Self-coupling Reaction Research Articles

Interweavable Metalloporphyrin-based Fibers for Indirect Electrocatalysis.

The applications of indirect electrocatalysis toward potential industrial processes are drastically limited by the utilization or processing forms of electrocatalysts. The remaining challenges of electrocatalysts like the recycling in homogeneous systems or pulverization in heterogeneous systems call for advanced processing forms to meet the desired requirements. Here, we report a series of metalloporphyrin-based polymer fibers (M-PF, M = Ni, Cu and Zn) through a rigid-flexible polymerization strategy based on rigid metalloporphyrin and flexible thiourea units that can be applied as heterogenous redox-mediators in indirect electrocatalysis. These functional fibers with high strength and flexibility exhibit interweavable and designable functions that can be processed into different fiber-forms like knotted, two-spiral, three-ply, five-ply fibers or even interweaved networks. Interestingly, they can be readily applied in S-S bond cleaving/cyclization reaction or extended oxidative self-coupling reaction of thiols with high efficiency. Remarkably, it enables the scale-up production (1.25 g in a batch-experiment) under laboratory conditions.

Effects of quaternization sites and crossing methods on the slow-release and antibacterial effects of hydroxypropyltrimethyl ammonium chloride chitosan/dialdehyde chitosan-based film

In this study, the active food packaging film were prepared using hydroxypropyltrimethyl ammonium chloride chitosan with different substitution sites (O-HACC & N-HACC) and dialdehyde chitosan (DCS) grafted with protocatechuic acid (PA). To explore the effect of chitosan quaternization positions and crosslinking approaches on the slow-release and antibacterial properties, the double-crosslinked film were fabricated through the self-coupling reaction of PA and Schiff base reaction between amino groups on HACC and aldehyde groups on DCS. The HACC/DCS-based film exhibited stable porous three-dimensional networks with high nisin loading ratios (>90 %). With the participation of the catechol-catechol structure, the dense double-crosslinked film effectively restricted the diffusion of the water molecules, resulting in excellent slow-release properties fitting with the Korsmeyer-Peppas kinetic model. Especially, O-HACC/PA-g-DCS film, which had more reaction sites for Schiff base crosslinking than N-HACC, exhibited the equilibrium swelling ratio of 800 % at 60 h and could sustainably release nisin via non-Fickian diffusion behavior until 48 h. Moreover, the HACC/DCS-based double-crosslinked film performed good long-time antibacterial activity and preservation effects on salmon. On the 10th day of storage, the TVBN of N-HACC/PA-g-DCS and O-HACC/PA-g-DCS groups were only 28.26 ± 1.93 and 29.06 ± 1.68 mg/100 g and still lower than the thresholds.

Efficient Metal-Free Synthesis of Heterotriarylmethanes by 1,4-Addition of Benzofuran Azadienes

AbstractA novel and efficient method has been established for synthesizing a variety of heterotriarylmethanes with good yields by employing a metal-free self-coupling reaction of benzofuran azadienes. The involvement of t-BuONa is essential in this process. Remarkably, this technique boasts mild reaction conditions and exceptional compatibility with various functional groups, rendering it a versatile and invaluable asset in the realm of organic synthesis.

Plasmonic-mediated S[sbnd]C arylation and S[sbnd]S coupling on nanostructured silver electrodes monitored by in situ surface-enhanced Raman spectroscopy

Plasmon-mediated chemical reaction (PMCR) is a highly attractive field of research. Here we report in situ surface-enhanced Raman spectroscopic (SERS) monitoring of plasmonic-mediated SS bond-forming reaction. The reaction is thought to be a self-coupling reaction proceeding by photoinduced aromatic SC bond arylation. Surprisingly, the SC arylation and SS coupling are found to be occurred on both partially oxidized silver and silver nanoparticles. The results demonstrated that silver oxide or hydroxide and small molecule donor sacrifice agent played a crucial role in the reaction. This work facilitates the in-situ manipulation and characterization of the active silver electrode interface in conjunction with electrochemistry, and also establishes a promising new guideline for surface plasmon resonance photocatalytic reactions on metal nanostructures with high efficiency.

Highly efficient synthesis of imine activated by noble-metal-free CuInS2/C composite catalyst from MOFs under mild conditions

The self-coupling reaction of primary amines is an efficient method for obtaining imines, which are important components in the organic synthesis of medicines, pesticides, and fine chemical products. However, this reaction often requires the utilization of noble metals as catalysts to achieve high yields. Therefore, it is both desirable and challenging to explore efficient noble-metal-free catalysts. In this study, a composite catalyst of CuInS2/C with a regular octahedral shape and porous framework was synthesized using the HKUST-1 as precursor. The CuInS2/C catalyst exhibited effective catalytic activity in the self-coupling synthesis of imines under mild conditions, achieving a turnover frequency (TOF) of 105 h−1, which surpasses other non-noble metal catalysts. Mechanism investigations revealed that the excellent catalytic performance of CuInS2/C was attributed to its Cu(I) center and porous structure. The former generates radicals, while the latter enhances the transport of substrates and products, facilitating imine synthesis. Importantly, the CuInS2/C catalyst could be reused at least four times and applied in gram-scale experiments, demonstrating promising practical applications. This research presents a direct approach to developing noble-metal-free and highly efficient composite catalysts for imine synthesis using MOFs as precursors.

Selective N-monomethylation of amines using CO2/H2 catalyzed by high-activity Cu–ZrOx interface on SBA-15

N-methylation of amines using CO2 and H2 addresses the problems of expensive raw materials and harsh reaction conditions. However, designing a high-active and stable interface for the efficient preparation of monomethyl amine compounds in this tandem reaction remains a challenge to be overcome. Here, Cu–ZrOx composites are dispersed on SBA-15, silicalite-1, and ZSM-5 through the oxalic acid precipitation method for the N-methylation of amines using CO2 and H2. Results show that the dispersion of Cu–ZrOx on the surface of SBA-15 is superior to the other two molecular sieves and effectively prevents the sintering of active metals. A 20 wt% Cu–ZrOx/SBA-15 catalyst proves to be optimal for the N-methylation of aniline (AN) using CO2 and H2 to methylaniline (MA) and the catalyst performance remains stable after 5 cycle runs. The optimal catalyst exhibits an AN conversion of 97.6% and a selectivity of 96.5% for MA under the conditions of 180 °C, 4.0 MPa (H2/CO2/N2 = 72/24/4, molar ratio), and 8 h. Spectroscopic investigation and controlled experiments indicated that the preferential adsorbed AN on the catalyst surface reacts with CO2 to generate C–N bond, thereby avoiding the self-coupling side reaction of AN and achieving a high yield of 94.2% for MA.

Semiconductor nanosheets for electrocatalytic self-coupling of benzaldehyde to hydrobenzoin

The electrochemical reduction of biomass-derived feedstocks provides a sustainable platform for the synthesis of a wide range of chemical commodities and biofuels. Despite their interest, the optimization of reaction conditions, the screening of electrode materials, and the mechanistic understanding of these processes lag well behind other chemical routes. Here, we focus on the electrochemical self-coupling of benzaldehyde (BZH) to hydrobenzoin (HDB) using semiconductor electrocatalysts with nanosheet morphologies. By testing several semiconductor materials, a correlation is observed between their band gap and the electrochemical potential necessary to maximize selectivity towards HDB in alkaline medium, which we associate with the charge accumulation at the semiconductor surface. N-type CuInS2 provides the highest conversion rate at 0.3 mmol cm−2h−1 with a selectivity of 98.5 % at −1.3 V vs. Hg/HgO. Additional density functional theory calculations demonstrate a lower kinetic energy barrier at the CuInS2 surface compared with graphitic carbon, proving its catalytic role in the self-coupling reaction of BZH.

Back Cover: Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag−ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry (Angew. Chem. Int. Ed. 32/2023)

A novel method based on in situ synchrotron radiation photoionization mass spectrometry has been developed to capture the nascent intermediates during photocatalytic methane oxidation over Ag-ZnO. The results shed light on the overoxidation and self-coupling reaction mechanism of •CH3, as described by Chengyuan Liu, Yang Pan et al. in their Research Article (e202304352).

Rücktitelbild: Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag−ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry (Angew. Chem. 32/2023)

A novel method based on in situ synchrotron radiation photoionization mass spectrometry has been developed to capture the nascent intermediates during photocatalytic methane oxidation over Ag-ZnO. The results shed light on the overoxidation and self-coupling reaction mechanism of •CH3, as described by Chengyuan Liu, Yang Pan et al. in their Research Article (e202304352).

Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag-ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry.

Photocatalysis has emerged as an ideal method for the direct activation and conversion of methane under mild conditions. In this reaction, methyl radical (⋅CH3 ) was deemed a key intermediate that affected the yields and selectivity of the products. However, direct observation of ⋅CH3 and other intermediates is still challenging. Here, a rectangular photocatalytic reactor coupled with in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) was developed to detect reactive intermediates within several hundred microseconds during photocatalytic methane oxidation over Ag-ZnO. Gas phase ⋅CH3 generated by photogenerated holes (O- ) was directly observed, and its formation was demonstrated to be significantly enhanced by coadsorbed oxygen molecules. Methoxy radical (CH3 O⋅) and formaldehyde (HCHO) were confirmed to be key C1 intermediates in photocatalytic methane overoxidation to CO2 . The gas-phase self-coupling reaction of ⋅CH3 contributes to the formation of ethane, which indicates the key role of ⋅CH3 desorption in the highly selective synthesis of ethane. Based on the observed intermediates, the reaction network initiated from ⋅CH3 of photocatalytic methane oxidation could be clearly illustrated, which is helpful for studying the photocatalytic methane conversion processes.

Design and electrochemical study of merocyanine dyes: Influence of substituents on the redox behaviors and fouling propensity at ubiquitous electrode surfaces

Investigations into the electrochemical behaviours of merocyanine dyes containing the N-methylbenzothiazolium (Btz) acceptor vinyl linked to phenolic (PhO) donors with electron-donating substituents (chlorine atoms), electron-withdrawing substituents (methoxy groups), or without any substituents at their ortho positions on common glassy carbon electrodes (GCEs), as well as gold and platinum surfaces were performed. It was found that the sensing signals and fouling propensities were heavily dependent on the electrode being used. The inclusion of substituent functional groups also minimized the electrochemical fouling of the dyes and further affected the electron transfer kinetics. The reaction mechanisms of the dyes were examined using electrochemical analysis and DFT computations. For both the Cl2PhOBtz and OMe2PhOBtz (Scheme 1), the radical species underwent a partial rearrangement to form radical species in the ortho position following the loss of the first electron. Following the first electron loss for the PhOBtz (Scheme 1), the formed radical species was unstable and underwent an instantaneous self-coupling reaction with a similar radical species to produce diquinone methide. This resulted in an irreversible oxidation reaction and increased the fouling propensity of the formed species on the electrodes. By understanding the influences of various substituents and taking into consideration of the fouling propensities, reversibility and sensing signals with respect to specific surfaces, novel aptamer-binding merocyanine dyes may be designed and synthesized for the development of highly robust and sensitive electrochemical sensors for medical and environmental applications.

Synthesis of graphdiyne on a copper substrate via a self-coupling reaction.

A new strategy is proposed to prepare graphdiyne via the self-coupling reaction of hexakis(bromoethynyl)benzene (hBEP) with alkynyl bromide groups. Prominently, the reaction can proceed moderately in 12 h at room temperature. The as-synthesized film displays a porous structure, excellent chemical characteristics, and an admirable catalytic performance for the hydrogen/oxygen evolution reaction (HER/OER).

Mixed oxidation of chlorophene and 4-tert-butylphenol by ferrate(VI): Reaction kinetics, cross-coupling products and improved utilization efficiency of ferrate(VI)

As two representative phenolic pollutants, chlorophene (CP) and 4-tert-butylphenol (4-tBP) are used in large quantities and could have adverse effects on aquatic organisms and even human health. Due to their co-occurrence in water and wastewater, the oxidative degradation of mixed solution of the two phenols by ferrate (Fe(VI)) was systematically investigated in this work. Compared with the single solution, the kapp values of CP and 4-tBP were increased by 15.7% and 91.9%, respectively in the mixed solution, and the calculated reaction stoichiometric efficiency (RSE) was also improved by more than one time. The reaction intermediates were identified by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis, from which three possible pathways including direct oxidation, oxygen transfer, ring opening and coupling reaction were proposed for mixed transformation of CP and 4-tBP in Fe(VI) system. The single/double oxygen transfer and single-electron transfer mechanism for the corresponding formation of hydroxylation products and coupling products from CP and 4-tBP were further elucidated by density functional theory (DFT) calculations. Since the cross-coupling reaction was more prone to occur than self-coupling reaction, the addition of another phenol promoted the conversion of the original phenol, leading to the increased kapp values of the two phenols in mixture solution. Finally, the salt bridge experiment also confirmed that the electron transfer between organic pollutants and Fe(VI) was enhanced in mixture solution of phenols. Findings of this study may provide useful information for eliminating co-existing water contaminants by Fe(VI).

Self-coupling reactions of terminal alkynes catalyzed by nanorod-like metalloporphyrin organic frameworks encapsulated with copper nanoparticles: Synergistic catalytic effects of dual copper structures

By encapsulating metal nanoparticles (NPs), the synergistic effect between the metalloporphyrins and the metal nanoparticles in metalloporphyrin organic frameworks (P-MOFs) can boost its catalytic performance. The self-coupling reaction of terminal alkynes is a kind of important organic reaction and can take place with the aid of the catalyst. A nanorod-like metal-organic skeleton PCN-222(Cu) with carboxy porphyrins as ligands was synthesized as the precursor. By a double-solvent approach, the composite catalysts with varying copper nano-loadings in PCN-222(Cu) pores were obtained. Among them, 1.9 wt% of Cu NPs in Cu@PCN-222(Cu) has excellent catalytic activity and stability for the self-coupling reaction of terminal alkynes. PCN-222(Cu) can stabilize the Cu NPs, control the size selectivity and crystal form. The copper porphyrins and Cu NPs in Cu@PCN-222(Cu) both serve as the catalytic active sites. This strategy, which using porphyrin-structured MOFs to construct dual active sites with the same element, has promising applications in MOFs catalysis.

Expanded Azaporphyrins Consisting of Multiple BODIPY Units: Global Aromaticity and High Affinities Towards Alkali Metal Ions.

The one-pot self-coupling reaction of 3-amino-5-bromo-BODIPY 9 under Buchwald-Hartwig amination conditions gave nitrogen-bridged cyclic BODIPY tetramer 10, pentamer 11, and hexamer 12. Oxidation of 10, 11, and 12 in the presence of alkali metal ions provided 13, 15, and 16, respectively, as the first examples of expanded azaporphyrins possessing more than six pyrrole rings. Curiously, the oxidation even in the absence of alkali metal ions gave the same complexes as a result of spontaneous complexation. 10-12 showed large association constants (104 -106 M-1 ) with K+ and Na+ , but the spontaneous complexations were not observed, indicating the extremely high affinities of 13-16 toward alkali metal ions, which can be ascribed to the multiple and effective ion-dipole interaction of the alkali metal ion with the negatively polarized F atoms of the BF2 walls surrounding the cavity. Importantly, 13, 14, and 15 show diatropic ring currents as a result of global aromaticity.

Detachable all-carbon-linked 3D covalent organic framework films for semiconductor/COF heterojunctions by continuous flow synthesis

Detachable all-carbon-linked 3D covalent organic framework films for semiconductor/COF heterojunctions by continuous flow synthesis

Degradation of novel mineral flotation reagent 8-hydroxyquinoline by superparamagnetic immobilized laccase: Effect, mechanism and toxicity evaluation

• The effect of main constituents of MPW on 8-HQ degradation was evaluated. • Favorable 8-HQ degradation efficiency was achieved in real lead–zinc mine water. • The biocatalyst exhibited efficient recyclability and reusability. • Degradation predominantly generated various structural 8-HQ oligomers/polymers. • TOC and toxicity were effectively reduced with the degradation of 8-HQ. The environmental impact of the mining industry requires efficient and eco-friendly technologies to mitigate the presence of mineral flotation reagents (MFRs) in mineral processing wastewater (MPW) prior to their discharge into the environment. In this work, for the first time, a robust, easily separable and reusable biocatalyst, Fe 3 O 4 @SiO 2 -NH 2 -Lac, was used for the degradation of a novel mineral flotation reagent 8-hydroxyquinoline (8-HQ). Under optimized conditions, Fe 3 O 4 @SiO 2 -NH 2 -Lac achieved 89.2% 8-HQ degradation efficiency within 6 h. The effect of the main constituents of MPW on 8-HQ degradation, including metal ions, organic solvents, surfactant, metal chelator and flotation frother was evaluated. The Fe 3 O 4 @SiO 2 -NH 2 -Lac also displayed favorable degradation efficiency of 8-HQ in real lead–zinc mine water. The biocatalyst could be easily recovered and had a satisfactory reusability, retaining 64.5% of 8-HQ degradation efficiency in the sixth reaction cycle. Identification of intermediate products revealed that Fe 3 O 4 @SiO 2 -NH 2 -Lac mediated reaction predominantly generated various structural 8-HQ oligomers/polymers. A potential degradation pathway for 8-HQ was speculated as follows: Fe 3 O 4 @SiO 2 -NH 2 -Lac initially catalyzed the oxidation of 8-HQ to yield the corresponding reactive radical intermediates, which subsequently undergone self-coupling reaction via C − C and C − O − C covalent coupling at their ortho and/or para positions, finally forming oligomers and polymers. The inhibition assays of marine bacterium ( Vibrio fischeri ) demonstrated that the toxicity of 8-HQ and its intermediate products was effectively reduced after Fe 3 O 4 @SiO 2 -NH 2 -Lac treatment. The results of this study might present an alternative immobilized laccase-based clean biotechnology for the clean-up and detoxification of 8-HQ contaminated MPW.

Effect of Reaction Conditions on the Conversion and Selectivity of MCM-41 and Al-20-MCM-41 Catalyzed Amine Coupling Reactions

The study has been performed to examine the effect of different reaction conditions (presence of a solvent, absence of solvent, presence of air and closed vessel with an absence of air) on the conversion and selectivity of oxidative coupling reactions of amines to imines using MCM-41 and Al-20-MCM- 41 catalysts. Two types of coupling reactions were discussed viz. self-coupling and cross coupling. Self-coupling reaction was observed to be faster with Al-20-MCM-41 than MCM-41, while the cross-coupling reactions with Al-20-MCM-41 was slightly slower than MCM-41. The conversion and selectivity of self and cross coupling reactions in different reaction conditions were also investigated. The reaction was found to be of shifting order, initially first order when amine concentration was high and tending towards zero at lower amine concentration. It was evident that both catalysts Al-20-MCM-41 and MCM-41 showed a good catalytic activity on the oxidative coupling reactions of amine but somewhat higher conversion was obtained with Al-20-MCM-41 because of presence of acidic site.

Optimizing bromide anchors for easy tethering of amines, nitriles and thiols in porous organic polymers towards enhanced CO2 capture

Porous organic polymers with labile leaving groups offer direct access to reactive functional groups, otherwise not permissible during network formation. In a one-step, open air, self-coupling reaction of tris bromomethyl benzene, we report highly porous, bromine rich C–C bonded porous polymers. Due to the steric nature of the monomer, restrictive crosslinking allowed pendent bromine groups to remain unreacted and provided rapid exchange into amines, nitriles, and thiols. This simple but powerful strategy yielded two isostructural but varying porosity and pendent group density polymers, allowing a comparative gas uptake study. Despite having lower surface area, the porous polymer formed at low temperature showed higher amination due to higher density of bromine groups. The polymers with more pendant groups resulted better CO 2 uptake performances than higher porosity polymers with less pendant groups. Although post-modification decreased surface area of materials, amine functionalization greatly improved the CO 2 uptake capacity. The ethylenediamine appended version exhibited 4.7 times increase in CO 2 uptake capacity with highest CO 2 /N 2 selectivity of 729 (298 K), and with an isosteric heat of 97 kJ mol −1 at zero coverage. • The one-step synthesis of bromine tethered C–C bonded nanoporous polymers. • The tuning of porosity and number of bromine anchors by changing reaction temperature. • Successful tailoring of benzyl bromides with amine, thiol, and nitrile moieties. • The density of surface functional groups exhibits higher impact on CO 2 adsorption performance than porosity.

Insights into the Electron-Transfer Mechanism of Permanganate Activation by Graphite for Enhanced Oxidation of Sulfamethoxazole.

Many reagents as electron sacrificers have been recently investigated to induce decomposition of permanganate (KMnO4) to produce highly reactive intermediate Mn species toward oxidation of organic contaminants; however, this strategy meanwhile causes low KMnO4 utilization efficiency. This study surprisingly found that graphite can mediate direct electron transfer from organics (e.g., sulfamethoxazole (SMX)) to KMnO4, resulting in high KMnO4 utilization efficiency, rather than reductive sites of graphite-induced conversion of KMnO4 to highly reactive intermediate Mn species. The galvanic oxidation process (GOP) and comparative experiments of different organic contaminants prove that the KMnO4/graphite system mainly extracts electrons from organic contaminants via a one-electron pathway instead of a two-electron pathway. More importantly, the KMnO4/graphite system has superior reusability, graphite can keep a long-lasting reactivity, and the KMnO4 utilization efficiency elevates significantly after each cycle of graphite. The transformation of SMX in the KMnO4/graphite system mainly includes self-coupling, hydroxylation, oxidation, and hydrolytic reaction. The work will improve insights into the electron-transfer mechanism and unveil the advantages of efficient KMnO4 utilization in the KMnO4-based technologies in environmental remediation.