 V vs reversible hydrogen electrode (RHE).

Probing hydrogen content in steel using the thermoelectric effect

The issue of hydrogenation of steel is a serious technological problem. Due to its small atomic radius, hydrogen is difficult to analyze quantitatively and qualitatively. Non-destructive estimation of hydrogen content would significantly improve the quality control process. In this work, we attempt to develop a new methodology for the determination of hydrogen content in 4340 steel using the thermoelectric effect. For this purpose, we investigated the mechanisms of hydrogenation, structural and microstructural changes caused by hydrogenation, and performed theoretical calculations of the influence of hydrogen on the electronic structure of steel. Measurements of the Seebeck coefficient were performed using the specially developed μm-resolution scanning thermoelectric microscope (SThM). The KKR-CPA calculations show that hydrogen located at T-voids strongly modifies electronic properties and influences the Seebeck coefficient of the material. Ultraviolet photoelectron spectroscopy (UPS) proves that hydrogenated samples exhibit the valence band onset shift towards higher binding energies concerning the non-hydrogenated materials. Theoretical and experimental studies of the Seebeck coefficient dependence on the total hydrogen content confirm a measurable decrease in the Seebeck coefficient (18.5 µV/K for 0.136 ppm and 13.5 µV/K for 1.03 ppm). Plotted calibration curves for 4340 steel were used for preliminary kinetic studies of the spontaneous dehydrogenation in this material. This work demonstrates that the thermoelectric effect can be used as the basis of a new fast and non-destructive analytical method for the determination of the hydrogen content in 4340 steel.

A mathematical model for dehydrogenation of molten steel in the Vacuum degasser

This paper presents a mathematical model of VD dehydrogenation aimed at predicting hydrogen removal during the VD vacuum refining process and investigating the effect of controllable parameters on the dehydrogenation process. Taking into account the behavior of argon bubbles during their uplifting, the model considers that the dehydrogenation reaction occurs at three sites, the surface of the Ar bubbles, the bath surface of the molten steel, and the bulk steel. The calculated results are in good agreement with the industrial production data. The hydrogen content of the molten steel during VD dehydrogenation is observed to vary as an inversely proportional function with the vacuum holding time, decreasing rapidly in the early stage and slowing down in the later stage. Using the model, the contribution of different reaction sites to the dehydrogenation process was investigated. It was found that the internal spontaneous nucleation of the molten steel dominated the dehydrogenation process at the beginning. Then, the internal spontaneous nucleation gradually weakened to disappear as the hydrogen content of the molten steel decreased, followed by the dominance of dehydrogenation on the surface of the Ar bubble. The model also investigated the effect of vacuum pressure and argon flow rate on the VD dehydrogenation process. It was found that the vacuum pressure significantly influenced the dehydrogenation rate on the Ar bubble surface and the bath surface mainly by affecting the equilibrium hydrogen concentration in the gas phase and by influencing the critical nucleation depth, which affected the internal spontaneous dehydrogenation. Moreover, the increase of the argon flow rate not only increases the reaction area of the Ar bubble but also the reaction area at the activation zone on the bath surface. Additionally, the increase of the initial hydrogen content in the molten steel significantly promotes the spontaneous dehydrogenation of the internal nucleation in the bulk steel.

Flavoprotein StnP2 Catalyzes the β-Carboline Formation during the Streptonigrin Biosynthesis.

β-Carboline (βC) alkaloids constitute a large family of indole alkaloids that exhibit diverse pharmacological properties, such as antitumor, antiviral, antiparasitic, and antimicrobial activities. Here, we report that a flavoprotein StnP2 catalyzes the dehydrogenation at C1-N2 of a tetrahydro-β-carboline (THβC) generating a 3,4-dihydro-β-carboline (DHβC), and the DHβC subsequently undergoes a spontaneous dehydrogenation to βC formation involved in the biosynthesis of the antitumor agent streptonigrin. Biochemical characterization showed that StnP2 catalyzed the highly regio- and stereo-selective dehydrogenation, and StnP2 exhibits promiscuity toward different THβCs. This study provides an alternative kind of enzyme catalyzing the biosynthesis of βC alkaloids and enhances the importance of flavoproteins.

Continuous soot surface growth over carbene active site through spin density migration and spontaneous dehydrogenation: A DFT study

Surface growth process contributes the majority of soot mass, but the detailed mechanism remains vague, especially at post-flame zone where reactive radicals like H· are insufficient to continuously generate active sites. In this work, the reactivity of carbene active center on soot surface towards different categories of hydrocarbons was evaluated through DFT calculation, and the self-sustaining mechanisms for continuous further growth were proposed. Acetylene, aromatic molecules (benzene and naphthalene) and resonance stabilized radicals (RSRs, cyclopentadienyl and indenyl) were selected as representative reactants. Potential energy surfaces were obtained at the M06-2X/cc-pVTZ level of theory, and spin density distributions were presented to analyze the evolution of active sites. The surface growth process was divided into two stages, i.e., initial capture and further growth. During initial capture process, carbene active site exhibits high reactivity towards all kinds of representative reactants, and the energy barriers are lower than 10 kJ/mol except for benzene (26.17 kJ/mol). Meanwhile, the initial capture processes are exothermic and capturing RSRs shows the largest exothermicity. After the carbene site was occupied through initial capture process, the graphene flake still tends to retain the radical-like behavior and shows open-shell character, providing possibilities for further surface growth. During further growth process, spin density migration mechanism combined with spontaneous dehydrogenation step could achieve continuous surface capture without involving exogenous radicals. For acetylene, the unpaired electrons will preferentially locate at the terminal carbon of the growing chain to continuously refresh the active site. Extra dehydrogenation steps are required for the further growth involving aromatics and RSRs, otherwise the surface growth steps would be less exothermic and more reversible. Covalent bonding of these sp2-hybridized hydrocarbon species and the carbene site will create a vulnerable tertiary CH bond. Spontaneous dehydrogenation through the breakage of the tertiary CH bond can reproduce active site with localized spin density, after which the further growth process will be energetically and kinetically more feasible.

A Brønsted Acidic Gallium Hydride: Facile Interconversion of NNNN-Macrocycle Supported [GaI ]+ and [GaIII H]2.

Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me4TACD)H][BAr4 Me] (Me4TACD=N,N′,N′′,N′′′‐tetramethyl‐1,4,7,10‐tetraazacyclododecane; [BAr4 Me]−=[B{C6H3‐3,5‐(CH3)2}4]−) provided monovalent salts [(Me4TACD)M][BAr4 Me], whereas [Cp*Al]4 yielded trivalent [(Me4TACD)AlH][BAr4 Me]2. Protonation of [(Me4TACD)Ga][BAr4 Me] with [Et3NH][BAr4 Me] gave an unusually acidic (pK a(CH3CN)=24.5) gallium(III) hydride dication [(Me4TACD)GaH][BAr4 Me]2. Deprotonation with IMe4 (1,3,4,5‐tetramethyl‐imidazol‐ylidene) returned [(Me4TACD)Ga][BAr4 Me]. These reversible processes occur with formal two‐electron oxidation and reduction of gallium. DFT calculations suggest that gallium(I) protonation is facilitated by strong coordination of the tetradentate ligand, which raises the HOMO energy. High nuclear charge of [(Me4TACD)GaH]2+ facilitates hydride‐to‐metal charge transfer during deprotonation. Attempts to prepare a gallium(III) dihydride cation resulted in spontaneous dehydrogenation to [(Me4TACD)Ga]+.

Hydrogenation Dynamics of Electrically Controlled Metal–Insulator Transition in Proton‐Gated Transparent and Flexible WO3 Transistors

AbstractElectrolyte gating is widely adopted to electrically control the physical properties of materials, leading to numerous intriguing phenomena and various applications. However, the carrier modulation mechanism remains heavily controversial. Herein, using natural mica pieces as substrates and ionic gel as the dielectric layer, all‐transparent and flexible WO3 transistor configuration is designed to in situ monitor the dynamic doping process of electrolyte gating. A reversible and vacuum‐dominant volatile/nonvolatile metal–insulator transition (MIT) is observed in electrolyte‐gated WO3 thin films. In situ X‐ray diffraction experiments, together with first‐principles calculations, reveal an abrupt and symmetric structural evolution through two distinct hydrogenated metastable phases and phase separation progress. The fast volatility is assigned to a spontaneous dehydrogenation process. A prototype of a flexible vacuum meter is demonstrated on the basis of the unique vacuum‐dependent MIT, exhibiting a measurement range down to 1.0 × 10−6 mbar and no injury of electromagnetic radiation. These findings bring new insights into hydrogenation dynamics, paving a feasible way for the realization of user‐friendly flexible electronics.

First thia-Diels-Alder reactions of thiochalcones with 1,4-quinones.

Aryl and hetaryl thiochalcones react smoothly with 1,4-quinones in THF solution at 60 °C yielding the corresponding fused 4H-thiopyrans after spontaneous dehydrogenation of the initially formed [4 + 2] cycloadducts. In general, the yields of the isolated products were high. With 5-chloro-10-hydroxy-1,4-anthraquinone, the thia-Diels–Alder reaction occurred with complete regioselectivity. In the case of the reaction of vitamin K3 (menadione) with diphenylthiochalcone, the initial cycloadduct was isolated in 37% yield.

Acceptor Behavior and E–H Bond Activation Processes of the Unsaturated Heterometallic Anion [MoReCp(μ-PCy2)(CO)5]−(Mo═Re)

The ability of the title anion to act as an acceptor of simple donors and to participate in E–H bond activation processes (E = p-block element) was analyzed by examining its reactions with PPh2H, HSPh, and HCC(p-tol). The sodium salt of this anion (1-Na) reacted with PPh2H to give the electron-precise derivative Na[MoReCp(μ-PCy2)(CO)5(PPh2H)], with the added ligand trans to the PCy2 group. The latter reacted with (NH4)PF6 to give the hydride-bridged derivative mer-[MoReCp(μ-H)(μ-PCy2)(CO)5(PPh2H)], which was dehydrogenated photochemically to give first the known compound [MoReCp(μ-PCy2)(μ-PPh2)(CO)5] and then the new complex [MoReCp(μ-O)(μ-PCy2)(μ-PPh2)(CO)3], with a strongly asymmetric bridging oxide ligand (Mo–Re = 2.8640(6) A). The reaction of 1-Na with HSPh involved protonation and ligand addition to give the thiol complex [MoReCp(μ-H)(μ-PCy2)(CO)5(HSPh)], which underwent spontaneous dehydrogenation to give the thiolate derivative [MoReCp(μ-PCy2)(μ-SPh)(CO)5] (Mo–Re = 2.9702(8) A), having a quite puck...

Task‐specific Ionic Liquid Mediated Eco‐compatible Approach for the Synthesis of Spirooxindole Derivatives and Their DNA Cleavage Activity

Guanidine‐based task‐specific ionic liquid 1,1,3,3‐tetramethylguanidine acetate [TMG][Ac]was found to be a very effective solvent for the synthesis of pharmaceutically important spirooxindole derivatives through one‐pot multicomponent reaction of substituted isatin, thiazolidine‐4‐carboxylic acid and naphthoquinone followed by the spontaneous dehydrogenation in excellent yields without using any reagent and catalyst. The TMG‐based ionic liquid could be recovered and used at least four times without considerable reduction in its activity. The advantageous features of the developed synthetic protocol are high atom economy, operational simplicity, shorter reaction time, easily handling, and environmentally benign. The structure and relative stereochemistry of final products was established by single crystal X‐ray structure and spectroscopic techniques. The synthesized compounds were subjected for DNA cleavage activity.

Influence of spontaneous decomposition on the electrochemical formic acid oxidation on a nanostructured palladium electrode

The formic acid electrooxidation reaction was studied in a flow cell in 1M HCOOH–0.5M H2SO4 solution on a palladium film electrode. The evaluation of the open circuit potential (OCP) decay demonstrated that the spontaneous dehydrogenation of formic acid is quickly verified, leading to hydrogen adsorption and absorption. Moreover, the absence of carbon containing adsorbed species was verified by the application of voltammetric stripping after OCP and chronoamperometry. The results obtained demonstrate that the electrocatalytic oxidation of formic acid on Pd takes place through the spontaneous HCOOH dissociative adsorption with CO2 evolution and the adsorbed hydrogen electrooxidation.

ChemInform Abstract: A Simple Heterocyclic Fusion Reaction and Its Application for Expeditious Syntheses of Rutaecarpine and Its Analogues.

AbstractRutaecarpine (IIIa) and various analogs are prepared from anhydrides (I) and (VI) with cyclic imines via a simple heterocyclic fusion reaction which involves a spontaneous dehydrogenation.

A simple heterocyclic fusion reaction and its application for expeditious syntheses of rutaecarpine and its analogs

In the search for new inhibitors of cholinesterases, a simple heterocyclic fusion reaction of isatoic anhydride 8 and 3,4-dihydroisoquinoline 22 was discovered which involves a spontaneous dehydrogenation upon heating. Applying the reaction, the bioactive natural alkaloid rutaecarpine and several substituted derivatives out of tryptamines and anthranilic acids or isatoic anhydrides, respectively, can be synthesized without tedious chromatographic purification. This provides simple and fast access to larger amounts of compounds with this privileged structure in medicinal chemistry.

ChemInform Abstract: Spontaneous Dehydrogenation of 2‐Hydrazinoethyl‐ and 4‐Hydrazinobut‐2‐enylphosphonium Salts.

AbstractThe reaction of phosphonium salt (III) under various reaction conditions is studied.

Spontaneous dehydrogenation of 2-hydrazinoethyl- and 4-hydrazinobut-2-enylphosphonium salts

2-Hydrazinoethyl- and 4-hydrazinobut-2-enylphosphonium salts undergo spontaneous dehydrogenation leading to the corresponding hydrazones or diazenes, depending on the structure of the starting compounds or the reaction conditions. A possible mechanism of the trans-formations is discussed.

ChemInform Abstract: Synthesis of Novel Spirooxindole Derivatives by One Pot Multicomponent Reaction and Their Antimicrobial Activity.

Abstract1,3‐Dipolar cycloaddition of azomethine ylides, generated in situ via decarboxylative condensation of isatins (I) and (IX) and sarcosine (II) or (L)‐proline (X), to naphthoquinone (III), followed by spontaneous dehydrogenation afford the spirooxindoles (IV) and (XI), resp., in high yields.

Synthesis of novel spirooxindole derivatives by one pot multicomponent reaction and their antimicrobial activity

A series of novel spirooxindoles have been synthesized through 1,3-dipolar cycloaddition of an azomethine ylide generated from isatin and sarcosine or l-proline with the dipolarophile 1,4-naphthoquinone followed by spontaneous dehydrogenation. Synthesised compounds were evaluated for their antimicrobial activities against eight bacteria and three fungi. All the spirooxindole derivatives exhibited significant antibacterial activity against Staphylococcus aureus, S. aureus (MRSA), Enterobacter aerogens, Micrococcus luteus, Proteus vulgaris, Klebsiella pneumonia, Salmonella typhimurium, Salmonella paratyphi-B and anti-fungal activity against Malassesia pachydermatis, Candida albicans and Botyritis cinerea organisms. Among 23 compounds screened, 1′-acetyl-2,5′-dimethyl-2,3-dihydrospiro[benzo[f]isoindole-1,3′-indoline]-2′,4,9-trione was found to be more active against tested bacteria and fungi.

Synthesis and Decarbonylation Reactions of Diiron Cyclopentadienyl Complexes with Bent-Phosphinidene Bridges

The phosphinidene complexes [Fe2Cp2(μ-PR)(μ-CO)(CO)2] (Cp = η5-C5H5; R=Cy, Ph, Mes, Mes*; Mes = 2,4,6-C6H2Me3, Mes* = 2,4,6-C6H2tBu3) were readily prepared in high yields through a two-step procedure starting from the corresponding phosphine complexes [Fe2Cp2(μ-CO)2(CO)(PH2R)]. When R = Cy, Ph, Mes, the first step required the oxidation of the phosphine complex with 1 equiv of [FeCp2]BF4, this being followed by spontaneous dehydrogenation to yield the cationic phosphide complexes [Fe2Cp2(μ-PHR)(μ-CO)(CO)2]BF4, while the formation of the related PMes*H-bridged complex required a double oxidation of the corresponding neutral precursor in the presence of a deprotonating agent. In all cases the final step involved the deprotonation of the above cations with strong bases such as M(OH) (M = Na, K). Attempts to decarbonylate the above phosphinidene complexes by either thermolysis or photolysis in solution gave results strongly dependent on the nature of R. Thus, the photolysis of the cyclohexylphosphinidene complex gave a mixture of the clusters [Fe4Cp4(μ3-PCy)2(μ3-CO)(μ-CO)(CO)] (Fe−Fe distances 2.6115(7) and 2.5332(8) Å) and [Fe3Cp3(μ3-PCy)(μ-PCyH)(μ-CO)2], while the thermal decarbonylation of the mesitylphosphinidene complex in refluxing toluene gave the trinuclear derivative [Fe3Cp3(μ-PMes)(μ-PMesH)(μ-CO)2(CO)], having a trigonal phosphinidene ligand bridging two iron atoms (Fe−P = 2.161(8), 2.165(8) Å). The formation of all these compounds presumably involves the participation of the corresponding intermediate complex [Fe2Cp2(μ-PR)(μ-CO)2], a species likely to contain a trigonal (four-electron-donor) phosphinidene ligand, not detected. In contrast, the supermesitylphosphinidene complex undergoes a C(tBu)−H oxidative addition to the P atom under mild thermal conditions to give the phosphine derivative [Fe2Cp2(μ-CO)2(CO){PH(CH2CMe2)C6H2tBu2}], while its photolysis gave a mixture of the above phosphine complex and the phosphide−hydride derivatives cis- and trans-[Fe2Cp2(μ-H){μ-P(CH2CMe2)C6H2tBu2}(CO)2], the latter resulting from the oxidative addition of a P−H bond to the dimetal center.

Neutral and Cationic Alkylmanganese(II) Complexes Containing 2,6‐Bisiminopyridine Ligands

Manganese alkyl complexes stabilised by 2,6-bis(N,N'-2,6-diisopropyl-phenyl)acetaldiminopyridine ((iPr)BIP) have been selectively prepared by reacting suitable alkylmanganese(II) precursors, such as homoleptic dialkyls [(MnR(2))(n)] or the corresponding THF adducts [{MnR(2)(thf)}(2)] with the mentioned ligand. For R=CH(2)CMe(2)Ph or CH(2)Ph, formally Mn(I) derivatives are produced, in which one of the two R groups migrates to the 4-position of the central pyridine ring in the (iPr)BIP ligand. In contrast, a true dialkyl complex [MnR(2)((iPr)BIP)] can be isolated for R=CH(2)SiMe(3). In solution, this compound slowly evolves to the corresponding Mn(I) monoalkyl derivative. A detailed study of this reaction provides insights on its mechanism, showing that it proceeds through successive alkyl migrations, followed by spontaneous dehydrogenation. Protonation of [Mn(CH(2)SiMe(3))(2)((iPr)BIP)] with the pyridinium salt [H(Py)(2)][BAr'(4)] (Ar'=3,5-C(6)H(3)(CF(3))(2)) leads to the cationic species [Mn(CH(2)SiMe(3))(Py)((iPr)BIP)](+). Alternatively, the same complex can be produced by reaction of the pyridine complex [{Mn(CH(2)SiMe(3))(2)(Py)}(2)] with the protonated ligand salt [H(iPr)BIP](+)[BAr'(4)](-). This last reaction allows the synthesis of analogous cationic alkylmanganese(II) derivatives, when precursors of type [MnR(2)((iPr)BIP)] are not available. Treatment of these neutral and cationic (iPr)BIP alkylmanganese derivatives with a range of typical co-catalysts (modified methylaluminoxane (MMAO), B(C(6)F(5))(3), trimethyl or triisobutylaluminum) does not lead to active ethylene polymerisation catalysts.