Symmetrical Ethers Research Articles

Titanium tetrafluoride catalysis for the dehydrative conversion of diphenylmethanols to symmetric and unsymmetric ethers.

In contrast to the conversion of diphenylmethanol to the corresponding halides with an equivalent of titanium tetrachloride or -bromide, catalytic (50 mol%) titanium tetrafluoride converts benzhydrols in diethyl ether or dichloromethane to bis(benzhydryl) ethers within 0.5-1 h at room temperature. Cross ether formation with diphenylmethanols and primary aryl or aliphatic alcohols is achieved in the presence of 25 mol% TiF4 in refluxing toluene as solvent. A tentative mechanism involving a carbocation intermediate has been proposed.

Ether, sulfide and sulfone derivatives of cinnamaldehyde: Insights into synthesis, structural elucidation and solvatochromism

Symmetric ether, sulfide and sulfone derivatives based on Schiff base functionalized group (3a-c) were synthesized via classical condensation of 4,4′-diaminodiphenyl precursors (1a-c) and cinnamaldehyde (2) in methanol at ambient reaction settings. The compounds were characterized using CHN, UV–Vis, FTIR, and 1H- and 13CNMR . The origin of absorption spectra was chased using Time-Dependent Density-Functional Theory (TD-DFT) in order to figure out the electronic transitions. The compounds exhibited almost a similar electronic potential as displayed by the molecular electrostatic potential. The energy gap of these materials was extracted from the computational approaches, showing ΔE of 3.778, 3.724, and 4.014 eV respectively for 3a, 3b, and 3c. These values were further harnessed to estimate the global reactivity parameters. Moreover, the electrophilic and nucleophilic points were examined through surface analysis of the optimized structures via DFT simulations. Such investigations support the compounds’ molecular structures via common noncovalent interaction, like hydrogen bonding and non-classical CH…π forces. Experimental and computational findings were in a respectable agreement to display that only compound 3c possesses the ability of altering its maximum absorption under different solvent conditions. A substantial shifting of the maximum absorption was noticed with ethyl alcohol at λmax = 321 nm, referring to a 32 nm of blue shift in respect to acetic acid, which could be responsible for the partial protonation of the sulfone group.

Conformation-aggregation interplay in the simplest aliphatic ethers probed under high pressure.

The structures of the simplest symmetric primary ethers [(CnH2n+1)2O, n = 1-3] determined under high pressure revealed their conformational preferences and intermolecular interactions. In three new polymorphs of diethyl ether (C2H5)2O, high pressure promotes intermolecular CH...O contacts and enforces a conversion from the trans-trans conformer present in the α, β and γ phases to the trans-gauche conformer, which is higher in energy by 6.4 kJ mol-1, in the δ phase. Two new polymorphs of dimethyl ether (CH3)2O display analogous transformations of the CH...O bonds. The crystal structure of di-n-propyl ether (C3H7)2O, determined for the first time, is remarkably stable over the whole pressure range investigated from 1.70 up to 5.30 GPa.

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.

Efficient synthesis, characterization and electrochemical properties of bis(ferrocenyl) ethers

Three different symmetrical ethers derived from formyl ferrocene, acetyl ferrocene and benzoyl ferrocene have been characterized via FT-IR, UV-Visible and 1H NMR spectroscopic techniques. Further, the true nature of bis[phenyl(ferrocenyl)methyl]ether was confirmed by single crystal X-ray diffraction analysis. The redox behavior of ferrocenyl ethers has been studied using cyclic voltammetry. The present method yields the corresponding bisferrocenyl ether with almost 100 % conversion.

Polyether Synthesis through Reductive Etherification Reaction Strategy

AbstractThe reductive etherification reaction (RER) of carbonyl groups (aldehydes or ketones) through silane as a reducing agent together with Bronsted or Lewis acid affords the synthesis of symmetrical and unsymmetrical ethers. This strategy is applied at the macromolecular level for the first time in 1993, and isophthalaldehyde is self‐polymerized in the presence of triethylsilane (Et3SiH)/ tritylperchlorate (TrClO4) to yield polyethers with low to moderate molecular weights. Next, the polyethers with alternating structures are achieved by reacting isophthalaldehyde with bis(trimethylsilyl) ethers or diols as comonomers using reducing agent silane and Lewis acid. Moreover, in recent years, it is shown that polyether synthesis and post‐polymerization modification (PPM) of polymers proceeds smoothly and effectively with the RER strategy in the presence of chlorodimethylsilane (CDMS), which acts as both a reducing agent and a Lewis acid.

Preparation and structure–property relationship of flexible aramid films with enhanced strength by introducing asymmetric and symmetric aromatic ether bond structures

The flexible molecular segments and aggregated structures of MAPB–PMIA and PAPB–PMIA endow polymers with soft properties with high extension and low modulus.

Chiral Crown Ethers Accessed from Catalytic Enantioselective Desymmetrization Reactions.

A diversity of unprecedented chiral aza-crown ethers were synthesized straightforwardly from readily available and inexpensive aza-crown ethers. Catalyzed by a chiral phosphoric acid, desymmetrization of an array of symmetric N-arylated aza-crown ethers through tert-amino reaction proceeded efficiently under mild conditions to produce novel tetrahydroquinoline-fused aza-crown ethers in good to excellent yields with up to 96% ee. Our strategy opens a new route to functionalized chiral crown ethers.

A detailed high-pressure oxidation study of di-isopropyl ether

The oxidation of di-isopropyl-ether (DIPE) was studied in a jet-stirred reactor. Fuel-lean, stoichiometric, and fuel-rich mixtures (φ = 0.5–4) were oxidized at a constant fuel mole fraction of 1000 ppm, at temperatures ranging from 500 to 1160 K, at 10 atm, and constant residence time of 0.7 s. The chosen conditions are consistent with our previous studies on ether oxidation. Mole fraction profiles were obtained through sonic probe sampling, and analyzed by gas chromatography and Fourier transform infrared spectrometry. As opposed to our previous studies on ethers (S. Thion et al. 2017, Z. Serinyel et al. 2018 and 2020), DIPE showed no low-temperature reactivity under the same experimental conditions. Oxidation of the rich mixture showed similarities to pyrolysis producing important quantities of propene and isopropanol, while no isopropanol is observed under lean conditions. In terms of overall reactivity, DIPE showed smaller fuel conversion compared to other symmetric ethers previously studied. The present data and literature experiments were simulated with our ether oxidation mechanism showing good agreement.

Bimetallic‐Catalyzed Oxidative Esterification Reaction Forming α‐Acyloxy Ether

AbstractA bimetallic‐catalyzed oxidative esterification reaction has been conducted between non‐activated C(sp3)–H bonds of symmetric ethers and carboxylic acids with the presence of di‐tert‐butyl peroxide as the oxidant through a cross‐dehydrogenative coupling (CDC) reaction. This approach allows the derivatives of cyclic ether substrates to interact with aromatic acids, giving excellent yields for the formation of α‐acyloxy ethers. The bimetallic organic frameworks catalyst (Fe2Ni‐BDC) that had been synthesized by solvothermal method was successfully utilized for the formation of α‐acyloxy ethers based on the CDC reaction of carboxylic acid with diethylene oxide (approx. 84 % product yield). Besides, this material was also used as catalyst for research scope of benzoic acid containing various substituents.

Adsorption and catalytic study of cyclopentyl methyl ether formation: structure-activity interplay in medium-pore zeolites

Symmetrical and asymmetrical ethers produced from renewable feedstock play a key role in numerous green chemistry technologies. The aim of our contribution is to understand how textural properties and the location of active sites affect the mechanism of cross-etherification of cyclopentanol with methanol, which yields the asymmetric product cyclopentyl methyl ether. For this purpose, commercial MFI, nanosponge MFI, and nanolayered MFI zeolites with similar concentrations of acid sites, as well as medium-pore TUN and IMF zeolites with internal voids, slightly larger than those of MFI, were investigated by combining catalytic tests with infrared adsorption studies. Detailed FTIR analysis revealed three adsorption adducts, whose fractions varied with the alcohol loading and with the type of zeolite: i) a neutral single H-bonded adduct, ii) a bulky ionic H-bonded adduct, and iii) a neutral cyclopentoxy group. MFI zeolite is the most efficient catalyst in cyclopentanol cross-etherification, reaching 70% cyclopentyl methyl ether yield. Both hierarchical (48%-42%) and medium-pore (48%-58%) zeolites exhibited significantly reduced cyclopentyl methyl ether yields due to their larger internal voids and high number of strong Lewis acid sites, which presumably catalyze the undesired reaction of cyclopentanol dehydration to cyclopentene.

The dehydrative etherification of benzyl alcohols via mechanochemical reaction

A facile, solvent-free, lower-cost, and efficient high-speed ball milling reaction catalyzed by Cu(NO3)2·3H2O/P2O5 is developed for the synthesis of symmetric ethers from dehydration of benzyl alcohols by taking a benzylic carbocation as intermediate.

Dimethyl ether oxidation analyzed in a given flow reactor: Experimental and modeling uncertainties

Dimethyl ether (DME), a widely studied alternative fuel, is known to exhibit complex low- and high-temperature oxidation chemistry. It is also the smallest molecule in the families of symmetric ethers and oxymethylene ethers that receive attention as renewable fuels. Thanks to several studies performed in facilities such as shock tubes, jet-stirred reactors and flames, it can be assumed that the DME oxidation is well understood. However, DME oxidation in flow reactors has been addressed comparatively rarely, although this configuration presents an interesting system with influences of both kinetics and fluid dynamics on the reaction behavior. To examine the interplay of both influences and potential uncertainties resulting from such effects, DME oxidation was experimentally investigated over an extended range of conditions in a flow reactor equipped with mass-spectrometric analysis. Quantitative species profiles were obtained at near-atmospheric pressure in a temperature range of 400–1100 K for three equivalence ratios φ (0.8, 1.0 and 1.2), and three flow rates at each stoichiometry. These nine different cases were first analyzed using a detailed chemical reaction mechanism with a Plug-Flow Reactor (PFR) model. In-depth examination of experimental and reaction model uncertainties led to updates in the reaction mechanism that were performed on the basis of most recent, reliable kinetic information. In spite of the good agreement of the PFR model with the experimental data at selected conditions, especially in the low-temperature regime, substantial deviations in the reactivity and associated species profiles were noted in several cases, particularly for lean conditions at low flow rates and intermediate temperatures around and above 700 K. A two-dimensional (2D) computational fluid dynamics (CFD) model was therefore employed to characterize the reactive flow conditions more accurately. Significant contributions of fluid dynamics effects were observed in the cases that presented the most severe deviations, and overall good agreement within experimental uncertainty was obtained for the nine cases with the 2D simulations. With the aid of a mathematical curve matching procedure using a variety of recent, established kinetic mechanisms, it could be convincingly demonstrated under the current conditions that improvements in predictive modeling capability in the sensitive test cases were not a question of improved kinetics but were mainly achieved by considering the two-dimensional reactive flow. As a consequence, the present investigation can serve to alert the community to the potential major influences that might be neglected if standard PFR models are used to predict fuel oxidation without detailed analysis whether the conditions are suited to that approach.

Synthesis of a Mechanically Planar Chiral and Axially Chiral [2]Rotaxane.

In this study, we synthesized a [2]rotaxane that was both mechanically planar chiral and axially chiral, comprising a symmetrical bis-crown ether featuring a biphenyl moiety (as the macrocyclic component) and a symmetrical bis-ammonium salt (as the dumbbell-shaped component).

Symmetric Ethers as Bioderived Fuels: Reactivity with OH Radicals

Research reported in this publication was funded by the Office of Sponsored Research at King Abdullah University of Science and Technology (KAUST)

Investigations of prenol reactions catalyzed by zinc and molybdenum complexes

We demonstrate the formation of symmetrical and unsymmetrical allylic ethers with molybdenum catalysts for the first time. While conducting reactivity studies of biobased oxygenates as fuel blending components in the presence of molybdenum or zinc metal complexes commonly used as lubricant additives, we discovered that prenol (3-methyl-2-buten-1-ol), a promising oxygenate with good fuel properties, undergoes unexpected chemical transformations. Interestingly, its isomer, isoprenol (3-methylbut-3-en-1-ol) was unreactive towards the same metal complexes. Moreover, the results suggest that the transformations were catalytic in nature as only 1% (w/w) of lubricant molybdenum complex (Molyvan L – molybdenum di (2-ethylhexyl) phosphorodithioate) led to the almost complete consumption of prenol under certain conditions. The zinc complex (zinc dialkyldithiophosphate) also led to a rich product profile, perhaps to a lower extent than the molybdenum analog. Intrigued by these results, we fine-tuned reaction conditions (e.g., temperature, solvents, closed reactor, or reflux set-up) to maximize the conversion of prenol and generation of byproducts, enable scale-up, and subsequently separate and identify the main components found in the mixture. We determined that the most efficient reaction was neat (prenol with 1% (w/w) molybdenum catalyst) under reflux conditions and at mild temperatures (<120 °C) with 95% conversion of prenol and formation of four major products. The product profile was identified spectroscopically (nuclear magnetic resonance spectroscopy, gas chromatography via flame ionization detection, and gas chromatography-mass spectroscopy) and included isoprene, 2-methylbut-3-en-2-ol (prenol isomer alcohol), 3-methyl-3-((3-methylbut-2-en-1-y)oxy)but-1-ene (mixed alcohol ether), and 1,1′-oxybis(3-methyl-2-butene) (prenol ether). The products are consistent with the catalytic isomerization of prenol to generate a tertiary unsaturated alcohol, as well as inter and intramolecular dehydration chemistries of the two alcohols that formed ethers and isoprene, respectively. This finding is significant as it demonstrates potentially undesirable chemistries that take place when lubricants and fuels come in contact, such as the sump pump or in-cylinder. Moreover, the fuel chemistry observed in real-life scenarios may be due in part to formed by-products and not the starting oxygenate. This work highlights potential catalytic chemistries that can occur with other metal complexes commonly found in lubricants. To the best of our knowledge, this is the first demonstration of the formation of symmetrical and unsymmetrical allylic ethers with molybdenum catalysts. We propose likely mechanisms for the observed chemistries.

Iodine catalysed synthesis of unsymmetrical benzylic ethers by direct cross-coupling of alcohols

Although symmetrical ethers can be synthesized easily from alcohols, synthesis of unsymmetrical ethers by dehydrative cross-coupling of alcohols is still a challenge. While dehydrative cross-coupling is environmentally appealing due to formation of water as the only byproduct, the chances for formation of symmetrical ethers always exist. The existing transition metal based methods give good selectivity, but the catalyst are costly and not readily available. Here, we present a simple, readily available, and cost-effective catalyst in the form of molecular iodine which catalyzes a highly selective cross-coupling of benzylic alcohols with benzyl, alkyl, and aryl alcohols to give their corresponding unsymmetrical ethers in good to excellent yield.

Catalytic Reductive Alcohol Etherifications with Carbonyl-Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives.

Ether derivatives have myriad applications in several areas of chemical industry and academia. Hence, the development of more effective and sustainable protocols for their production is highly desired. Among the different methodologies reported for ether synthesis, catalytic reductive alcohol etherifications with carbonyl‐based moieties (aldehydes/ketones and carboxylic acid derivatives) have emerged in the last years as a potential tool. These processes constitute appealing routes for the selective production of both symmetrical and asymmetrical ethers (including O‐heterocycles) with an increased molecular complexity. Likewise, ester‐to‐ether catalytic reductions and hydrogenative alcohol etherifications with CO2 to dialkoxymethanes and other acetals, albeit in less extent, have undergone important advances, too. In this Review, an update of the recent progresses in the area of catalytic reductive alcohol etherifications using carbonyl‐based compounds and CO2 have been described with a special focus on organic synthetic applications and catalyst design. Complementarily, recent progress made in catalytic acetal/ketal‐to‐ether or ester‐to‐ether reductions and other related transformations have been also summarized.

Rapid, chemoselective and mild oxidation protocol for alcohols and ethers with recyclable N-chloro-N-(phenylsulfonyl)benzenesulfonamide

Chlorine is the 20th most abundant element on the earth compared to bromine, iodine, and fluorine, a sulfonimide reagent, N-chloro-N-(phenylsulfonyl)benzenesulfonamide (NCBSI) was identified as a mild and selective oxidant. Without activation, the reagent was proved to oxidize primary and secondary alcohols as well as their symmetrical and mixed ethers to corresponding aldehydes and ketones. With recoverable PS-TEMPO catalyst, selective oxidation over chlorination of primary and secondary alcohols and their ethers with electron-donating substituents was achieved. The reagent precursor of NCBSI was recovered quantitatively and can be reused for synthesizing NCBSI.

Gas-phase etherification of cyclopentanol with methanol to cyclopentyl methyl ether catalyzed by zeolites

Symmetric ethers can be synthesized through the acid-catalyzed self-etherification of biomass-derived alcohols. However, synthesis of asymmetric ethers via catalytic cross-etherification of alcohols is limited by poor selectivity. Herein, we developed an efficient zeolite-catalyzed one-step synthesis of valuable asymmetric cyclopentyl methyl ether (CPME) using gas-phase reaction of bio-based cyclopentanol and methanol. Among different medium- (FER, MCM-22, ZSM-5) and large-pore (BEA, MOR, USY) aluminosilicate zeolites, commercial ZSM-5 catalysts with 2D system of intersecting channels are markedly more selective to CPME. The targeted CPME was produced with a selectivity of 83 % and a yield higher than 80 % over the ZSM-5 catalysts with Si/Al ratios ranging from 15 to 40. Decrease in Si/Al ratio in ZSM-5 enhanced the conversion value, while not affecting the selectivity. FTIR study of the step-by-step adsorption of both reactants in ZSM-5 evidenced the Rideal-Eley mechanism with cyclopentanol adsorbed on acid sites. Therefore, heterogeneously catalyzed gas-phase cross-etherification of renewable cyclopentanol and methanol is a promising process for large-scale applications thanks to its mild operating conditions, high yields and selectivity when using commercial ZSM-5 zeolites as catalysts.