Reaction Of Ethers Research Articles

Etherification of isoamyl alcohol using Amberlyst®15 as an acid catalyst

The present work reports on the production of di-isoamyl ether from the etherification of isoamyl alcohol, using the sulphonic resin Amberlyst®-15 (A-15) as a catalyst. Parameters such as temperature, reaction time and amount of catalyst were studied. Although the etherification reaction shows low conversions (9-18%), when glycerol is added to the reaction medium and an external pressure to the reaction system (3.5 atm), the conversion increases up to 40% and a yield up to 100% can be obtained towards di-isoamyl ether.

Pd-Catalyzed Site-Selective Defluorinative Etherification between Unactivated Perfluoroarenes and Hydrobenzoxazoles.

Polyfluoroaryl ethers represent an important framework of biologically active molecules and materials. Owing to the strong bond dissociation energy of C-F bond, selectivity and other issues, transition metal-catalyzed synthesis of polyfluoroaryl ethers from perfluoroarenes via the activation of C-F bond is challenging and underdeveloped, as compared to the well-documented C-O bond formation starting from aryl iodides, aryl bromides or aryl chlorides. Herein, an unprecedented Pd-catalyzed defluorinative etherification for the synthesis of polyfluoroaryl ether skeletons using hydrobenzoxazoles as phenol surrogate, has been reported. The substrate scope for this protocol is broad, with respect to hydrobenzoxazoles and perfluoroarenes, under mild reaction conditions. More importantly, challenging alkenyl and alkynyl substituted polyfluoroarenes could be successfully used as the coupling component for Pd-catalyzed etherification reaction. Density functional theory (DFT) calculations were employed to investigate the reaction mechanism, which suggested that oxidative addition between polyfluorobenzene and Pd(0) constituted the ratedetermining step.

Pickering emulsions stabilized by cellulose nanofibers with tunable surface properties for thermal energy storage

Cellulose nanofibers (CNFs) have been widely used as a renewable emulsifier to stabilize two immiscible liquids due to their intrinsic amphiphilicity and excellent emulsifying ability. However, it remains challenging to fully understand the effects of carboxylate group content and surface charge density on the emulsifying ability of CNFs and the stability of Pickering emulsion. Herein, carboxymethylated CNFs were extracted from bleached kraft pulp using etherification reaction and high-pressure homogenization, allowing for easy surface charge density and size adjustment by changing sodium chloroacetate content and homogenization cycles. The optimizing CNFs possessed a high Zeta potential (−71.2 mV) and a suitable carboxylate group content (1.81 mmol/g), which enabled CNFs to irreversibly adsorb at the hydrophobic paraffin wax (PW) droplet surface and form interfacial steric barriers, providing large electrostatic repulsion between the PW droplets against coalescence. Thus, the CNF-stabilized PW emulsions could be stored for more than 6 months. Moreover, the phase change enthalpy of the freeze-dried emulsion is as high as 193.7 J/g, which provides the emulsion to reversibly store and release heat. This work provides a comprehensive insight into the interfacial stability mechanism of CNFs as stabilizers and facilitates the potential application in thermal energy storage.

Chemical thermodynamics of biomass, cellulose, and cellulose derivatives: A review

This article provides a review of the research on the chemical thermodynamics and thermochemistry of biomass, cellulose, and its derivatives such as ethers, esters, and oxycelluloses. For diverse biomass types, gross and net heating values were studied. It has been established that these energetical characteristics of biomass can be calculated using a superposition of the energetical characteristics of the main components of biomass such as cellulose, hemicelluloses, lignin, lipids, proteins, etc. The pelletization of biomass improves its fuel performance. It was shown that, if the ultimate goal is to generate the maximum amount of thermal energy, then it is more profitable to directly burn the initial biomass in the form of pellets than to burn the amount of solid or liquid biofuel that can be extracted from this biomass. After the cellulose study, the direct and exact thermochemical method for determining the crystallinity degree of this biopolymer was proposed. In addition, the standard combustion and formation enthalpies of various cellulose samples were studied. As a result, the thermodynamic characteristics of four crystalline allomorphs of cellulose, CI, CII, CIII, and CIV, were obtained and their thermodynamic stability was evaluated. The thermochemistry of enzymatic hydrolysis of cellulose was studied. In addition. The thermodynamical characteristics of various cellulose derivatives were determined, and the thermochemistry of the reactions of cellulose alkalization, etherification, esterification, and oxidation was studied.

Visible-Light-Induced Three-Component Reactions of α-Diazoesters, Indazoles and Cyclic Ethers

An efficient method was developed for construction of N-short-chain ether attached carbonyl group-substituted indazoles. The visible-light-induced three-component reactions of α-diazoesters, indazoles and cyclic ethers, under extremely mild conditions, led to the corresponding mixture of N1 and N2 short-chain ether substituted indazoles in good to excellent yields.

Arylthianthrenium Salts for Triplet Energy Transfer Catalysis.

Sigma bond cleavage through electronically excited states allows synthetically useful transformations with two radical species. Direct excitation of simple aryl halides to form both aryl and halogen radicals necessitates UV-C light, so undesired side reactions are often observed and specific equipment is required. Moreover, only aryl halides with extended π systems and comparatively low triplet energy are applicable to synthetically useful energy transfer catalysis. Here we show the conceptual advantages of arylthianthrenium salts (ArTTs) for energy transfer catalysis with high energy efficiency compared to conventional aryl (pseudo)halides and their utility in arylation reactions of ethylene. The fundamental advance is enabled by the low triplet energy of ArTTs that may originate in large part from the electronic interplay between the distinct sulfur atoms in the tricyclic thianthrene scaffold, which is not accessible in either simple (pseudo)halides or other conventional sulfonium salts.

An Aza‐Prilezhaev‐Based Method for Inversion of Regioselectivity in Stereospecific Alkene 1,2‐Aminohydroxylations

AbstractUnder acidic conditions (TFA) and in the presence of water, BocNHOTs promotes stereospecific 1,2‐aminohydroxylations of alkenes. The processes involve intermolecular aza‐Prilezhaev aziridination followed by stereospecific SN2 opening by water. This reagent combination provides regiochemical outcomes that are opposite to, or more selective than those observed using epoxidation initiated 1,2‐aminohydroxylation protocols. Replacement of water by other nucleophiles allows 1,2‐amino(thio)etherification, diamination, aminoazidation and aminofluorination reactions. Intramolecular processes are also feasible, including unusual variants that evoke azabicyclobutane‐like reactivity.

An Aza-Prilezhaev-Based Method for Inversion of Regioselectivity in Stereospecific Alkene 1,2-Aminohydroxylations.

Under acidic conditions (TFA) and in the presence of water, BocNHOTs promotes stereospecific 1,2-aminohydroxylations of alkenes. The processes involve intermolecular aza-Prilezhaev aziridination followed by stereospecific SN2 opening by water. This reagent combination provides regiochemical outcomes that are opposite to, or more selective than those observed using epoxidation initiated 1,2-aminohydroxylation protocols. Replacement of water by other nucleophiles allows 1,2-amino(thio)etherification, diamination, aminoazidation and aminofluorination reactions. Intramolecular processes are also feasible, including unusual variants that evoke azabicyclobutane-like reactivity.

Bio-Based Self-Healing Epoxy Vitrimers with Dynamic Imine and Disulfide Bonds Derived from Vanillin, Cystamine, and Dimer Diamine.

The condensation reactions of 4,4'-(ethane-1,2-diylbis (oxy)) bis(3-methoxybenzaldehyde) (VV) with cystamine, 1,6-hexamenthylene diamine, and a dimer diamine (PriamineTM 1075) produced three types of vanillin-derived imine-and disulfide-containing diamines (VC, VH, and VD, respectively). Thermal curing reactions of polyglycerol polyglycidyl ether with VD and mixtures of VC/VD and VH/VD produced bio-based epoxy vitrimers (BEV-VD, BEV-VC/VD, and BEV-VH/VD, respectively). The degree of swelling and gel fraction tests revealed the formation of a network structure, and the crosslinking density increased with a decreasing VD fraction. The glass transition temperature, tensile strength, and tensile modulus of the cured films increased as the VD fraction decreased. In contrast, the thermal degradation temperature of the cured films increased as the VD fraction increased. All the cured films were healed by hot pressing at 120 °C for 2 h under 1 MPa at least three times. The healing efficiencies, based on tensile strength after the first healing treatment, were 75-78%, which gradually decreased as the healing cycle was repeated. When imine-and disulfide-containing BEV-VC/VD and imine-containing BEV-VH/VD with the same VC/VD and VH/VD ratios were used, the former exhibited a slightly higher healing efficiency.

Surprising Dynamics Phenomena in the Diels-Alder Reaction of C60 Uncovered with AI.

We performed an extensive artificial intelligence-accelerated quasi-classical molecular dynamics investigation of the time-resolved mechanism of the Diels-Alder reaction of fullerene C60 with 2,3-dimethyl-1,3-butadiene. In a substantial fraction (10%) of reactive trajectories, the larger C60 noncovalently attracts the 2,3-dimethyl-1,3-butadiene long before the barrier so that the diene undergoes the series of complex motions including roaming, somersaults, twisting, and twisting somersaults around the fullerene until it aligns itself to pass over the barrier. These complicated processes could be easily missed in typically performed quantum chemical simulations with shorter and fewer trajectories. After the barrier is passed, the bonds take longer to form compared to the simplest prototypical Diels-Alder reaction of ethene with 1,3-butadiene despite high similarities in transition states and barrier widths evaluated with intrinsic reaction coordinate (IRC) calculations. C60 is mainly responsible for these differences as its reaction with 1,3-butadiene is similar to the reaction with 2,3-dimethyl-1,3-butadiene: the only substantial difference being that the extra methyl groups double the probability of the prolonged alignment phase in dynamics. These additional calculations of C60 with 1,3-butadiene could be performed via active learning more easily by reusing the data generated for the other two reactions, showing the potential for larger-scale exploration of the effects of different substrates in the same types of reactions.

Benzoic Acid Serves as Precursor of Catalytic HAT Reagent in a Two-Molecule Photoredox System.

The photoinduced regioselective HAT reactions of acetals, ethers, and alcohols using benzoic acids in a two-molecule photoredox system led to the formation of new C-C bonds with alkenes under mild conditions. Aryl carboxy radicals generated from benzoic acids in a two-molecule photoredox system can function as catalytic HAT reagents, even though an excess amount of a hydrogen donor substrate is required. Various acetals, ethers, alcohols, and alkenes can be employed in the photoreaction to provide both high yields of adducts and high recoveries of benzoic acids.

Optimization of synthesis of cationic starches for wastewater sludge and microalgae separation

The implementation of stricter water protection legislation requires the development of novel environmentally friendly water treatment materials. A new method for the preparation of water soluble cationic starch flocculants using potato starch, 3-chloro-2-hydroxypropyltrimethylammonium chloride and CaO additive was developed and surface response methodology was successfully utilized for the optimization of degree of substitution in the cationization of potato starch with and without CaO additive. Based on the results of destabilization studies of model kaolin, wastewater sludge, and microalgae dispersion systems, optimized conditions ware proposed for obtaining an efficient, soluble, and biodegradable cationic starch flocculant with optimal structure. The duration of starch etherification reaction was reduced to <12 h to obtain soluble cationic starch derivatives with a degree of substitution of quaternary ammonium groups of 0.25, which retained the granular structure during synthesis. An efficient flocculation technology using anionic polymer and high content of biodegradable cationic flocculant was proposed. The highly efficient flocculation of microalgae suspensions using developed cationic starch derivative with the degree of substitution of cationic groups of 0.25 has been also achieved. The developed environmentally friendly cationic starches with tailored flocculation properties proofed to have a great potential in various water cleaning and separation technologies with prospects in wastewater treatment, agriculture or energy sectors.

Catalytic Cycloaddition Reactions of Ynol and Thioynol Ethers

Comprehensive SummaryElectron‐rich alkynes, such as ynol and thioynol ethers, have proven to be versatile and appealing partners in catalytic cycloaddition reactions, and thus have raised considerable attentions owing to the practical application in the modular assembly of valuable carbo‐ and heterocycles. The past decades have witnessed inspiring advances in this emerging field, and an increasing number of related discoveries have been exploited. Divided into two main sections on the basis of substrate type, in each section this comprehensive review will initially summarize their synthetic preparations and subsequently examine their reactivity in every sort of catalytic cycloaddition with emphasis on the methodology development, aimed at providing an access to this burgeoning area and encouraging further innovations in the near future. Key ScientistsFor the cycloaddition of ynol ethers, in 2004, Kozmin et al. firstly developed a silver‐catalyzed [2 + 2] cycloaddition of siloxy alkynes with electron‐poor olefins. In 2012, Hiyama et al. realized a palladium‐catalyzed formal [4 + 2] annulation of alkynyl aryl ethers with internal alkynes. In the same year, Sun et al. discovered an efficient [6 + 2] cyclization between siloxy alkynes and 2‐(oxetan‐3‐yl)benzaldehydes by applying HNTf2 as catalyst. In 2017, Wender et al. first utilized vinylcyclopropanes (VCPs) as coupling partners in the [5 + 2] annulation of ynol ethers. In 2018 and 2020, Ye et al. reported zinc‐catalyzed formal [3 + 2] and [4 + 3] cycloaddition, respectively. For the cycloaddition of thioynol ethers, in 2004, Hilt et al. realized a [4 + 2] cycloaddition by employing the alkynyl sulfides and acyclic 1,3‐dienes. In 2006, a ruthenium‐catalyzed [2 + 2] cycloaddition of thioynol ethers with bicyclic alkenes was accomplished by Tam. In 2014, Sun et al. reported an elegant iridium‐catalyzed click reaction of thioalkynes with azides.

Visible-Light-Induced Multi-Component Nitrooxylation Reactions of α-Diazoesters, Cyclic Ethers, and Tert-Butyl Nitrite Leading to Organic Nitrate Esters.

A simple and efficient strategy has been developed for the synthesis of organic nitrate esters via visible-light-induced multi-component nitrooxylation reactions of α-diazoesters, cyclic ethers, and tert-butyl nitrite under open air atmosphere. This transformation could be conducted under mild and metal-free conditions to provide a number of organic nitrate esters in moderate to good yields using air as the green oxidant.

Switchable transformation of biomass-derived furfural to furfuryl alcohol and isopropyl furfuryl ether over a zirconium-based bifunctional catalyst

Selectively converting biomass-derived furfural (FF) to furfuryl alcohol (FFA) and isopropyl furfuryl ether (IPFE) via the same catalytic system is an important strategy for the production of high-value chemicals and fuels. However, this strategy still faces a great challenge because the formation of FFA and IPFE requires different catalyst types and reaction conditions. Hence, developing a compatible catalytic system is extremely necessary. In this work, we designed a high-efficiency zirconium-based bifunctional catalyst (Zr-HC-SO3H), simultaneously containing Lewis acid-base sites (Zr4+–O2−) and Brønsted acid sites (–SO3H), which were mainly responsible for the Meerwein-Ponndorf-Verley reduction reaction of FF and further etherification reaction of FFA, respectively. By controlling reaction conditions, the action orders and catalytic activities of Zr4+–O2− and –SO3H could be accurately regulated. Thus, Zr-HC-SO3H showed excellent catalytic performance for the switchable transformation of FF, leading to 98.9 % FFA yield at 120 °C for 4 h and 95.1 % IPFE yield at 170 °C for 12 h in isopropanol (iPrOH). Additionally, the analysis results of reaction pathways indicated that the etherification of FFA was much more difficult than the reduction of FF over Zr-HC-SO3H in iPrOH, so IPFE was only formed under the harsher reaction conditions. More significantly, Zr-HC-SO3H also catalyzed the switchable transformation of many other carbonyl compounds and demonstrated satisfactory catalytic universality in iPrOH. In conclusion, this work offered some momentous clues for the development of multipurpose catalytic systems and the controllable synthesis of valuable products in the biorefinery process.

Improving the Sustainability of Enzymatic Synthesis of Poly(butylene adipate)-Based Copolyesters: Polycondensation Reaction in Bulk vs Diphenyl Ether.

In response to mounting global concerns such as CO2 emissions, environmental pollution, and the depletion of fossil resources, the field of polymer science is shifting its focus toward sustainability. This research investigates the synthesis of poly(butylene adipate)-co-(dilinoleic adipate) (PBA-DLA) copolymers using two distinct methods: bulk polycondensation and polycondensation in diphenyl ether. The objective is to assess the environmental impact, chemical structure, composition, and key properties of the resulting copolymers, with a particular emphasis on determining the viability of bulk synthesis as a more sustainable approach. Various analytical methods, including nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and size exclusion chromatography, were employed to confirm successful copolymerization and highlight differences in molecular weight and microstructure. Additionally, thermal and dynamic mechanical analyses were conducted to thoroughly characterize the copolymers' properties. This research provides significant findings into the sustainable production of PBA-DLA copolymers, offering a more environmentally friendly approach without compromising product quality or performance.

Pd(0)/Xantphos-Catalyzed Benzylic C(sp3)-O Arylation of Benzyl Heteroaryl Ethers: Reduction of Pd(II) to Pd(0) by Xantphos.

Herein, we report the synthesis of 1,1-diarylmethanes via palladium-catalyzed benzylic C(sp3)-O arylation of benzyl alcohol derivatives. An efficient, straightforward approach to synthesizing Pd(0)(xantphos)2 was developed through in situ reduction of Pd(II) to Pd(0) with the bidentate tertiary phosphine xantphos, which proved to be a highly active precatalyst in the Suzuki-Miyaura cross-coupling reaction of benzyl heteroaryl ethers.

Lignin-based vitrimer containing dynamic borate ester bonds with intrinsic photoconversion and excellent photothermal remoldability

The development of photoresponsive shape memory materials based on the photothermal conversion properties of lignin and the low activation energy of the dynamic covalent borate bond is of great importance. In this paper, a kind of lignin-based vitrimer polymer (LBP) containing dynamic boronic ester bonds was prepared by a “sulfhydryl-epoxy” click reaction and etherification reaction. The results show that the rigid segment EP-EL (lignin-based epoxy resin) and BDB (2,2′-(1,4-phenylene)-bis-[4-mercapto-1,3,2-dioxaneborane]) with benzene ring structure can impart tensile strength (20.8 MPa) to the LBP, while the flexible segment PEG imparts good elongation at break (15 %). The dynamic binding and dissociation exchange mechanism of the boronic ester bonds enables LBP to exhibit thermal remodelling properties (up to 36.2 %) and water-assisted self-healing properties at room temperature (up to 49.0 %). In addition, LBP exhibits excellent thermal and light-responsive shape memory properties due to its own photothermal conversion performance (photothermal conversion efficiency up to 18.2 %) and the dynamic boronic ester bond thermal activation bond exchange mechanism. The insulating properties of LBP make it suitable for use in high temperature protection circuit devices and light-responsive circuit devices. This study provides new insights into the design and application of Vitrimer and photoresponsive shape memory polymers, and also offers a new avenue for high-value utilization of lignin.

Electrocatalytic Radical Cation Diels-Alder Reactions Using Enol Ethers As Dienophiles

Single-electron oxidation enables the conversion of electron-rich alkenes such as styrene derivatives to radical cation species. We have been developing various cycloaddition reactions of radical cations produced by single-electron oxidation using electrochemical and TiO2 photochemical methods. Introducing an electron-rich aryl group which we call a redox tag is a critical part of the process to control the reactivity of the radical cations. During carbon-carbon bonds formation the motif functions as both electron donor and electron acceptor. In addition to styrene derivatives, enol ethers can also be readily oxidized by single electron transfer (SET) electrochemically or photochemically to generate the radical cations. For instance, enol ethers tethered redox tag serves efficient radical cation precursors for [2+2] cycloadditions.[1] The cycloadditions are net redox-neutral reactions and are initiated by the formation of a radical cation by single-electron oxidation and completed by reduction after ring formation.Herein, we present [4+2] cycloadditions using enol ethers as dienophiles by electrochemical oxidation in lithium perchlorate (LiClO4)/nitromethane (MeNO2) system. In the case of disubstituted enol ethers prepared from aldehydes, the approach involving redox tag was successful in obtaining the corresponding cycloadducts, while the desired products were not obtained when the substrates without redox tag were subjected.[2] This result suggests that intramolecular electron transfer from the redox tag is crucial for the formation of the cyclohexene ring systems. In contrast, the trisubstituted enol ethers prepared from ketones allowed the cycloaddition reaction to proceed without the involvement of redox tag. It is expected that the methyl group significantly stabilizes the cyclohexene radical cations to have enough lifetime to be reduced by intermolecular SET. Furthermore, since the cycloaddition reaction of enol ether was completed with a catalytic amount of electricity (0.4 F/mol), a radical cation chain mechanism is proposed in which electron acts as a catalyst.

Synthesis of thioester-functionalized 2H-benzopyrans through palladium-catalyzed one-pot cyclization/thiocarbonylation using sulfonyl chlorides as the sulfur sources

A general and efficient protocol for the synthesis of thioesters-functionalized 2H-benzopyrans has been developed through a palladium-catalyzed one-pot cyclization/thiocarbonylation reaction of propargyl ethers with sulfonyl chlorides as promising and easily accessible sulfur sources. The reaction showed good compatibility towards versatile functional groups, both aryl and alkylsulfonyl chlorides were well tolerated. Without any external reductant, using Mo(CO)6 as a convenient CO source, a wide range of 2H-benzopyrans bearing thioester as an attractive functional group were obtained in moderate to good yields.