Dimethyl Ether Molecules Research Articles

Heterogeneous Catalysts for Halide-Free Carbonylation of Dimethyl Ether

Acidic cesium salts of 12-tungstophosphoric acid promoted with rhodium, Rh/CsxH3-xPW12O40 (1.5≤x≤2 and Rh≥0.1%), were shown to be novel and effective catalysts for halide-free carbonylation of dimethyl ether (DME) to methyl acetate. The catalysts were characterized by chemical analysis, nitrogen adsorption, XRD, SEM, TGA-DTA and IR spectroscopy. Their behavior may be explained by assuming that (1) activation of the C—O bond in the DME molecule and formation of a metal-alkyl bond occurs in the presence of the strong acid sites and (2) these strong acid sites act in conjunction with Rh carbonyl complexes, which are responsible for CO insertion and acetate formation.

A Dense and Efficient Clathrate Hydrate Structure with Unusual Cages NRCC no: 43877.

Filling space with a host of cages: completely hydrophobic interactions between organic molecules and water are present in the novel clathrate hydrate that has dimethyl ether guests in three different cages. One of these cages is the previously unreported tetrakaidecahedron (4151063) and is shown in the picture along with an ecapsulated dimethyl ether molecule.

An ab initio polarizable intermolecular potential for dimethyl ether: application to liquid simulations

An intermolecular potential for dimethyl ether derived from properties of the monomer and ab initio calculations on the dimer based on an intermolecular perturbation theory is proposed. The interaction energy provided by the potential is a combination of contributions with specific physical significance. The potential was constructed in such a way as to explicitly consider many-body effects, which can be significant in condensed phases. The dimer energies and geometries for the gas phase provided by the potential are quite consistent with the ab initio results. The dispersive term plays a prominent role in most of the minima identified, the electrostatic contribution prevailing only in a single configuration. The results for the trimer reflect a delicate equilibrium between different types of interaction where the dispersive and electrostatic terms prevail in any case. The simulated results for the condensed phase are satisfactorily consistent with both their experimental counterparts and those derived from empirical potentials. In the liquid phase, dimethyl ether molecules cluster in dimers. These occur preferentially in a conformation where the two molecules lie in an antiparallel arrangement in the same plane. The first coordination sphere comprises 13 molecules.

Periodic density functional study on adsorption properties of organic molecules on clean Al (111) surface

The knowledge of the details of an interaction between the metal surface and organic compounds is important in various fields such as catalysis, lubrication, electron chemistry, and so on. As for the lubrication process, the metal–molecule interaction plays an important role in the formation of a protective film on the metal surface. In the present study, the first principle density functional theory (DFT) calculations have been carried out in order to investigate the adsorption properties of various organic molecules on the clean Al surfaces. We have calculated the adsorption energies for methanol, ethylene, ketone, and dimethyl ether molecules, which are widely used in the lubrication field. It has been found that the calculated adsorption energies are in a good agreement with the experimental data. The adsorption energy order of the organic compounds can be presented as follows: methanol>ketone>dimethyl ether>ethylene.

A Three-Center Orbital Interaction in the Diels-Alder Reactions Catalyzed by Lewis Acids.

Ab initio calculations were performed on title reactions between butadiene and acrolein with BCl(3), AlCl(3), GaCl(3), InCl(3), ZnCl(2), SnCl(2), and SnCl(4). A dimethyl ether molecule is explicitly considered in various reaction systems to examine solvent effects. First, the reaction path of an AlCl(3)-promoting reaction was examined thoroughly. This reaction has two channels. The first one involves a weak reactant-like complex (precursor) and a normal [4 + 2] addition. The second does three elementary processes, one-center addition, ring closing, and Claisen shift. The first channel is more favorable by 12.1 kcal/mol (B3LYP/6-311+G(2d,p) SCRF//B3LYP/6-31G SCRF) than the second one. Then the first channels with other Lewis acids were traced with and without an ether molecule. The ether molecule has an appreciable effect not on geometries but on activation energies. BCl(3) is desolvated and has extraordinarily strong catalytic ability. Even with the strongest catalyst, not a [2 + 4] but a normal [4 + 2] cycloaddition takes place. Except for BCl(3), SnCl(4) is the strongest Lewis acid with the ether molecule. The frontier orbital, LUMO, of acrolein is distorted in the course of the reaction so that the formation of two C-C covalent bonds is possible. The precursor formation and the one-center addition were discussed also by the frontier orbital theory.

A Mechanistic Study of the Horner-Wadsworth-Emmons Reaction: Computational Investigation on the Reaction Pass and the Stereochemistry in the Reaction of Lithium Enolate Derived from Trimethyl Phosphonoacetate with Acetaldehyde.

The mechanism of the Horner-Wadsworth-Emmons (HWE) reaction has been investigated using ab initio calculations (RHF/6-31+G). This study revealed that the HWE reaction of the lithium enolate derived from trimethyl phosphonoacetate with acetaldehyde occurs with the addition of the lithium enolate to aldehyde, followed by oxaphosphetane formation, pseudorotation, P-C bond cleavage, and then O-C bond cleavage. The oxaphosphetane formation is the rate-determining step both in the gas phase and in the presence of one dimethyl ether molecule. The transition state leading to trans-olefin is more stable than the transition state leading to cis-olefin. Product selectivity is reproduced by these calculations.

Raman Spectral Evidence of Reactive Oxide Formation during Methanol Oxidation on Polycrystalline Rhodium at High Gas Pressures

Clusters of Pt and Pd catalyze dimethyl ether (DME) combustion to CO2 and H2O at 400–600 K without detectable formation of byproducts. Rh clusters are less active and also form CO, HCHO, and CH3OH in this temperature range. On Pd, isotopic and kinetic studies have shown that DMEO2 reactions proceed via redox cycles limited by hydrogen abstraction from chemisorbed DME molecules without the involvement of methoxide intermediates in kinetically relevant steps, as shown previously on Pt clusters. Kinetic inhibition by H2O is much stronger on Pd than on Pt clusters, apparently because of weaker binding of chemisorbed oxygen (O*) and hydroxyl (OH*) groups on Pt than on Pd. H2O titrates vacancies (*) required to chemisorb DME molecules involved in kinetically relevant H-abstraction steps. DME combustion turnover rates (per exposed metal atom) on Pt, Pd, and Rh increased with increasing cluster size, but were not affected by the identity of the support (Al2O3, ZrO2). These size effects reflect the stronger binding of O* and OH* on smaller clusters, which contain surface atoms with fewer neighbors and greater coordinative unsaturation. The higher reactivity of Pt compared with Pd and Rh also reflects the weaker binding of O* on Pt surfaces and the higher density of vacancies and of DME intermediates interacting with such vacancies. These trends resemble those reported for CH4O2 on Pt and Pd clusters. They represent a general feature of reactions that require vacancies and the abstraction of H-atoms by basic oxygens on surfaces covered predominately by O* or OH* during catalysis.

What Do Ab Initio Calculations Predict for the Structure of Lithiated Azaenolates of Peptides?

AbstractStructures and conformations of the azaenolate lithium salts of amides (formamide, acetamide, and N‐methylacetamide) and of the dipeptide model N‐formylalaninamide were investigated by means of ab initio MO theory. Four possible structures of the lithiated C‐enolates of acetamide were also included in the study. All structures were calculated at the HF/6‐31+G(d) and MP2(fc)/6‐31 + G(d)/HF/6‐31 + G(d) levels; the lithiated azaenolates of formamide were also investigated at higher theoretical levels (up to MP4(fc)/6‐311 + G(d,p)/MP2(fc)/6‐311 + G(d,p)). For the lithiated azaenolates of all amides investigated, the most stable structure contains a four‐membered ring in which the lithium ion is complexed by the oxygen and nitrogen atoms; the substituents attached to the carbon and nitrogen atoms of the azaenolate are in a cis arrangement. The lithiated azaenolates of acetamide are predicted to be more stable than the corresponding C‐enolates. To simulate solvation, calculations on complexes of the lithiated azaenolates of formamide with up to three molecules dimethyl ether were also performed, and all azaenolates of amides were also reoptimized by ab initio reaction‐field calculations. Both solvation models reduce the preference for lithium‐chelated cis structures. The Ramachandran maps of the dilithiated bis(azaenolate) of N‐formylalaninamide (having cis or trans arrangements of the azaenolate substituents) were scanned by MNDO calculations for conformational accessible regions. Thirteen stable structures were subsequently optimized at the HF/6‐31 + G(d) ab initio level. The global minimum resembles a peptide in C7 conformation, but other conformations, not known for peptides, are close in energy. The structures of dimers of the lithiated azaenolates of N‐methylacetamide and of glycinaldehyde were also calculated. The NMR chemical shielding of carbon, nitrogen, and oxygen atoms in all structures were predicted ab initio by using the gauge‐including atomic orbital (GIAO) method.

FT-IR and Quantum Chemical Studies of the Interaction between Dimethyl Ether and HZSM-5 Zeolite

Adsorption of dimethyl ether (DME) on the protonated ZSM-5 zeolite was investigated by FT-IR spectroscopy and density functional theory (DFT) calculation. The coverage and temperature dependencies of characteristic bands and the adsorption on the partially deuterated zeolite were studied by FT-IR. Three bands observed at ca. 2900, 2400, and 1600 cm-1 were ascribed to the bands associated with the Brønsted acidic OH groups hydrogen-bonded to DME, and the band at ca. 3300 cm-1 was assigned to the OH stretching mode of the silanol OH groups hydrogen-bonded to DME. Both the IR and DFT results indicated that DME molecules adsorbed on OH groups by a hydrogen bonding irrespective of the acidity of the OH groups and that the oxonium ions of DME were not produced on the studied surface. The Clausius−Clapeyron plot of the OH stretching band gave the value of −82.4 kJ/mol as ΔH, the energy of adsorption at the acidic site.

Solubility of HFC‐134a refrigerant in glycol‐type compounds: Effects of glycol structure

AbstractEnvironmental concerns have dictated the replacement of CFC‐12 refrigerant with HFC‐134a in automotive air‐conditioning (A/C) systems. Since polyglycols are synthetic compounds compatible with HFC‐134a and considered as lubricants for the A/C compressor, interations of HFC‐134a with glycol‐type compounds and thermodynamic properties of the solutions are important in designing an A/C system. In this work, the solubility of HFC‐134a in four glycol‐type compounds was measured at −5 to 80°C and 90 to 960 kPa. HFC‐134a had the greatest solubility in tetraethylene glycol dimethyl ether. HFC‐134a was less soluble in hexylene glycol and tetraethylene glycol and least soluble in triethylene glycol. Mixtures of HFC‐134a with TRIG or TGDE showed phase separation. Solubility data were used to calculate the activity coefficient of HFC‐134a in glycol solutions. An equation of the form, lnγr = (1 − xr)[A + Bxr], was found to correlate γr to the mole fraction of HFC‐134a in the solution where A and B are constants which may depend on the temperature. Based on a model assuming a specific interaction between molecules and using the activity of HFC‐134a, a higher degree of interaction is expected between HFC‐134a and tetraethylene glycol dimethyl ether molecules than between the molecules of HFC‐134a and other glycols. In general, glycols with free ‐OH groups may have less affinity for HFC‐134a. Solubility is discussed in terms of its parameters and chemical structure of the glycols, as well as the effect of temperature on the solubility, the activity coefficient, and the thermodynamic properties of the HFC‐134a/glycol solutions.

MNDO and ab initio Calculations of Methyl 2-Lithioisobutyrate and Its Solvates and Aggregates

Ab initio and semiempirical (MNDO) molecular orbital calculations are reported of the energies, charge distributions, and geometries of methyl 2-lithioisobutyrate (LIMIB) used as a model of the propagation centre in the anionic polymerization of (meth)acrylates. Two stable forms energetically not very differing were found, one being near to the enolate, the other nearer to the keto form, both at the MNDO and 6-31G** levels. Stabilization energies and geometries of the dimer, trimer, and tetramer aggregates of LIMIB and of its solvates with dimethyl ether molecules were calculated at the MNDO level. These results agree with our earlier experimental findings obtained with the tetrahydrofuran solutions of LIMIB.

Vibrational spectrum and molecular structure of methoxyallene

Infrared and Raman spectra of methoxyallene and its deuteroderivative CD 3 OCHCCH 2 were analysed on the basis of a scaled ab initio force field (4-21G basis set). Scaling factors were transfered from calculations of allene and dimethyl ether molecules in the same basis set. The ab initio force field scaled in this way provides a good agreement of calculated frequencies with experimental ones. Infrared intensities were calculated and compared with experiment. Contrary to vinyl group CH 2 stretching vibration intensities, the intensity of ν s CH 2 of allenyl group is higher than that of ν as CH 2 . This relation is reproduced by ab initio intensities. Both experimental spectra and ab initio calculations show that the local asymmetry of CH 3 group in methoxyallene is the same as in methoxyethene.

A fourier transform ion cyclotron resonance study of the mechanism of formation of protonated dimethyl ether from methanol by use of naturally occurring 18O

AbstractIt is shown that ejection of mass selected ions of high abundance from the cell of a Fourier transform ion cyclotron resonance spectrometer permits the study of ion/molecule reactions of ions of very low abundance. Methanol is used as an illustration. Ejection of all ions with the exception of the 18O labelled protonated methanol molecules, present at natural abundance, shows that the protonated dimethyl ether molecules in this system are formed mainly by an SN2 displacement reaction.

Mechanism of methanol conversion into hydrocarbons over ZSM-5 zeolite

The conversion of methanol into hydrocarbons over ZSM-5 zeolites has been investigated using a gas-recirculation system. The conversion proceeds autocatalytically. The reaction rate is greatly enhanced by the addition of ethylene or cis-but-2-ene, indicating that the autocatalysis is caused by the reaction of olefin and methanol. Infrared studies have revealed that methoxyl groups (—OCD3) are formed by the reaction of surface hydroxyl groups and methanol molecules (CD3OH), and they decompose to reproduce hydroxyl groups (—OD), giving hydrocarbons. The reaction mechanism in which methyl carbonium ions attack the C—H bond of methanol or dimethyl ether molecules is proposed. Methyl carbonium ions are supposed to be released from extensively polarised methoxyl groups formed by the reaction of methanol molecules and strong Brönsted-acid sites. In fact, strongly acidic materials, Nafion H and heteropolyacids, were found effective for methanol conversion. A semiquantitative analysis of the autocatalytic phenomenon in methanol conversion is also presented.

Dissociation of dimethyl ether molecules that is selective for hydrogen, carbon, and oxygen isotopes in the field of a pulsed CO2 laser

Dissociation of dimethyl ether molecules that is selective for hydrogen, carbon, and oxygen isotopes in the field of a pulsed CO2 laser

Primary process(es) in the mercury-photosensitized decomposition of dimethyl ether at 2537 Å

The mercury-photosensitized decomposition of dimethyl ether has been studied at room temperature and at pressures ranging from 10 to 200 Torr.The formation of an excited dimethyl ether (DME) molecule has been verified by following the rates of formation of methane, ethane, and carbon monoxide with various ether pressures.The study of the variation of the quantum yield of molecular hydrogen formation with absorbed light intensity at high ether pressures has shown that the primary process involves the dissociation of ether molecules into hydrogen atoms and methoxy methyl radicals:[Formula: see text]The results presented in this paper indicate that the excited DME molecule can originate in a radical recombination between hydrogen atoms and methoxy methyl radicals.

Stable Configuration of Methyl Groups in Dimethyl Ether

THE internal rotation of a methyl group about its symmetry axis, despite the presence of the group in a great variety of organic molecules, has attracted little attention, probably because experimental methods such as dipole moment measurement, etc., are not available for the elucidation of the problem. In the structural determination of molecules containing methyl groups, each group is often considered as a whole rather than as four separate atoms1. However, the determination is not complete, unless the stable configuration of hydrogen atoms in molecules is taken into account. Recent advances in the experimental technique of electron diffraction by gas molecules have made it possible to determine the values of structural parameters with higher precision than formerly. For the present purpose, a dimethyl ether molecule is perhaps the simplest prototype amenable to the sector-microphotometer method in electron diffraction, because the molecule has non-bonded C … H distances which are sensitive to the rotation of methyl groups and contribute appreciably to the total scattered intensity.

Structures of Dimethyl Ether and Methyl Alcohol

The molecular structures of dimethyl ether and methyl alcohol were determined in gaseous state by means of the sector-microphotometer method in electron diffraction. The structural information was derived from the resolution of radial distribution curves. It was confirmed that a dimethyl ether molecule exerts hindered internal rotation with a potential minimum at the C2v configuration. The most probable values for the bond distances and the bond angles are for dimethyl ether: C–O = 1.416±0.003 A, C–H = 1.094±0.006 A, ∠COC = 111.5°±1.5°; and for methyl alcohol: C–O = 1.428±0.003 A, C–H = 1.095±0.010 A, O–H = 0.960±0.015 A, ∠COH = 109°±3°. The results on methyl alcohol agree with those of microwave determinations. The observed values of vibrational amplitudes are in good agreement with those computed theoretically.

Homogeneous reactions involving complex molecules.—The kinetics of the decomposition of gaseous dimethyl ether

Chemical changes in which molecules of complex structure take part have recently assumed a particular importance in the theory of the mechanism of reaction velocity. Decompositions of organic compounds in the gaseous state provide excellent examples of such reactions. It is often necessary, in these, to suppose the intermediate formation of unstable radicles which undergo rapid subsequent transformations; and whenever each stage of a reaction is not expressed by conventional chemical equations, involving known substances only, there may always remain a slight doubt whether the course of the reaction has been truly represented. Although this does not prevent the drawing of perfectly valid conclusions about the kinetics of a given reaction, nevertheless an example in which every stage can be represented by a simple chemical equation has undoubted advantages. The decomposition of dimethyl ether, with which this paper deals, provides such an example. CH 3 .O.CH 3 → [CH 4 + HCHO] → CH 4 + H 2 + CO. The complexity of the dimethyl ether molecule is only moderate, and in the light of the discussion in the papers referred to above it is interesting to note that the reaction is an almost perfect example of the transition from the unimolecular to the bimolecular type.