Monthly Archives: September 2023

An Unexpected Synthesis of Crowded Triphenylenes

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An Unexpected Synthesis of Crowded Triphenylenes

Reaction of 2,5-dibromothiophene dioxide with two equivalents of tetracyclone yields a heptaphenyl triphenylene, presumably by double Diels-Alder addition followed by fragmentation and rearrangement of the resulting radicals.


Abstract

In attempts to make octaphenyldibenzofuran (7) and octaphenyldibenzothiophene (8), 2,5-dibromofuran (4) and 2,5-dibromothiophene (5), respectively, were heated with tetracyclone (2) under forcing conditions, but only single addition products, such as 2-bromo-4,5,6,7-tetraphenylbenzofuran (10) and 2-bromo-4,5,6,7-tetraphenylbenzothiophene (12) were observed. However, when 2,5-dibromothiophene-1,1-dioxide (6) was heated with tetracyclone, the chief product was 1,2,3,4,6,7,8-heptaphenyltriphenylene (14). Similarly, when compound 6 was heated with acecyclone (15), the product was 11,18,20-triphenyldiacenaphtho[a,h]triphenylene (16). Both 14 and 16 have been characterized by X-ray crystallography. They are proposed to form from double Diels-Alder addition products of the cyclopentadienones by extrusion of sulfur dioxide and rearrangement of the resulting radicals.

Second‐Generation Total Synthesis of the Pigment Aurantricholone

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Second-Generation Total Synthesis of the Pigment Aurantricholone

Previously, 6,6-dimethoxy-6,7-dihydrobenzocyclohepten-5-ones (“ketoketals”) gained by ring-closing metatheses (“RCMs”) gave 6-hydroxybenzocyclohepten-5-ones (“benzotropolones”) by hydrolyses with 10 equiv. of hot TsOH. Now, an RCM-based ketoketal allowed to reach the benzotropolone aurantricholone by total synthesis for the second time and to avoid a forcing hydrolysis. Another key to success was establishing the pulvinone(−like) motifs by our recently developed Suzuki strategy.


Abstract

Our first total synthesis of aurantricholone established its benzotropolone core by the ring-enlargement of a tetralone. Here we describe another total synthesis of aurantricholone. It reaches the benzotropolone core from a known olefin metathesis product via an equally known dibromide, both of which contain a ketoketal moiety. The next transformation - step 9 overall - engaged this motif in a β-elimination of ROH rather than in a hydrolysis under the forcing acidic conditions indispensable in all prior benzotropolone preparations from such an intermediate. In step 10, the C sp2−Br bonds of the elimination product underwent two doubly Z-selective Suzuki couplings with a boronylated O-methyl 4-methylidenetetronate. This gave penta(O-methyl)aurantricholone. Its NMR shifts matched essentially those of a derivative of natural aurantricholone by Steglich et al. Three O−Me bonds were cleaved with BBr3/CH2Cl2 (step 11) and two O−Me bonds with LiBr/DMF (step 12). A 1 : 3 co-crystal of aurantricholone and DMSO allowed for an X-ray structure analysis.

Organic Molecule Bifunctionalized Polymeric Carbon Nitride for Enhanced Photocatalytic Hydrogen Peroxide Production

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Organic Molecule Bifunctionalized Polymeric Carbon Nitride for Enhanced Photocatalytic Hydrogen Peroxide Production

Organic molecule bifunctionalized polymeric carbon nitride (MBCN) with edge-grafted and interchain-embedded benzene rings as the respective electron-donating group and charge-transfer channel exhibits significantly enhanced photocatalytic H2O2 production activity due to the promoted separation/transfer of photogenerated charge carriers and visible light absorbance. Based on density functional theory calculation and experimental results, we propose the transfer path of photogenerated electrons.


Abstract

Modifying the polymeric carbon nitride (CN) with organic molecules is a promising strategy to enhance the photocatalytic activity. However, most previously reported works show that interchain embedding and edge grafting of the organic molecule can hardly be achieved simultaneously. Herein, we successfully synthesized organic molecule bifunctionalized CN (MBCN) through copolymerization of melon and sulfanilamide at a purposely elevated temperature of 550 °C. In MBCN, the edge grafted and interchain embedded benzene rings act as the electron-donating group and charge-transfer channel, respectively, rendering efficient photocatalytic H2O2 production. The optimal MBCN exhibits a significantly improved non-sacrificial photocatalytic H2O2 generation rate (54.0 μmol g−1 h−1) from pure water, which is 10.4 times that of pristine CN. Experimental and density functional theory (DFT) calculation results reveal that the enhanced H2O2 production activity of MBCN is mainly attributed to the improved photogenerated charge separation/transfer and decreased formation energy barrier (▵G) from O2− to the intermediate 1,4-endoperoxide (⋅OOH). This work suggests that simultaneous formation of electron donating group and charge transfer channel via organic molecule bifunctionalization is a feasible strategy for boosting the photocatalytic activity of CN.

Enantioselective Construction of Axially Iodobenzocarbazole Derivatives by Stereogenic‐at‐Cobalt(III)‐Complex‐Catalyzed Iodoarylation of Alkynes

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Enantioselective Construction of Axially Iodobenzocarbazole Derivatives by Stereogenic-at-Cobalt(III)-Complex-Catalyzed Iodoarylation of Alkynes

A direct protocol for the facile construction of axially chiral iodobenzocarbazole derivatives via the catalytic asymmetric iodocyclization of indole moiety linked alkynes, using stereogenic-at-cobalt(III)-complex as the catalyst, has been developed. A range of versatile axially chiral iodobenzocarbazoles were obtained with up to 98 % ee under mild conditions.


Abstract

A new synthetic approach to novel axially chiral iodobenzocarbazole derivatives based on the highly enantioselective intramolecular iodoarylation of linked alkyne-indole systems was developed by using the versatile chiral catalyst, stereogenic-at-cobalt(III)-complex, through an axially chiral iodinated vinylidene o-quinone methide (IVQM) intermediate. This protocol provides 21 examples in excellent yields with good to high enantioselectivities (up to 96 % yield, 98 % ee). Furthermore, the introduced iodine atoms can easily be converted into other functional groups.

Quantifying the Resistive Losses of the Catalytic Layers in Anion‐Exchange Membrane Fuel Cells

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Quantifying the Resistive Losses of the Catalytic Layers in Anion-Exchange Membrane Fuel Cells

An operando anion-exchange membrane fuel cell (AEMFC) was analyzed via artificial intelligence. Using impedance spectroscopy genetic programming (ISGP), we quantified the resistances of the various physical processes occurring in the system for the first time providing valuable information to the AEMFC community with wider applicability to other electrochemical process.


Abstract

The existing gap in the ability to quantify the impacts of resistive losses on the performance of anion-exchange membrane fuel cells (AEMFCs) during the lifetime of their operation is a serious concern for the technology. In this paper, we analyzed the ohmic region of an operating AEMFC fed with pure oxygen followed by CO2-free air at various operating currents, using a combination of electrochemical impedance spectroscopy (EIS) and a novel technique called impedance spectroscopy genetic programming (ISGP). Presented here for the first time in this work, we isolated and quantified the individual effective resistance (Reff) values occurring in the AEMFC and their influence on performance as operating conditions change. We believe that this first work is vital to help distinguish the influence of the individual catalytic and mass-transfer processes in this technology thereby providing valuable data to the AEMFC community, with potentially wider applicability to other electrochemical devices where individual physical processes occur simultaneously and need to be sequestered for deeper understanding.

Effects of Charged Surfactants on Interfacial Water Structure and Macroscopic Properties of the Air‐Water Interface

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Effects of Charged Surfactants on Interfacial Water Structure and Macroscopic Properties of the Air-Water Interface

Surfactants significantly influence the air-water interfacial properties, yet their connection with the surfactant molecular structure remains unclear. Combining simulations and experiments to explore the molecular arrangement of SDS and DTAB surfactants at the air-water interface reveals noteworthy findings, which offer valuable insights into the influence of surfactants on the macroscopic behaviour of aqueous foams and foaming solutions, particularly the foamability and foam stability.


Abstract

Surfactants are used to control the macroscopic properties of the air-water interface. However, the link between the surfactant molecular structure and the macroscopic properties remains unclear. Using sum-frequency generation spectroscopy and molecular dynamics simulations, two ionic surfactants (dodecyl trimethylammonium bromide, DTAB, and sodium dodecyl sulphate, SDS) with the same carbon chain lengths and charge magnitude (but different signs) of head groups interact and reorient interfacial water molecules differently. DTAB forms a thicker but sparser interfacial layer than SDS. It is due to the deep penetration into the adsorption zone of Br− counterions compared to smaller Na+ ones, and also due to the flip-flop orientation of water molecules. SDS alters two distinctive interfacial water layers into a layer where H+ points to the air, forming strong hydrogen bonding with the sulphate headgroup. In contrast, only weaker dipole-dipole interactions with the DTAB headgroup are formed as they reorient water molecules with H+ point down to the aqueous phase. Hence, with more molecules adsorbed at the interface, SDS builds up a higher interfacial pressure than DTAB, producing lower surface tension and higher foam stability at a similar bulk concentration. Our findings offer improved knowledge for understanding various processes in the industry and nature.

Formal Radical Deoxyfluorination of Oxalate‐Activated Alcohols Triggered by the Selectfluor‐DMAP Charge‐Transfer Complex

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Formal Radical Deoxyfluorination of Oxalate-Activated Alcohols Triggered by the Selectfluor-DMAP Charge-Transfer Complex

In this work, a photon- and metal-free approach for the radical fluorination of aliphatic oxalate-activated alcohols is reported.


Abstract

We present a photon- and metal-free approach for the radical fluorination of aliphatic oxalate-activated alcohols. The method relies on the spontaneous generation of the N-(chloromethyl)triethylenediamine radical dication, a potent single electron oxidant, from Selectfluor and 4-(dimethylamino)pyridine. The protocol is easily scalable and provides the desired fluorinated products within only a few minutes reaction time.

From a Batch to a Continuous Supported Ionic Liquid Phase (SILP) Process: Anhydrous Synthesis of Oxymethylene Dimethyl Ethers

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From a Batch to a Continuous Supported Ionic Liquid Phase (SILP) Process: Anhydrous Synthesis of Oxymethylene Dimethyl Ethers

Continuous OME n Synthesis: Supported ionic liquid phase (SILP)-catalysts open the tap for the novel continuous and anhydrous synthesis of oxymethylene dimethyl ethers (OME n ) by reaction of dimethoxymethane (OME1) with molecular gaseous formaldehyde (FA) as catalyzed by M[NTf2] x salts, most favorably for M=Cu+, Co2+ and Mg2+.


Abstract

Oxymethylene dimethyl ethers (OME n ; CH3(−OCH2) n −OCH3) are promising sustainable synthetic fuels when produced from CO2 and green H2. The synthesis pathway presented here overcomes synthetic problems and includes the reaction of dimethoxymethane (OME1) with molecular gaseous formaldehyde in a novel continuous, anhydrous reaction setup. An initially performed wide batch-catalyst screening highlighted the salts M[NTf2] x with M=Cu+, Co2+ and Mg2+ as especially interesting catalysts (NTf2=N(SO2CF3)2). Supported ionic liquid phase (SILP)-catalysts were prepared on this basis and demonstrated the successful synthesis of OME n in a continuous process. The SILP-catalysts immobilized in the IL EMIM[BF4] showed a fast and strong deactivation, but those with the IL EMIM[NTf2] showed excellent catalytic performance and stable results in continuous operations exceeding 19 h. The influence of the weight hourly space velocity (WHSV), the reaction temperature as well as the storage conditions of the catalysts (inert vs non-inert) were investigated. 90 °C was identified as ideal reaction temperature. High feed-gas flows (WHSV=15.8 h−1) are preferable in terms of product selectivity S OME2-5>90 mol- % with an OME1 conversion X OME1=5.10 mol- % at the same time. We also demonstrated that the catalysts can be stored in air for 50 days without loss of activity. The SILP-catalysts were analyzed by NMR and IR spectroscopy. Furthermore, the thermodynamics of the reaction mechanism of some selected catalysts was calculated by DFT theory to this reaction.

Preparation of 3‐D Porous Pure Al Electrode for Al‐Air Battery Anode and Comparison of its Electrochemical Performance with a Smooth Surface Electrode

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Preparation of 3-D Porous Pure Al Electrode for Al-Air Battery Anode and Comparison of its Electrochemical Performance with a Smooth Surface Electrode

The Cover Feature shows the Al-air battery test cell prepared for the 3D Al-porous electrode. There are also clues about the reaction on the porous electrode surface in contact with the solution. Porous electrodes can positively affect battery performance by providing additional active surface area in NaOH solution. The battery performance of the electrodes is analyzed in comparison with a smooth surface electrode. Cover design by Osman Kahveci. More information can be found in the Research Article by O. Kahveci.


Electrochemical Nitrate Reduction to Ammonia – Recent Progress

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Electrochemical Nitrate Reduction to Ammonia – Recent Progress

This work provides a comprehensive review of the current progress on the mechanism, influencing factors, product detection methods, performance evaluation methods and strategies used to design efficient electrocatalysts for the electrochemical synthesis of ammonia from nitrate. Additionally, it briefly predicts the future research direction with the aim of offering a certain reference for the development of green and environmentally friendly nitrogen fixation technology.


Abstract

The presence of nitrate in industrial, domestic and agricultural wastewater has a detrimental impact on both ecosystem and human health, as remediation and purification efforts are slow, challenging and difficult, given the high solubility and stability of this pollutant. Taking nitrate into high value-added ammonia by electrochemical reduction can overcome high pollution and energy consumption limit of Haber-Bosch process with long-term significance of environmental protection and energy saving. This review summarized the research progress on the electrocatalytic reduction of nitrate to ammonia, with a focus on the reaction mechanisms, influencing factors, product detection methods, performance evaluation methods and the research status of electrocatalysts up to now. The review reported the latest strategies employed to design efficient electrocatalysts, such as pore structure regulation, alloying, heterostructure construction, defect and interface engineering, crystal surface regulation and microenvironment modulation of single-atom catalysts. It highlights critical factors that determin the performance in terms of nitrate adsorption, exposed active sites, mass transfer rate, intermediates barrier and side reactions, as well as the stability of electrocatalysts and recovery of ammonia. In addition, the future direction of technology for electrocatalytic reduction of nitrate to ammonia has also been proposed.