External Catalyst Research Articles

Wavelength-Dependent Dynamic Behavior in Thiol-Ene Networks Based on Disulfide Exchange.

While latent catalysts have become a well-established strategy for locally and temporally controlling bond exchange reactions in dynamic polymer networks, there is a lack of inherently tailorable systems. Herein, we introduce a thiol-ene network based on disulfide exchange that alters its dynamic properties as a function of the color of light used during the curing reaction. For this purpose, selected allyl-bearing disulfides are synthesized, which are transparent at 450 nm but undergo disulfide scission upon 365 nm light irradiation, as confirmed by UV-vis and EPR measurements. Incorporated into a thiol-ene resin, the wavelength used in the curing reaction defines the dynamic properties of the obtained photopolymer. At 450 nm, photocuring yields a dynamic network with disulfide bonds, which relaxes to 63% of its original stress within 112 s at 160 °C (without the requirement of an external catalyst). In contrast, curing with 365 nm light induces disulfide scission yielding photopolymers, which contain predominately monosulfidic links. The permanent nature of the links effectively prevents relaxation of the polymer within a reasonable period of time, confirming the successful alteration of its dynamic properties simply by the color of the light source used.

Synergistic enhancement of nickel-cobalt nano-catalysts for 5-hydroxymethylfurfural conversion via electronic structure engineering and solar intensification

The electrooxidation of 5-hydroxymethylfurfural (HMF) into vital chemical intermediates has received widespread attention. In order to achieve efficient conversion of HMF, the main focus has been on the design and development of delicate catalysts. In addition, the introduction of an external field in the reaction process can also improve the electrocatalytic efficiency. In this paper, nickel-cobalt composite oxide catalysts with controlled metal centers (Ni/Co) were synthesized by a simple “coating-calcination” method. The rational rearrangement of d-electron by Co-doping facilitated the improvement of HMF adsorption, which was further confirmed by Density Functional Theory calculations. The catalysts synthesized at the optimal Co-doping ratio could still achieve 100 % of HMF conversion, 95.65 % of 2,5-furandicarboxylic acid yield, and 92.97 % of Faraday efficiency after 25 electrochemical cycles. Crucially, we introduced solar illumination to further enhance the performance of electrooxidation HMF. The catalyst performance was further improved via local photothermal effect and additional photocurrent. Therefore, the yield of FDCA was increased by more than 27 % under 2.0 kW m−2 illuminations. An electrooxidation system constructed based on external field enhancement and catalyst design provides new insights into the efficient conversion of biomass.

Dimethyl Sulfoxide Promoted Quinazolinone Synthesis

AbstractAn efficient and one‐step synthesis of quinazolinones using 2‐aminobenzamide and benzylamine in DMSO under external catalyst‐ and base‐free conditions is reported. A broad substrate scope and environment‐benign mild reaction conditions are the major attributes of this straightforward synthesis. Moreover, the synthesized quinazolinone derivatives were used to produce pharmaceutically active rutaecarpine analogues using a two‐step reaction: N‐alkylation followed by intramolecular cyclization.

Electrochemical N‐Centered Radical‐Triggered Intramolecular N−N Coupling for the Cyclization of o‐Aminyl Azobenzenes

AbstractAn electrochemical radical cyclization of o‐aminyl azobenzenes via N‐centered radical generation has been developed for the synthesis of benzotriazoles. The cyclization of o‐aminyl azobenzenes bearing a sulfonyl protection on amine readily proceeds in the absence of any external transition metal catalyst or chemical oxidant, and exhibits good tolerance towards functional groups.

Bis(2-butoxyethyl) Ether-Promoted O2-Mediated Oxidation of Alkyl Aromatics to Ketones under Clean Conditions.

Conventional oxidation processes for alkyl aromatics to ketones employ oxidants that tend to generate harmful byproducts and cause severe equipment corrosion, ultimately creating critical environmental problems. Thus, in this study, a practical, efficient, and green method was developed for the synthesis of aromatic ketones by applying a bis(2-butoxyethyl) ether/O2 system under external catalyst-, additive-, and base-free conditions. This O2-mediated oxidation system can tolerate various functional groups and is suitable for large-scale synthesis. Diverse target ketones were prepared under clean conditions in moderate-to-high yields. The late-stage functionalization of drug derivatives with the corresponding ketones and one-pot sequential chemical conversions to ketone downstream products further broaden the application prospects of this approach.

Analyzing the influence of the sustainability shift in European building codes on the alignment of identity, practice, and knowledge in commercial real estate firms

Sustainability has become a key concern across multiple sectors, including commercial real estate. Due to environmental challenges, numerous new European building regulations emphasize sustainability, pushing businesses to adapt. This research examines the effect of these sustainability-driven changes in European building codes on commercial real estate companies by utilizing the identity-practice-knowledge framework. Existing studies highlight external pressures and catalysts for change, while insights from seven interviews with industry experts reveal internal challenges, such as the need for additional expertise, and opportunities, such as enhancing sustainable practices. This paper explores how the shift in European building regulations impacts the alignment of identity, practice, and knowledge within commercial real estate firms and identifies the priorities these companies must address. The findings aim to assist these firms in preparing for the sustainability transition and in designing effective change processes for a seamless transformation.

Ionic liquid [TEMPOLQ8][HSO4] as oxidant cum solvent and catalyst for metal free tandem oxidative synthesis of quinazolin-4(3H)-ones

A new ionic liquid (IL), TEMPO-oxyoctylquinolinium hydrogen sulfate i.e., [TEMPOLQ8][HSO4] has been designed and reported for the first time as an efficient oxidant cum catalyst and solvent for one pot oxidative synthesis of quinazolin-4(3H)-ones from anthranilamide and benzyl alcohols. The reactions proceed to completion giving selectively quinazolin-4(3H)-ones in 6 hours at 120 °C eliminating the need for any external oxidant or transition metal catalysts. [TEMPOLQ8][HSO4] worked as an efficient catalyst cum oxidant and solvent for the oxidation of benzyl alcohols to benzaldehydes at 80 °C for 6 hours. This is the first report of controlled oxidation of benzyl alcohols to benzaldehydes under ionic liquid media in the absence of any external oxidant or catalyst. The in-situ generated aldehyde then couples with anthranilamide to afford the product. The protocol covers a wide substrate scope with access to potent medicinal drugs. Moreover, three gram-scale syntheses provide the synthetic utility of the protocol. The catalytic procedure was developed with green chemistry principles and its eco-friendliness was confirmed by its high eco-scale values. The IL was found to be more efficient compared to seven other newly synthesized ionic liquids used in the work.

Sulfur-containing cellulose esters for selectively anchoring gold for water catalytic decontamination

The facile preparation of sustainable sulfur-containing polymer functional materials has been obtained great attention due to their chemical reactivity and metal complexing ability. In this study, taking the solution properties advantages of the newly developed cellulose solvent system of DBU/DMSO/CO2, thiol and disulfide bond functionalized cellulose ester (TDSCE) was facilely prepared via in-situ tandem transesterification and oxidation reaction by using methyl 3-mercaptopropionate, without adding any external catalyst. The synthetic protocol was featured by that the DBU not only acted as reagent for the dissolution of cellulose, but also catalysts for the transesterification of cellulose with methyl 3-mercaptopropionate to yield cellulose 3-mercaptopropionate (Cell-MP) with maximum degrees of substitution (DS) of 0.77, and an oxidant for the partial oxidation of Cell-MP to produce a cellulose methyl 3,3′-disulfanediyldipropionate (Cell-MDSP) with maximum DS of 0.36 mixed ester, respectively. With successful introduction of thiol and disulfide bond into the cellulose backbone, the TDSCEs indicated desirable selective absorption of Au3+ from mimic heavy mental ions waste water due to the sulfur-Au chemistry with maximal adsorption capacity for Au3+ of 415.2 mg/g. The subsequent reduction of Au3+ into gold nanoparticles (Au NPs) fabricated a robust TDSCE-2@Au NPs composite catalyst with high catalytic activity for the hydrogenation treatment of water pollutes, such as 4-nitrophenol (4-NP)and azo dyes.

Oxidative Aminotrifluoromethylation of 1,4-Naphthoquinone.

A strategy for convenient and precise oxidative aminotrifluoromethylation of 1,4-naphthoquinone with the Togni reagent and amines has been demonstrated via a radical process. This method allows efficient access for the preparation of a wide range of CF3-functionalized 1,4-naphthoquinones under mild conditions, and its application in late-stage modification of drug molecules is achieved. Mechanistic studies indicate that 1,4-naphthoquinone serves as both a substrate and a catalyst and that the Togni reagent plays a dual role of a substrate and an oxidant. As a result, the title reaction can take place in the dark without external catalysts and oxidants.

Ammonia-Borane Dependent Transfer Hydrogenation of Carboxylic Esters to Primary Alcohols.

Here, we present a user-friendly protocol that uses bench-stable NH3·BH3 (AB) as the hydrogen transfer agent for the reduction of both aromatic and aliphatic esters without an external catalyst and base, delivering a structurally diverse array of primary alcohols (80-98% yields). The broad functional-group tolerance (halogen, boronic ester, -NO2, -OH, etc.) under environmentally acceptable conditions implies high practical utility. Further, a tandem catalytic conversion of a plastic waste polyethylene terephthalate (PET) bottle to 1,4-benzenedimethanol including fatty esters into respective fatty alcohols was shown.

HOO• as the Chain Carrier for the Autocatalytic Photooxidation of Benzylic Alcohols.

The oxidation of benzylic alcohols is an important transformation in modern organic synthesis. A plethora of photoredox protocols have been developed to achieve the aerobic oxidation of alcohols into carbonyls. Recently, several groups described that ultraviolet (UV) or purple light can initiate the aerobic oxidation of benzylic alcohols in the absence of an external catalyst, and depicted different mechanisms involving the photoinduction of •O2- as a critical reactive oxygen species (ROS). However, based on comprehensive mechanistic investigations, including control experiments, radical quenching experiments, EPR studies, UV-vis spectroscopy, kinetics studies, and density functional theory calculations (DFT), we elucidate here that HOO•, which is released via the H2O2 elimination of α-hydroxyl peroxyl radicals [ArCR(OH)OO•], serves as the real chain carrier for the autocatalytic photooxidation of benzylic alcohols. The mechanistic ambiguities depicted in the precedent literature are clarified, in terms of the crucial ROS and its evolution, the rate-limiting step, and the primary radical cascade. This work highlights the necessity of stricter mechanistic analyses on UV-driven oxidative reactions that involve aldehydes' (or ketones) generation.

Efficient eco-friendly synthesis of carbon nanotubes over graphite nanosheets from yellow corn: a one-step green approach

The present work reports the synthesis of multi-wall carbon nanotubes (MWCNTs) over graphite nanosheets by an easy and simple approach without using any external catalyst. Simply, yellow corn seeds were thermally annealed in a hydrogen atmosphere at 1050 °C for 3 h without any pretreatments. Notably, the growth of MWCNTs was observed to preferentially occur on the outer surface of the corn shell. This uncomplicated approach not only emphasizes the feasibility of synthesizing carbon nanomaterials using agricultural by-products but also underscores the potential applications of these synthesized materials in various fields. Samples were examined through a comprehensive analysis employing various techniques, including scanning electron microscopy (SEM), Raman spectroscopy, FTIR, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The findings unveiled the formation of rolled graphene accompanied by the presence of vertical multi-wall carbon nanotubes (MWCNTs) positioned over stacked graphene sheets. This detailed characterization provides insights into the structural features and arrangement of the synthesized materials, paving the way for a deeper understanding of their potential applications. The pyrolysis temperature is a crucial factor in the morphological characteristics of the synthesized carbon nanostructures. While graphene cage-like structures were obtained at 800 °C, small carbon nanotubes were grafted to larger ones and formed three-dimensional hierarchical morphologies when the annealing temperature increased to 900 °C. The growth mechanism of the carbon nanotubes was explained based on the jet self-extrusion of the generated gases through the inherent pores of the corn seeds. The current technique employed in manufacturing MWCNTs shows significant promise as a green synthesis method for producing catalyst-free MWCNTs suitable for industrial applications including sensors and energy storage materials.

Activation of peracetic acid by electrodes using biogenic electrons: A novel energy- and catalyst-free process to eliminate pharmaceuticals

Peracetic acid (PAA) has received increasing attention as an alternative oxidant for wastewater treatment. However, existing processes for PAA activation to generate reactive species typically require external energy input (e.g., electrically and UV-mediated activation) or catalysts (e.g., Co2+), inevitably increasing treatment costs or introducing potential new contaminants that necessitate additional removal. In this work, we developed a catalyst-free, self-sustaining bioelectrochemical approach within a two-chamber bioelectrochemical system (BES), where a cathode electrode in-situ activates PAA using renewable biogenic electrons generated by anodic exoelectrogens (e.g., Geobacter) degrading biodegradable organic matter (e.g., acetic acid) in wastewater at the anode. This innovative BES-PAA technique achieved 98 % and 81 % removal of 2 µM sulfamethoxazole (SMX) in two hours at pH 2 (cation exchange membrane) and pH 6 (bipolar membrane) using 100 μM PAA without external voltage. Mechanistic studies, including radical quenching, molecular probe validation, electron spin resonance (ESR) experiments, and density functional theory (DFT) calculations, revealed that SMX degradation was driven by reactive species generated via biogenic electron-mediated OO cleavage of PAA, with CH3C(O)OO• contributing 68.1 %, •OH of 18.4 %, and CH3C(O)O• of 9.4 %, where initial formation of •OH and CH3C(O)O• rapidly reacts with PAA to produce CH3C(O)OO•. The presence of common water constituents such as anions (e.g., Cl−, NO3−, and H2PO4−) and humic acid (HA) significantly hinders SMX removal via the BES-PAA technique, whereas CO32− and HCO3− ions have a comparatively minor impact. Additionally, the study investigated the removal of various pharmaceuticals present in secondary treated municipal wastewater, attributing differences in removal efficiency to the selective action of CH3C(O)OO•. This research demonstrates a novel PAA activation method that is ecologically benign, inexpensive, and capable of overcoming catalyst deactivation and secondary pollution issues.

Cover Picture

The cover image describes a novel and eco‐friendly electrochemical strategy for the electrochemical activation of trifluoromethyl thianthrenium triflate (TT–CF3+OTf−). The technique demonstrates successful trifluoromethylation of a diverse range of imidazole‐fused heteroaromatic compounds without the requirement of external oxidants or catalysts, aligning with the principles of green chemistry. More details are discussed in the article by Yu et al. on page 1679—1685.image

Acetal‐thiol Click‐like Reaction: Facile and Efficient Synthesis of Dynamic Dithioacetals and Recyclable Polydithioacetals

AbstractDithioacetals are heavily used in organic, material and medical chemistries, and exhibit huge potential to synthesize degradable or recyclable polymers. However, the current synthetic approaches of dithioacetals and polydithioacetals are overwhelmingly dependent on external catalysts and organic solvents. Herein, we disclose a catalyst‐ and solvent‐free acetal‐thiol click‐like reaction for synthesizing dithioacetals and polydithioacetals. High conversion, higher than acid catalytic acetal‐thiol reaction, can be achieved. High universality was confirmed by monitoring the reactions of linear and cyclic acetals (including renewable bio‐sourced furan‐acetal) with aliphatic and aromatic thiols, and the reaction mechanism of monomolecular nucleophilic substitution (SN1) and auto‐protonation (activation) by thiol was clarified by combining experiments and density functional theory computation. Subsequently, we utilize this reaction to synthesize readily recyclable polydithioacetals. By simple heating and stirring, linear polydithioacetals with w of ~110 kDa were synthesized from acetal and dithiol, and depolymerization into macrocyclic dithioacetal and repolymerization into polydithioacetal can be achieved; through reactive extrusion, a semi‐interpenetrating polymer dynamic network with excellent mechanical properties and continuous reprocessability was prepared from poly(vinyl butyral) and pentaerythritol tetrakis(3‐mercaptopropionate). This green and high‐efficient synthesis method for dithioacetals and polydithioacetals is beneficial to the sustainable development of chemistry.

Acetal-thiol Click-like Reaction: Facile and Efficient Synthesis of Dynamic Dithioacetals and Recyclable Polydithioacetals.

Dithioacetals are heavily used in organic, material and medical chemistries, and exhibit huge potential to synthesize degradable or recyclable polymers. However, the current synthetic approaches of dithioacetals and polydithioacetals are overwhelmingly dependent on external catalysts and organic solvents. Herein, we disclose a catalyst- and solvent-free acetal-thiol click-like reaction for synthesizing dithioacetals and polydithioacetals. High conversion, higher than acid catalytic acetal-thiol reaction, can be achieved. High universality was confirmed by monitoring the reactions of linear and cyclic acetals (including renewable bio-sourced furan-acetal) with aliphatic and aromatic thiols, and the reaction mechanism of monomolecular nucleophilic substitution (SN1) and auto-protonation (activation) by thiol was clarified by combining experiments and density functional theory computation. Subsequently, we utilize this reaction to synthesize readily recyclable polydithioacetals. By simple heating and stirring, linear polydithioacetals with w of ~110 kDa were synthesized from acetal and dithiol, and depolymerization into macrocyclic dithioacetal and repolymerization into polydithioacetal can be achieved; through reactive extrusion, a semi-interpenetrating polymer dynamic network with excellent mechanical properties and continuous reprocessability was prepared from poly(vinyl butyral) and pentaerythritol tetrakis(3-mercaptopropionate). This green and high-efficient synthesis method for dithioacetals and polydithioacetals is beneficial to the sustainable development of chemistry.

Transitions in Patristic Cosmology: From Cosmophobia to Universe-(Re)Making

The field of Patristics, or early Christian and Mediaeval Studies, traditionally works along the lines of historical and literary criticism. But this method is not always useful, especially when it comes to complex objects and circumstances. No wonder the current trend of replacing it, more often than not, by interdisciplinary frameworks. The article begins accordingly by reviewing three interdisciplinary frameworks, namely, the “socio-historical method”, “Deep Time”, and archaeological theorist Roland Fletcher’s “transitions”, highlighting their suitability for a comprehensive approach to Patristic cosmology. Here, cosmology should not be taken in the narrow sense of contemporary science. It means both a way of representing reality—a worldview—and a way of inhabiting the world. The present article analyses the evolution of the early Christian and mediaeval perception of the environment and the cosmos in Greek sources, pointing to successive transitions from apprehension (cosmophobia) to a keen interest in understanding nature to the thought that holiness represents a universe-(re)making agency. It addresses relevant historical and social circumstances, but proposes that the above transitions were triggered by internal or existential factors as well, and not only external, thus complementing Fletcher’s outline, which focuses upon external catalysts, such as economy and technology.

Adaptable Polyurethane Networks Containing Tertiary Amines as Intrinsic Bond Exchange Catalyst

AbstractVitrimers exhibit unique properties, such as thermal recyclability akin to thermoplastics, while structurally mirroring thermosets in terms of strength, durability, and chemical resistance. However, a significant limitation of these materials is their dependence on an external catalyst. Consequently, this research aims to develop vitrimer materials that incorporate an intrinsic catalyst, thus maintaining excellent thermomechanical properties and recyclability. Polyaddition polymerization is employed to synthesize the desired polymer, incorporating a self‐synthesized tertiary amine unit, (bis(2‐hydroxyethyl)‐3,3′‐((2‐(dimethylamino)ethyl)azanediyl)dipropanoate) (N‐diol), as an internal catalyst for transcarbamoylation and potential transesterification reactions. The resulting polymer, with a gel content of 97% and a glass transition temperature of 29 °C, is fabricated into test samples for comprehensive thermal and mechanical evaluations. The material demonstrates an initial Young's modulus of 555 MPa, retaining 81% of this value after two recycling processes. Additionally, using stress relaxation analysis (SRA), a topology freezing temperature of 82 °C, indicative of the characteristic Arrhenius‐like relaxation behavior, is identified with a bond exchange activation energy of 163 kJ mol−1.

Pyridinium‐Yne Click Polymerization: A Facile Strategy toward Functional Poly(Vinylpyridinium Salt)s with Multidrug‐Resistant Bacteria Killing Ability

AbstractPolymeric materials with antibacterial properties hold great promise for combating multidrug‐resistant bacteria, which pose a significant threat to public health. However, the synthesis of most antibacterial polymers typically involves complicated and time‐consuming procedures. In this study, we demonstrate a simple and efficient strategy for synthesizing functional poly(vinylpyridinium salt)s via pyridinium‐yne click polymerization. This click polymerization could proceed with high atom economy under mild conditions without any external catalyst, yielding soluble and thermally stable poly(vinylpyridinium salt)s with satisfactory molecular weights and well‐defined structures in excellent yields. Additionally, the incorporation of luminescent units such as fluorene, tetraphenylethylene, and triphenylamine into the polymer backbone confers excellent aggregation‐enhanced emission properties upon the resulting polymers, rendering them suitable for bacterial staining. Moreover, the existence of pyridinium salt imparts intrinsic antibacterial activity against multidrug‐resistant bacteria to the polymers, enabling them to effectively inhibit wound bacterial infection and significantly expedite the healing process. This work not only provides an efficient method to prepare antibacterial polymers, but also opens up the possibility of various applications of polymers in healthcare and other antibacterial fields.

Pyridinium-Yne Click Polymerization: A Facile Strategy toward Functional Poly(Vinylpyridinium Salt)s with Multidrug-Resistant Bacteria Killing Ability.

Polymeric materials with antibacterial properties hold great promise for combating multidrug-resistant bacteria, which pose a significant threat to public health. However, the synthesis of most antibacterial polymers typically involves complicated and time-consuming procedures. In this study, we demonstrate a simple and efficient strategy for synthesizing functional poly(vinylpyridinium salt)s via pyridinium-yne click polymerization. This click polymerization could proceed with high atom economy under mild conditions without any external catalyst, yielding soluble and thermally stable poly(vinylpyridinium salt)s with satisfactory molecular weights and well-defined structures in excellent yields. Additionally, the incorporation of luminescent units such as fluorene, tetraphenylethylene, and triphenylamine into the polymer backbone confers excellent aggregation-enhanced emission properties upon the resulting polymers, rendering them suitable for bacterial staining. Moreover, the existence of pyridinium salt imparts intrinsic antibacterial activity against multidrug-resistant bacteria to the polymers, enabling them to effectively inhibit wound bacterial infection and significantly expedite the healing process. This work not only provides an efficient method to prepare antibacterial polymers, but also opens up the possibility of various applications of polymers in healthcare and other antibacterial fields.