Larger Alkyl Research Articles

Enhanced catalytic behavior for methanol to lower olefins over SAPO-34 composited with ZrO2

A microporous SAPO-34 molecular sieve was tailored via a surface compositing strategy of a mesoporous t-ZrO2 with both L acid and base characteristics. A hydrothermal coating method was employed to successfully fabricate the SAPO-34/t-ZrO2 catalyst with a distinct chemical interphase, which showed excellent catalytic activity and lifetime during the conversion of methanol to lower olefins. At ambient pressure and a reaction temperature of 380 °C, the methanol conversion reached 100% and the selectivity for lower olefins was over 90%. The catalyst lifetime reached 1130 min, which was an increase of 770 min compared to using unmodified SAPO-34. By using the physically-blend catalyst t-ZrO2/SAPO-34 and the unmodified SAPO-34 as references, the MTO reaction and carbon deposit behaviors of the surface composited catalyst were determined. Via a hydrothermal coating method to modify the molecular sieve, the fabricated complex solid solution interphase effectively regulated the Si distribution on surface of SAPO-34. The SAPO-34/t-ZrO2 mainly contained synergic active centers of B acid and lesser amounts of L acid-base, as well as a micro-mesoporous system, which were crucial to decrease the carbon deposition formation rate. By studying the in situ IR and carbon deposition, it was revealed that abundant various kinds of active centers and the micro-mesoporous system in the SAPO-34/t-ZrO2 modified catalyst allowed large long-chain alkyl benzenes to form. This novel catalytic behavior effectively inhibited the cyclization and polycondensation of the carbon deposit precursors, leading to an excellent resistance to deactivation induced by carbon deposition.

Decomposition Mechanisms of Di-tert-butylaminoarsane (DTBAA)

III–V semiconductors containing small amounts of nitrogen (“dilute nitrides”) are very promising material systems for optoelectronic applications. Devices based on dilute nitrides currently suffer from problematic C incorporation. To overcome this problem, a novel nitrogen (N) and arsenic (As) precursor for metal–organic vapor phase epitaxy (MOVPE) of the dilute nitride di-tert-butylaminoarsane (DTBAA) has been introduced. DTBAA in comparison to the commonly used 1,1-dimethylhydrazine (UDMHy) showed a significantly improved N incorporation efficiency. The molecule exhibits no strong carbon (C)–N bond, and the C is only present in large alkyl groups which form fewer C radicals since β-H elimination is the dominating decomposition process. This should significantly lower the problematic C incorporation in dilute nitrides and lead to highly efficient devices. To understand the high N incorporation efficiency as well as the As incorporation, the gas-phase decomposition of this novel precursor has been studied with a real time Fourier transform (FT) quadrupole ion trap mass spectrometer (iTrap) from Carl Zeiss SMT GmbH in a horizontal Aixtron Aix 200 GFR MOVPE reactor. Formation of isobutane and isobutene proves a radical cleavage and β-H-elimination as decomposition processes of the tert-butyl groups attached to the molecule. Furthermore, the appearance of ammonia (NH3) has been detected. This indicates a direct cleavage of the As–N bond of the molecule, resulting in the formation of an aminyl radical (NH2•). The formation of NH2• explains the high N incorporation efficiency of DTBAA as well as its limitations due to desorption of NH3 at higher temperatures.

Friction and Wear Behavior of Environmentally Friendly Ionic Liquids for Sustainability of Biolubricants

The sustainability of biolubricants as green alternatives for industrial and machinery lubrication is questionable due to their unreliable oxidative stability, high pour point, and easy accumulation of contaminants that affect their tribological performance. Bio-based ionic liquid (IL) lubricants, which are environmentally friendly liquid state salts, have overcome these concerns related to conventional biolubricants. The present study investigates the effect of varying cation–anion moieties in ILs to understand their tribological performance and industrial viability. The industrial viability was analyzed by scaling their friction and wear behaviors against conventional biolubricants, and petroleum-based oils. The study investigated both bio- and nonbio-based ILs. Among the ILs examined, P666,14Saccharinate, P666,14Salicyate, and P666,14Benzoate were found to have superior tribological properties. The presence of large alkyl cation chain length and large aromatic anion ring size in ILs can effectively reduce friction and wear. This study details the mechanism by which the structural combinations of anion and cation in ILs define the tribological behavior of the bulk IL. Additionally, this study also highlights the environmentally benign nature of IL lubricants for possible industrial applications.

Probing the Interactions of 1-Alkyl-3-methylimidazolium Tetrafluoroborate (Alkyl = Octyl, Hexyl, Butyl, and Ethyl) Ionic Liquids with Bovine Serum Albumin: An Alkyl Chain Length-Dependent Study.

Herein, we have investigated the binding interaction of bovine serum albumin (BSA) with a series of 1-alkyl-3-methylimidazolium tetrafluoroborate (alkyl = ethyl, butyl, hexyl, and octyl) ionic liquids (ILs) in physiological buffer medium. The ILs are chosen basically to understand the effect of alkyl chain length on IL-protein interaction. Experiments have shown that the quenching of fluorescence of BSA is induced by relatively longer alkyl chain-containing ILs, [OMIM][BF4] and [HMIM][BF4]. The enthalpy-driven spontaneous binding (-ve Δ G) of hexyl and octyl chain-containing ILs with the protein is mediated by both hydrogen-bonding and van der Waals interactions. The experimental data have categorically explained the denaturation of protein conformation upon interaction with both [OMIM][BF4] and [HMIM][BF4]. The molecular docking calculation nicely corroborates the experimentally obtained results. The present study reveals that neither a smaller alkyl group-containing IL nor a very large alkyl group-containing IL is necessary to have effective protein-IL interactions. The study also reveals the influence of hydrophobic interaction over and above the hydrogen-bonding interaction on protein-IL binding events and essentially gives an idea about the optimum hydrophobic character of the ILs that is necessary to induce protein-IL interaction and consequently the denaturation of the protein structure.

Study of effective geometry parameter, order parameter, temperature gradients and crossover temperatures of three nematic liquid crystals having highly different clearing temperature

The temperature dependent properties of three liquid crystals (LC) namely effective geometry parameter, order parameter and temperature gradients of refractive indices of two fluorinated isothiocyanato nematic liquid crystal (NLC) compounds 4′-pentylcyclohexyl-3,5-difluoro-4-isothiocyanatobiphenyl, 4'−butylcyclohexyl−3, 5− difluoro− 4− isothiocyanato-biphenyl of high clearing temperature (TC) and low TC LC compound 4 (trans-4/-n-hexycyclohexyl) isothiocyanatobenzene (6CHBT) have been studied. In this paper, the effective geometry parameters of the three LC compounds are calculated. The order parameters of three LC compounds are also calculated from the effective geometry parameter. From the available data, it is found that the two fluorinated NLC compounds exhibit moderately high value of birefringence (∼0.24–0.26) and 6CHBT exhibits a lower value of birefringence (∼0.16). From the study, it is found that the order parameter is found to be higher in higher birefringence and higher TC LC compounds. The values of temperature gradient of ordinary refractive index (dno/dT) are found to be showing negative to positive value while increasing temperature which gives the crossover temperature (TCO). The crossover temperature has been calculated from the temperature gradient at the value (dno/dT) = 0. LC compounds with lower TC are found to have larger TCO value which gives narrower temperature between TCO and TC. The TCO value of compound having larger alkyl group is found to be smaller. The Lorentz field factors for both compound are also reported which can be used for order parameter calculation by different aspects.

Prediction of the phase equilibria for island-type asphaltenes via HMC-WL simulations.

Recent force microscopy experiments have shed light on new possible molecular structures for asphaltenes, which are key compounds for the oil industry. These studies have revealed the significance of asphaltenes with an island molecular architecture, i.e., composed of a large polycyclic aromatic hydrocarbon (PAH) core and alkyl side chains. In this work, we carry out molecular simulations based on a Wang-Landau sampling of the isothermal-isobaric ensemble to determine the thermodynamic properties of island-type asphaltenes at the vapor-liquid coexistence. We first parameterize a coarse-grained force field for these systems, focusing on compounds with a PAH core containing fluorene, fluoranthene, and dibenzothiophene motifs. Then, using this coarse-grained force field, we predict the entire phase envelope, including the boiling points and the critical parameters for a series of island-type asphaltenes.

Ionic liquids at the surface of graphite: Wettability and structure.

The aim of this work is to provide a better understanding of the interface between graphite and different molecular and ionic liquids. Experimental measurements of the liquid surface tension and of the graphite-liquid contact angle for sixteen ionic liquids and three molecular liquids are reported. These experimental values allowed the calculation of the solid/liquid interfacial energy that varies, for the ionic liquids studied, between 14.5 mN m-1 for 1-ethyl-3-methylimidazolium dicyanamide and 37.8 mN m-1 for 3-dodecyl-1-(naphthalen-1-yl)-1H-imidazol-3-ium tetrafluoroborate. Imidazolium-based ionic liquids with large alkyl side-chains or functionalized with benzyl groups seem to interact more favourably with freshly peeled graphite surfaces. Even if the interfacial energy seems a good descriptor to assess the affinity of a liquid for a carbon-based solid material, we conclude that both the surface tension of the liquid and the contact angle between the liquid and the solid can be significant. Molecular dynamics simulations were used to investigate the ordering of the ions near the graphite surface. We conclude that the presence of large alkyl side-chains in the cations increases the ordering of ions at the graphite surface. Benzyl functional groups in the cations lead to a large affinity towards the graphite surface.

Poly(arylene ether ketone) Copolymer Grafted with Amine Groups Containing a Long Alkyl Chain by Chloroacetylation for Improved Alkaline Stability and Conductivity of Anion Exchange Membrane

We report simple and controllable acetylation of poly(arylene ether ketone) (PK) followed by Menshutkin reaction (quaternization), to prepare a highly alkaline stable and conductive (phase-separated) anion exchange membrane (AEM). A long side alkyl chain grafted with ammonium groups facilitates decent hydrophilic/hydrophobic microphase separation. Prepared AEMs exhibited improved conductivity, alkaline stability, and water resistivity, because of well-designed membrane architecture. Under alkaline conditions, nucleophilic substitution reaction and/or Hofmann elimination reaction (β-hydrogen) are expected to protected by grafting of a large volumetric alkyl chain (C = 16) with amine groups responsible for steric hindrance. Suitably assessed PK-QD-48 AEM reveals 0.81 V open circuit voltage (OCV) corresponding to 25.53 mW cm–2 power density at 65 °C in alkaline direct methanol fuel cell (ADMFC) operation. The reported synthetic strategy offers a novel route for preparing highly conducting, and alkaline stabl...

Influence of Tetra Alkyl Ammonium Cation on Thermo-Physical Properties of N,N-Dimethyl Formamide with 1,4-Dioxane at Different Temperatures

Ultrasonic technique, transport properties and related acoustical parameters of 1,4-dioxane and N,N-dimethyl formamide were prepared of different % compositions at variable temperatures using tetra alkyl ammonium iodide salts (R4NI) of 0.14 M, to investigate inter-ionic interactions, molecular interactions, molecular rearrangement, molecular association etc. The densities were measured by using magnetic float densitometer. Transport properties provide a deep and meaningful insight of various interactions taking place between the binary liquid mixtures with salts. We have observed the influence of small as well as large alkyl chain length (R4N+), and extract the information with respect to various kinds of intermolecular interactions such as dipole-dipole, dipole-induced dipole, solute-solvent, dispersive type and H-bonding interaction between the components. Such observations in the presence of specific molecular interactions of binary solutions and structural effects were analyzed on the basis of measured and derived thermo-dynamical parameters.

Mutagenesis of Met-151 and Thr-153 to alanine in Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase changes substrate specificity for acetophenones.

Secondary alcohol dehydrogenase (SADH) from Thermoanaerobacter ethanolicus reduces ketones to chiral alcohols, and generally obeys Prelog's Rule, with binding pockets for large and small alkyl substituents, giving (S)-alcohols. We have previously shown that mutations in both the large and small pockets can alter both substrate specificity and stereoselectivity. In the present work, Met-151 and Thr-153, residues located in the small pocket, were mutated to alanine. The M151A mutant SADH shows significantly lower activity and lower stereoselectivity for reduction of aliphatic ketones than wild-type SADH. Furthermore, M151A showed non-linear kinetics for reduction of acetone. T153A SADH shows lower activity but similar stereoselectivity for ketone reduction compared to wild-type SADH. The I86A/M151A/C295A and I86A/T153A/C295A triple mutant SADH show altered specificity for reduction of substituted acetophenones. These results confirm that these mutations are useful to combine with I86A/C295A SADH to expand the small pocket of SADH and broaden the substrate specificity.

Highly selective methanol-to-olefin reaction on pyridine modified H-mordenite

The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO (methanol to olefin) reactions were investigated. The catalytic analysis demonstrates that the pyridine modified MOR zeolite yielded high selectivity (> 65.3%) of C2=-C4=, although the conversion dropped from 100% to 54%. Furthermore, both the catalytic lifetime of MOR and the stability of yielding the lower olefins were increased from less than 30min to more than 120min after the modification with pyridine. 1H MAS NMR on MOR and modified MOR shows that the acid sites in main channel do not benefit the productivity of lower olefins and catalysts’ lifetime. It can be concluded from ex-situ 13C CP MAS NMR that the deposit species during the MTO reaction depend on the pore sizes, and the formation of large alkyl aromatic species more likely occurs in the 12-ring main channels rather than the 8-ring side pocket.

Study of the Influence of Alkyl Chain Cation Solvent Interactions on the Slope of ϕv v/s √C Curves in 1, 3-Butanediol-DMF Solvent Mixtures by Apparent Molar Volume Measurements

The concept of Frank's hypothesis (that is the effect of large tetra alkyl ammonium ions on the solvent structure, especially water, in the ion-ion and ion-solvent interactions) was found to be not applicable when water was replaced by one of the organic solvents e.g. Dimethyl formamide (DMF), in the solvent mixture, that is, if the study involves ion-ion and ion- solvent interactions in 1,5-pentane diol - DMF solvent mixture containing large cations of tetraalkyl ammonium iodides. The densities of binary solvent mixtures and salt solutions have been measured at 298.15 K by magnetic float densitometer. The apparent molar volumes at infinite dilution, ФV 0 , determined by ФV -values in the solvent mixtures, have been utilized to estimate the partial molar volumes of transfer, ΔФV 0 (tr), for various tetraalkyl ammonium iodide salts from DMF to 1,5-Pentane diol.

Controlling Selectivity by Controlling Energy Partitioning in a Thermal Reaction in Solution

The comparison of experimental and predicted kinetic isotope effects in the α-cleavage of alkoxy radicals is used here to judge the applicability of statistical rate theories. It is found that the governing rate theory and the statistical versus nonstatistical nature of the cleavage depend on the cleavage barrier and how much energy is imparted to the radical. The latter can then be controlled by changing the size of substituents in the system. With a large alkyl group substituent, the vibrational energy of the alkoxy radical is increased, but this energy is not statistically distributed, leading to a lower isotope effect than predicted by statistical theories. The observed isotope effect can be approximately rationalized using a semistatistical localized RRKM model.

A study of the molecular interactions between ammonium-based ionic liquids and N,N-dimethylacetamide

In this work, we report the molecular interactions of different cation alkyl chain lengths with same anion of ammonium-based ionic liquids (ILs) such as tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) with N,N-dimethylacetamide (DMA) through thermophysical properties with varying the compositions of ILs at different temperatures from 25 to 40°C under atmospheric pressure. Experimental densities (ρ), ultrasonic sound velocities (u), viscosities (η) and refractive indices (nD) of binary mixtures of ILs with DMA are measured over the wide composition range. The excess molar volumes (VE), deviation in isentropic compressibilities (Δκs), deviation in viscosities (Δη) and deviation in refractive indices (ΔnD) are calculated from experimental values and are correlated by Redlich-Kister polynomial equations. Consequently, VE values show that negative for small cation alkyl chain length of ammonium-based ILs as compared to large cation alkyl chain length of ILs. We have observed the strength of intermolecular interactions such as hydrogen bonding, ion-ion pair interactions and induced dipole interactions between the ions of ammonium-based ILs with DMA from obtained data. Thermophysical properties, however, possessed by these binary systems are exceedingly promising and predictable that these systems will find applications in chemical industry.

Distance-Dependent Attractive and Repulsive Interactions of Bulky Alkyl Groups.

The stabilizing and destabilizing effects of alkyl groups on an aromatic stacking interaction were experimentally measured in solution. The size (Me, Et, iPr, and tBu) and position (meta and para) of the alkyl groups were varied in a molecular balance model system designed to measure the strength of an intramolecular aromatic interaction. Opposite stability trends were observed for alkyl substituents at different positions on the aromatic rings. At the closer meta-position, smaller groups were stabilizing and larger groups were destabilizing. Conversely, at the farther para-position, the larger alkyl groups were systematically more stabilizing with the bulky tBu group forming the strongest stabilizing interaction. X-ray crystal structures showed that the stabilizing interactions of the small meta-alkyl and large para-alkyl groups were due to their similar distances and van der Waals contact areas with the edge of opposing aromatic ring.

Distance‐Dependent Attractive and Repulsive Interactions of Bulky Alkyl Groups

AbstractThe stabilizing and destabilizing effects of alkyl groups on an aromatic stacking interaction were experimentally measured in solution. The size (Me, Et, iPr, and tBu) and position (meta and para) of the alkyl groups were varied in a molecular balance model system designed to measure the strength of an intramolecular aromatic interaction. Opposite stability trends were observed for alkyl substituents at different positions on the aromatic rings. At the closer meta‐position, smaller groups were stabilizing and larger groups were destabilizing. Conversely, at the farther para‐position, the larger alkyl groups were systematically more stabilizing with the bulky tBu group forming the strongest stabilizing interaction. X‐ray crystal structures showed that the stabilizing interactions of the small meta‐alkyl and large para‐alkyl groups were due to their similar distances and van der Waals contact areas with the edge of opposing aromatic ring.

Preparation and characterisation of novel cross-linked poly (IBOMA-BA-DFMA) latex

Purpose – The purpose of this research was to synthesize a novel cross-linked latex copolymerised by butyl acrylate (BA), isobornyl methacrylate (IBOMA), hydroxy propyl methacrylate (HPMA) and dodecafluoroheptyl methacrylate (DFMA). IBOMA is a very useful functional monomer. Its molecular structure not only contains bornyl acetate alkoxy but also includes a double bond, which can be copolymerised with other unsaturated monomers via free radical polymerization. The large nonpolar bicyclic alkyl in bornyl acetate alkoxy offers the polymer chain strong space steric protection, which endows the polymer with some special properties. Design/methodology/approach – The semi-continuous seeded emulsion polymerisation technology was adopted to copolymerise BA, IBOMA, HPMA and DFMA in the water phase, which was initiated with potassium persulfate (KPS) and emulsified with the mixed surfactants of sodium dodecyl sulphate (SDS) and OP-10. Findings – The particle size of the latex decreases with an increase in the amount of IBOMA. All the latexes have good mechanical stability and calcium ion stability. The latex has good film-forming property when the IBOMA amount is controlled moderately. The optimal IBOMA amount is 10.00 g. The thermal stability and water resistance of the film are improved. Practical implications – The latexes can be applied as a binder of coatings and adhesions. Originality/value – The effect of the amount of IBOMA and BA on the properties of the resultant latex and its film were investigated in detail. In comparison with the latexes copolymerised without IBOMA, the novel latex has better thermal stability and water resistance.

Radical Reactivity in the Condensed Phase: Intermolecular versus Intramolecular Reactions of Alkoxy Radicals.

Condensed-phase alkoxy (RO) radicals can undergo unimolecular (e.g., intramolecular H atom abstraction) reactions as well as bimolecular (intermolecular H atom abstraction) reactions, though the competition between these two channels is not well constrained. Here, we examine this branching by generating RO radicals from the photolysis of a large alkyl nitrite (C20H41ONO) in hexanes and nebulizing the mixture into an aerosol mass spectrometer for analysis. Product ions associated with unimolecular (isomerization) reactions were observed to increase upon photolysis. However, no formation of the C20 alcohol (C20H41OH, the expected product from RO + RH reactions) was observed, suggesting that bimolecular reactions are at most a minor channel for this condensed-phase system (involving saturated hydrocarbons). This result, combined with previous studies of liquid-phase RO radicals carried out at higher concentrations, suggests that when 1,5-H atom abstraction reactions are facile (i.e., in which a 1,5-H atom shift from a secondary or tertiary carbon can occur), this channel will dominate over bimolecular reactions.

Properties and bioavailability of particulate and mineral‐associated organic matter in Arctic permafrost soils, Lower Kolyma Region, Russia

SummaryPermafrost degradation may cause strong feedbacks of arctic ecosystems to global warming, but this will depend on if, and to what extent, organic matter (OM) is protected against biodegradation by mechanisms other than freezing and anoxia. Here, we report on the amount, chemical composition and bioavailability of particulate (POM) and mineral‐associated OM (MOM) in permafrost soils of the East Siberian Arctic. The average total organic carbon (OC) stock across all soils was 24.0 ± 6.7 kg m−2 within 100 cm soil depth. Density fractionation (density cut‐off 1.6 g cm−3) revealed that 54 ± 16% of the total soil OC and 64 ± 18% of OC in subsoil horizons was bound to minerals. As well as sorption of OM to clay‐sized minerals (R2 = 0.80; P < 0.01), co‐precipitation of OM with hydrolyzable metals may also transfer carbon into the mineral‐bound fraction. Carbon:nitrogen ratios, stable carbon and nitrogen isotopes, 13C‐NMR and X‐ray photoelectron spectroscopy showed that OM is transformed in permafrost soils, which is a prerequisite for the formation of mineral‐organic associations. Mineral‐associated OM in deeper soil was enriched in 13C and 15N, and had narrow C:N and large alkyl C:(O‐/N‐alkyl C) ratios, indicating an advanced stage of decomposition. Despite being up to several thousands of years old, when incubated under favourable conditions (60% water‐holding capacity, 15°C, adequate nutrients, 90 days), only 1.5–5% of the mineral‐associated OC was released as CO2. In the topsoils, POM had the largest mineralization but was even less bioavailable than the MOM in subsoil horizons. Our results suggest that the formation of mineral‐organic associations acts as an important additional factor in the stabilization of OM in permafrost soils. Although the majority of MOM was not prone to decomposition under favourable conditions, mineral‐organic associations host a readily accessible carbon fraction, which may actively participate in ecosystem carbon exchange.

Phase behavior of the surfactant ionic liquid trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate with water and dodecane

Abstract Trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate is a surface-active room temperature ionic liquid: it is an ionic component, liquid at room temperature, and also a surfactant due to the presence of large (hydrophobic) alkyl chains attached to an ionic moiety. Moreover, since both the anion and the cation have large alkyl chains, both ions have surface active character, what has been called a catanionic or biamphiphillic surfactant. In this work, the surfactant has been characterized through the measurement of the critical micelle concentration in aqueous solutions and related parameters. The phase diagram for ternary mixtures with water and n-dodecane has been determined, showing a Winsor type III behavior. The effect of temperature and amphiphile concentration on the ternary system has been studied with fish diagrams. A large effect of temperature on the phase diagram has been found, with the existence of a triphasic region from 278 up to 305 K. Interfacial tension between equilibrium phases has been measured experimentally for the ternary system, using either pure water or 4 wt% NaCl brine. Density and viscosity of the involved phases have also been measured as valuable information in oil recovery. Results obtained are discussed in terms of the validity of this surfactant for this application.