Reaction Of Ethers Research Articles

Investigation of Gelation Techniques for the Fabrication of Cellulose Aerogels.

Because of the pronounced degradation of the environment, there has been an escalated demand for the fabrication of eco-friendly and highly efficient products derived from renewable sources. Cellulose aerogels have attracted significant interest attributable to their structural characteristics coupled with biodegradability and biocompatibility. The features of the molecular structure of cellulose allow for the use of various methods in the production of gels. For instance, the presence of hydroxyl groups on the cellulose surface allows for chemical crosslinking via etherification reactions. On the other hand, cellulose gel can be procured by modulating the solvent power of the solvent. In this study, we investigate the impact of the gelation methodology on the structural attributes of aerogels. We present methodologies for aerogel synthesis employing three distinct gelation techniques: chemical crosslinking, cryotropic gelation, and CO2-induced gelation. The outcomes encompass data derived from helium pycnometry, Fourier-transform infrared spectroscopy, nitrogen porosimetry, and scanning electron microscopy. The resultant specimens exhibited a mesoporous fibrous structure. It was discerned that specimens generated through cryotropic gelation and CO2-induced gelation manifested higher porosity (93-95%) and specific surface areas (199-413 m2/g) in contrast to those produced via chemical crosslinking (porosity 72-95% and specific surface area 25-133 m2/g). Hence, this research underscores the feasibility of producing cellulose-based aerogels with enhanced characteristics, circumventing the necessity of employing toxic cross-linking agents. The process of gel formation through chemical crosslinking enables the creation of gels with enhanced mechanical properties and a more resilient structure. Two alternative methodologies prove particularly advantageous in applications necessitating biocompatibility and high porosity. Notably, CO2-induced gelation has not been hitherto addressed in the literature as a means to produce cellulose gels. The distinctive feature of this approach resides in the ability to combine the stages of obtaining an aerogel in one apparatus.

Amphiphilic HZSM-5 for Cyclopentene Hydration at the Liquid-Liquid Interface in Pickering Emulsion.

Zeolite is considered an ideal catalyst for olefin hydration due to its high specific surface area and abundant acid sites. However, the immiscibility of the water-oil two phases in olefin hydration limits mass transfer, and the side reaction of etherification occurs acutely, resulting in a low yield of alcohol. Thus, water-oil amphiphilic HZSM-5 was prepared by sulfonating silanized zeolite. The successful introduction of organic and sulfonic acid groups is demonstrated by FT-IR, TG, and water contact angles. Amphiphilic HZSM-5 can stabilize the Pickering emulsion and catalyze cyclopentene hydration at the phase interface. In addition, NH3-TPD and Py-IR show that the amount of strong Bro̷nsted acid sites of zeolites increases significantly after sulfonation. This facilitates the rate-determining step of cyclopentene activation by H+ to form carbocation. Moreover, the nucleophilic side reactions are inhibited by a high concentration of H+. Finally, under the optimized reaction condition, the conversion of cyclopentene can achieve 5.066% with a selectivity of 85.37% to cyclopentanol, which almost reaches the reaction equilibrium.

Eco-Friendly Homo- and Cross-Etherification of Benzyl Alcohols Catalyzed by Iron(II/III) Chloride in Propylene Carbonate as a Green and Recyclable Solvent.

A new catalytic approach toward the symmetrical and nonsymmetrical etherification of benzyl alcohols was developed. The symmetrical etherification reaction was carried out in the presence of FeCl3·6H2O (5 mol %) as the catalyst and propylene carbonate as a green and recyclable solvent and led to the corresponding symmetrical ethers in 53 to 91% yields. The nonsymmetrical etherification of benzylic alcohols was achieved by using FeCl2·4H2O (10 mol %) in the presence of a pyridine bis-thiazoline ligand (12 mol %) and allowed for high selectivity and in 52 to 89% yields. These methods take advantage of eco-friendly conditions.

Chemically Modified Starches as Food Additives.

Starch is a renewable and multifunctional polysaccharide biopolymer that is widely used both in the food industry and other areas of the economy. However, due to a number of undesirable properties in technological processes, it is subjected to various modifications. They improve its functional properties and enable the starch to be widely used in various industries. A modified starch is a natural starch that has been treated in a way that changes one or more of its initial physical and/or chemical properties. Chemical modification consists of the introduction of functional groups into starch molecules, which result in specific changes in the physicochemical and functional properties of starch preparations. The bases of chemical modifications of starch are oxidation, esterification or etherification reactions. In terms of functionality, modified preparations include cross-linked and stabilized starches. These starches have the status of allowed food additives, and their use is strictly regulated by relevant laws. Large-scale scientific research is aimed at developing new methods of starch modification, and the use of innovative technological solutions allows for an increasingly wider use of such preparations. This paper characterizes chemically modified starches used as food additives, including the requirements for such preparations and the directions of their practical application. Health-promoting aspects of the use of chemically modified starches concerning resistant starch type RS4, encapsulation of bioactive ingredients, starch fat substitutes, and carriers of microelements are also described. The topic of new trends in the use of chemically modified starches, including the production of biodegradable films, edible coatings, and nanomaterials, is also addressed.

Mechanistic Avenues in the Chan-Lam-Based Etherification Reaction: A Computational Exploration.

Ongoing advances in CuII -catalyzed aerobic oxidative coupling reactions between arylboronic esters and diverse heteroatom nucleophiles have strengthened the development of the general Chan-Lam (CL)-based reaction protocol, including C-O bond formation methodologies. In-depth mechanistic understanding of CL etherification with specific emphasis on different reaction routes and their energetics are still lacking, even though the reaction has been experimentally explored. Here, we present a DFT-guided computational study to unravel the mechanistic pathways of CL-based etherification. The computational findings provide some interesting insights into the fundamental steps of the catalytic cycle, particularly the rate-determining transmetalation event. An aryl boronic ester-coordinated, methoxide-bridged CuII intermediate that acts as resting state undergoes transmetalation with an activation barrier of 20.4 kcal mol-1 . The energy spans of the remaining fundamental steps leading to the methoxylated product are relatively low. The minor p-cresol product requires an additional 14.2 kcal mol-1 energy span to surmount in comparison to the favored route. Hammett studies for the substituted aryl boronic esters reveal higher reaction turnovers for electron-rich aryl systems. The results agree with previously reported spectroscopic and kinetic observations. For a series of alcohol substrates, it was observed that, except for cyclohexanol, moderate to high etherification turnovers are predicted.

Effects of hydrogen peroxide on the low-temperature ignition delay times of ethylene/air/Ar mixtures in an RCM

Hydrogen peroxide with strong oxidative activity has received increasing attention in the field of ignition and combustion enhancement. To further seek out its potential benefits in ignition, the effects of hydrogen peroxide on the ignition delay times of ethylene were experimentally investigated using a rapid compression machine and numerically analyzed via the AramcoMech 3.0. The experiments with different levels of hydrogen peroxide (0 – 7000 ppm) were performed at Pc = 3.33 MPa, Tc = 817.9 – 921.0 K, φ = 0.5 – 1.5, and a dilution of 45 mol% Ar. Experimental results showed that adding hydrogen peroxide can effectively shorten the ignition delay times, and extend the low-temperature limitations. The improving effect was proceeded by three stages (0 – 1000 ppm, 1000 – 4000 ppm, and 4000 – 7000 ppm) of different decreasing rates. Kinetic analyses revealed that adding hydrogen peroxide promoted the production of OH radical to highlight the H-abstraction reaction of ethylene, further accelerating the oxidation of vinyl to vinyloxy and then to formaldehyde. Moreover, higher heat release rates were obtained with the addition of hydrogen peroxide for its exothermic character. By the kinetic effects of hydrogen peroxide addition, the ignition delay times of ethylene/air/Ar mixtures were significantly decreased. However, with the increase of additive fraction, the growth rate of both heat release rate and rate of production of OH radical were slowed down, lessening the enhancement effect on the ignition delay times.

Experimental and Simulation Studies for Purification and Etherification of Glycerol from the Biodiesel Industry

In this study, a purification route was applied to crude glycerol and its valorization via etherification was evaluated. Crude glycerol samples were obtained through transesterification reactions of soybean oil with methanol using potassium hydroxide as catalyst. A set of separation steps (acidification, neutralization, salt precipitation, evaporation and removal of contaminants using ion-exchange resins) was performed for purification of crude glycerol. The glycerol contents of crude samples were 46% wt., and for purified samples they were above 98% wt. The etherification reactions were carried out with purified samples and different alcohols (ethanol, isopropanol and 3-methyl-1-butanol) placed into a batch reactor, using a small amount of Amberlyst 15 as a catalyst, with autogenous pressure and solvent-free conditions. The glycerol conversion, selectivity and yield to ethers were evaluated. A glycerol conversion of up to 97% wt. was obtained when using ethanol. For isopropanol, the glycerol conversion rate was 85% (97.1% of monoether and 2.8% of diether). However, the selectivity to ethers for 3-methyl-1-butanol was negligible (<3% wt.). A process simulation for the purification and etherification steps integrated with a biodiesel production process was assessed in terms of productivity and energy consumption, considering different scenarios of glycerol/alcohol molar ratios. Finally, main impacts on the overall energy consumption were evaluated for the purification processes (glycerol and ethers).

Synthesis of Methyl Cellulose from Rice Husk Cellulose (Oryza sativa L.) with Methylene Chloride Through Etherification Reaction

Methyl cellulose is synthesized by an etherification reaction between α-cellulose created by isolating rice husks (Oryza sativa L.) with methylene chloride. Methylcellulose synthesis is performed by combining 1 g α-cellulose with acetone solvents at variations of methylene chloride 6 g, 8 g, 10 g, 12 g, and 14 g for 6 hours, resulting in 0.47 g, 0.60 g, 0.58 g; 0.51 g; and 0.69 g of methylcellulose. The results of methyl cellulose synthesis were tested with Degrees of Substitution, FT-IR spectroscopic analysis, and surface morphology using SEM. In the variation of methylene chloride, methylcellulose has the highest degree of replacement (14 g of 01,17). The formation of methyl cellulose is supported by FT-IR spectroscopy, namely with the appearance of vibration peaks in the wave number area of 3295.0 cm-1, which shows the -OH group, the C-H stretching group at wave number 2892.4 cm-1, the absorption peak that indicates the presence of C-O-C is found in wave numbers 1152.6 cm-1 and 1021.3 cm-1 where it is an asymmetrical and symmetrical stretching vibration. Morphological analysis using SEM showed that cellulose fibers' surface is smoother than methylcellulose. The average size of cellulose and methyl cellulose fibers is 4.791 μm and 3.828 μm, respectively. Morphological analysis using SEM showed that the surface fibers in cellulose were smoother than methylcellulose. The average size of cellulose and methyl cellulose fibers was 4.791 μm and 3.828 μm.

Synthesis, characterization, and properties of a novel propargyl ether naphthalene phenolic resin

AbstractIn this study, 1,5‐dihydroxynaphthalene moiety was introduced into a novolac resin structure, and propargyl ether naphthalene phenolic resin (PNPF) was synthesized by the Williamson etherification reaction, which improved the heat resistance of the resin and its processability. The structure of the PNPF resin was characterized using 1H NMR and FTIR analysis, and its processability, heat resistance, thermal expansion, and dielectric properties were evaluated. The results revealed that the addition of 1,5‐dihydroxylhine, increased the reaction activity of the PNPF resin, and decreased its initial curing temperature, with the resin exhibiting excellent processability. The cured resin also showed excellent heat resistance and thermomechanical properties. The 5% weight loss temperature (Td5) and glass transition temperature (Tg) of the resin increased to 437.61 and 362.04°C, respectively, while the coefficient of thermal expansion decreased from 60.17 to 44.52 ppm, with a reduction of 26.01%. Moreover, the dielectric constant and dielectric loss of the cured resin were 3.02 and 0.00239, respectively.

Synthesis of Cardanil Methyl Ether via Etherification Reaction Cardanol Isolated from Cashew Nut Shells (Anacardium occidentale L.) with Variations of Molar Methyl Iodide

The synthesis of the Cardanyl methyl ether is carried out through an etherization reaction between Cardanyl seed skin extract (CNSL) isolated from the methyl iodide. Cardanol is isolated with the addition of acetone, Ca(OH)2, NH4OH 25%, n-hexane: ethyl acetate (98:2), washing with NaOH 2.5%, HCl 5%, aquadest, and Na2SO4 anhydrate. The yield of the obtained cardanol is 74.39 g (74.39% of the initial weight of the CNSL) and has the following characteristics: acid count 1.2863 mgKOH/g, iodine count 215.6535 g I2/100 g, viscosity 38.7 cP, density 0.8266 g/mL, pH = 6.14. The FT-IR methyl ether Cardanyl spectrum shows an absorption band at 1162.9-1259.8 cm-1 shows a C-O stretching group at a wave number of 1043.6-1148.0 cm-1 showing the formation of an asymmetric and symmetrical C- O-C stretching band of the ether compound, the Spectra of the FT - IR methyl ether Cardanyl shows an absorptive band at 1162-1259-125,8 cm-1, showing a C-O stretching Group, at the wave number of 1043.6-1148.0 cm-1 indicating the formation, as a result, of an Asymmetric and Symmetric Stretching Group of the ethereal Compound. The Cardanyl methyl ether was synthesized by adding K2CO3, the solvent acetone and the iodide-methyl, with a reflux time of 8 hours. As for the parameters carried out in this study, the molar variation of the Cardanyl is the Methyl Iodide (1:1.5, 1:3, and 1:4.5) and yields 3.555 g; 12.084 g; 11.472 g of Cardanyl ether. Methyl ether Cardanyl was obtained in analysis with FT-IR and GC-MS spectroscopic photometers. The results of the analysis of Cardanyl methyl ethers with GC -MS were 63.28%, and the results of analysis of the Cardanyl ether with a variation of the molar ratio Cardanyl: Methyl iodide (1:1.5; 1:3; 1:4.5) with GC-MS obtaining 3.05%, 30.29%, and 26.58%. These results show the maximum percentage of methyl ethers Cardanyl at the reaction conditions of the variation molar ratios Cardanyl iodides (1:3), K2CO3 17.3 g, 50 mL of acetone, and 8 hours of reflux time.

Acid-Catalyzed Etherification of Glycerol with Tert-Butanol: Reaction Monitoring through a Complete Identification of the Produced Alkyl Ethers

Higher tert-Butyl glycerol ethers (tBGEs) are interesting glycerol derivatives that can be produced from tert-butyl alcohol (TBA) and glycerol using an acid catalyst. Glycerol tert-butylation is a complex reaction that leads to the formation of five tBGEs (two monoethers, two diethers, and one triether). In order to gain insight into the reaction progress, the present work reports on the monitoring of glycerol etherification with TBA and p-toluensulfonic acid (PTSA) as homogeneous catalysts. Two analytical techniques were used: gas chromatography (GC), which constitutes the benchmark method, and 1H nuclear magnetic resonance (1H NMR), whose use for this purpose has not been reported to date. A method for the quantitative analysis of tBGEs and glycerol based on 1H NMR is presented that greatly reduced the analysis time and relative error compared with GC-based methods. The combined use of both techniques allowed for a complete quantitative and qualitative description of the glycerol tert-butylation progress. The set of experimental results collected showed the influence of the catalyst concentration and TBA/glycerol ratio on the etherification reaction and evidenced the intrinsic difficulties of this process to achieve high selectivities and yields to the triether.

Mechanistic study of the production of ethylene glycol diacetate as a byproduct of the ethylene vapor phase process for vinyl acetate on PdAu(100) surface

With the rapid development of the photovoltaic industry, the demand for new materials such as EVA resin is increasing, and the study of its synthetic monomer vinyl acetate is of great significance. The ethylene vapor phase process is the current mainstream method for producing ethylene acetate. This method mainly uses a PdAu bimetallic catalyst to catalyze the production of ethylene acetate and water from ethylene, acetic acid and oxygen. The reaction process produces ethylene glycol diacetate, a high boiling point byproduct, which not only increases the energy consumption for separating the byproduct and reduces the selectivity of the target product but also may lead to catalyst deactivation. Therefore, reducing its production is of great importance in industrial production. The production mechanism of ethylene glycol diacetate is not clear due to the large variety of surface species and the complexity of the reaction in the ethylene vapor phase method, which makes it challenging to investigate the production mechanism of ethylene glycol diacetate directly by experimental means without interference. Molecular simulation techniques, especially Density Functional Theory (DFT) simulations and kinetic Monte Carlo (kMC) simulations, allow for a targeted study of the catalyst surface reaction mechanism to obtain the mechanism of ethylene glycol diacetate production.In this paper, the elementary reaction in the possible formation path of ethylene glycol diacetate on PdAu(100) surface has been studied by the DFT simulations, and the energy barrier and reaction heat of each elementary reaction have been obtained. Moreover, based on the DFT simulation data, the generation process of ethylene glycol diacetate on PdAu(100) surface is investigated by the kMC simulation, including the processes of reactant adsorption, intermediate species diffusion, surface reaction, and product desorption. The calculation results show that the species are mainly adsorbed on the Pd-Au bridge site or Pd top site; ethylene can firstly generate CH3COOCH2CH2, CH3COOCHCH2 or CH3COOCHCH species and then be combined with CH3COO species to produce ethylene glycol diacetate, where the energy barrier of the reaction of CH3COOCH2CH2 species with CH3COO species is lower than other two species with CH3COO species. The advantage generation path for the ethylene glycol diacetate on PdAu(100) surface is CH2CH2→CH3COOCH2CH2→CH3COOCH2CH2OCOCH3, and the rate-determining step is the reaction of ethylene with CH3COO species to form CH3COOCH2CH2 species.

Ferrierite nanosheets with preferential Al locations as catalysts for carbonylation of dimethyl ether

Enriching Al atoms in T2 and T4 sites of FER zeolite is decisive for achieving high catalytic activity in the carbonylation reaction of dimethyl ether (DME). Regulating the spatial position of Al atoms in targeted framework sites remains to be a great challenge during the synthesis of FER zeolite. The FER nanosheets with preferential Al-sitting in T2 and T4 sites were successfully synthesized with the assistance of cetyltrimethylammonium bromide (CTAB). The effect of CTAB on the morphology and Al distribution has been investigated in detail. CTAB mostly adsorbed on external surface serving as growth inhibitors, which resulted in nanosheet morphology and changed the length ratio along the b-axis to c-axis of the crystals. A minor portion of CTAB located in the channels may favor the spatial Al location in T2 and T4 sites, indicated by the results from 27Al MAS NMR spectra. The FER nanosheets exhibited improved DME conversion, stability, space–time yield (STY), and lifetime compared to conventional FER in DME carbonylation reaction.

A Combination of Computational and Experimental Studies to Correlate Electronic Structure and Reactivity of Donor–Acceptor Singlet Carbenes

AbstractMost of the reactivities of donor–acceptor (D–A) singlet carbenes are similar to metal carbenoids. However, the lone pair at the carbenoid carbon, coordinated with metal, is free in D–A carbene thereby making it nucleophilic as well. Herein, DFT-optimized structural features of D–A carbene has been investigated and is compared with rhodium carbenoid. It was observed that, when a D–A carbene reacts with cyclic-1,3-diones in different ethereal solvents, it is the lone pair at the sp2 orbital of the carbene that abstracts the proton from the enol form (of the cyclic-1,3-diones) to form a benzylic carbocation and an enolate. Subsequently, the carbocation undergoes nucleophilic attack by O of the ether solvents and then by the enolate to afford the desired ether-linked products. Accordingly, herein the reaction in THF, which otherwise had failed to work as a substrate in reported amino etherification reactions, worked well. DFT-calculated orbital energy levels and reaction profile support this reverse reactivity of singlet carbenes. Furthermore, HOMO–LUMO calculations indicated that electron-rich arenes in D–A carbene stabilizes the LUMO and destabilizes the HOMO which increases yield. Additionally, a library of 37 enol ether and 39 ether-linked compounds of potential medicinal relevance have been synthesized with good to excellent yields using numerous cyclic-1,3-diones.

Adsorption and surface reactions of C2H2 and C2H4 on Co(0001)

In this paper we have studied adsorption and surface reactions of acetylene and ethylene on Co(0001) in detail by temperature desorption spectrum (TDS), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). C2H4 adsorption at 130 and 300 K followed by subsequent heating mainly forms C2 clusters and graphitic carbon, respectively, while C2H4 decomposes at 400 and 500 K to form dominant graphitic carbon and carbon adatoms, respectively. C2H2 molecularly adsorbs at 130 K but exclusively dehydrogenates upon heating. The resulting C2H2(a) species at low coverages remains stable up to 400 K and then exclusively dehydrogenates into C2 clusters, while the resulting C2H2(a) species at high coverages remains stable up to 310 K and then majorly dehydrocyclizates into (C2H)n intermediates with ring structures at 340 K which further dehydrogenates into graphitic carbon, and minorly dehydrogenates into C2 clusters. Exposed at 370 K, C2H2 dehydrocyclizates into (C2H)n intermediates with ring structures. These temperature and coverage dependent surface reactions of C2H2 and C2H4 on Co(0001) greatly enrich our fundamental understanding of Co-catalyzed F-T synthesis reaction.

DESIDROGENAÇÃO CATALÍTICA OXIDATIVA DO ETANO UTILIZANDO CO2: UMA MINI REVISÃO

As a consequence of the greenhouse effect, there is a growing concern worldwide to reduce the amount of atmospheric carbon dioxide and a continuous effort by the scientific community to expand its use in various applications. Recently, CO2 has been used as an alternative, being applied as a light oxidant in the ethane oxidative dehydrogenation reaction, enabling new routes to obtain ethylene that are more efficient and economical than the current ones. Thus, the oxidative dehydrogenation of ethane with carbon dioxide stands out as one of the most promising alternatives, as it is an economical and ecological process, consuming one of the greenhouse gases. To analyze the literature on the relevance of the catalytic oxidative dehydrogenation reaction of ethane as an alternative route to ethylene production. This is a bibliographic review that used as source the databases of ELSEVIER, SPRINGER and CAPES from the descriptors "ODHE", "Oxidative catalytic dehydrogenation with CO2" and "ethene". Using the inclusion criteria, 50 articles in English and Portuguese published from 2012 to 2023 and a technical book were analyzed. CO2 is a promising alternative for the oxidative dehydrogenation reaction of ethane with O2, which suffers from catalyst deactivation due to coke formation and reducing selectivity to the main product. From the use of CO2 as an oxidant in the reaction, we have the advantage of producing active oxygen species, reducing coking and increasing selectivity. However, the great challenge is the development of catalysts that are active and selective to ethylene, with nickel oxide and cerium oxide emerging as promising alternatives, with high catalytic activity and favoring the redox cycle.

Selective Oxidative Dehydrogenation of Ethane and Propane over Copper‐Containing Mordenite: Insights into Reaction Mechanism and Product Protection

AbstractCopper(II)‐containing mordenite (CuMOR) is capable of activation of C−H bonds in C1‐C3 alkanes, albeit there are remarkable differences between the functionalization of ethane and propane compared to methane. The reaction of ethane and propane with CuMOR results in the formation of ethylene and propylene, while the reaction of methane predominantly yields methanol and dimethyl ether. By combining in situ FTIR and MAS NMR spectroscopies as well as time‐resolved Cu K‐edge X‐ray absorption spectroscopy, the reaction mechanism was derived, which differs significantly for each alkane. The formation of ethylene and propylene proceeds via oxidative dehydrogenation of the corresponding alkanes with selectivity above 95 % for ethane and above 85 % for propane. The formation of stable π‐complexes of olefins with CuI sites, formed upon reduction of CuII‐oxo species, protects olefins from further oxidation and/or oligomerization. This is different from methane, the activation of which proceeds via oxidative hydroxylation leading to the formation of surface methoxy species bonded to the zeolite framework. Our findings constitute one of the major steps in the direct conversion of alkanes to important commodities and open a novel research direction aiming at the selective synthesis of olefins.

Selective Oxidative Dehydrogenation of Ethane and Propane over Copper-Containing Mordenite: Insights into Reaction Mechanism and Product Protection.

Copper(II)-containing mordenite (CuMOR) is capable of activation of C-H bonds in C1 -C3 alkanes, albeit there are remarkable differences between the functionalization of ethane and propane compared to methane. The reaction of ethane and propane with CuMOR results in the formation of ethylene and propylene, while the reaction of methane predominantly yields methanol and dimethyl ether. By combining in situ FTIR and MAS NMR spectroscopies as well as time-resolved Cu K-edge X-ray absorption spectroscopy, the reaction mechanism was derived, which differs significantly for each alkane. The formation of ethylene and propylene proceeds via oxidative dehydrogenation of the corresponding alkanes with selectivity above 95 % for ethane and above 85 % for propane. The formation of stable π-complexes of olefins with CuI sites, formed upon reduction of CuII -oxo species, protects olefins from further oxidation and/or oligomerization. This is different from methane, the activation of which proceeds via oxidative hydroxylation leading to the formation of surface methoxy species bonded to the zeolite framework. Our findings constitute one of the major steps in the direct conversion of alkanes to important commodities and open a novel research direction aiming at the selective synthesis of olefins.

Additive-free synthesis of S-substituted isothioureas via visible-light-induced four-component reaction of α-diazoesters, aryl isothiocyanates, amines and cyclic ethers

An additive-free and environmentally friendly strategy has been realized for the construction of S-substituted isothioureas through visible-light-induced multicomponent reaction starting from α-diazoesters, aryl isothiocyanates, amines and cyclic ethers. This methodology features simple operation, mild reaction conditions, favorable functional group tolerance, easily available starting materials and high efficiency.

Hetero-Diels-Alder Cycloaddition Reaction of Vinyl Ethers Enables Selective Fluorescent Labeling of Plasmalogens in Human Plasma Lipids.

Plasmalogens (Pls) are vinyl ether-containing glycerophospholipids of broad biological interest. Their abnormal levels are associated with neurological disorders and cardiovascular diseases. The intricacy of analyzing Pls in lipid samples arises from the wide variety of other coexisting lipid species, which underscores the urgent need for a Pls-specific labeling reaction. To address this challenge, we report an efficient hetero-Diels-Alder cycloaddition reaction between nonterminal vinyl ethers of Pls and o-quinolinone quinone methide probes under mild conditions. On the basis of this mechanism, a selective fluorescent labeling method for Pls is developed. The application of this method permits the exclusive derivatization of Pls over other human plasma lipids. The process also imparts labeled Pls with distinct fluorescence emission and chromatographic retention properties. By integrating this method with high-performance liquid chromatography, we are able to identify individual chromatographic signatures of Pls from 10 different human plasma samples. This Pls signature analytical technique, empowered by the Pls-specific labeling reaction, is cost-effective and simple in terms of instrumentation, suggesting its promising potential for the early screening and diagnosis of diseases linked to Pls abnormalities.