Tetramethylethylene Research Articles

An experimental and modeling study of tetramethyl ethylene pyrolysis with polycyclic aromatic hydrocarbon formation

Iso-olefins, in the C5–C8 range can potentially be blended with renewable gasoline fuels to increase their research octane number (RON) and octane sensitivity (S). RON and S increase with the degree of branching in iso-olefins and this is a desirable fuel anti-knock quality in modern spark-ignited direct-injection engines. However, these iso-olefins tend to form larger concentrations of aromatic species leading to the formation of polycyclic aromatic hydrocarbons (PAHs). Thus, it is important to understand the pyrolysis chemistry of these iso-olefins. In this study, a new detailed chemical kinetic mechanism is developed to describe the pyrolysis of tetramethyl ethylene (TME), a symmetric iso-olefin. The mechanism, which includes the formation of PAHs, is validated against species versus temperature (700–1160 K) measurements in a jet-stirred reactor at atmospheric pressure and in a single-pulse shock tube at a pressure of 5 bar in the temperature range 1150–1600 K. Synchrotron vacuum ultraviolet photoionization mass spectrometer (SVUV-PIMS) and gas chromatography (GC) systems were used to quantify the species in the jet-stirred reactor and in the single-pulse shock tube, respectively. The mechanism derives its base and PAH chemistry from the LLNL PAH sub-mechanism. The predictions are accurate for most of the species measured in both facilities. However, there is scope for mechanism improvement by understanding the consumption pathways for some of the intermediate species such as isoprene. The formation of 1, 2, and 3-ring aromatic species such as benzene, toluene, naphthalene and phenanthrene measured experimentally is analyzed using the chemical kinetic mechanism. It is found that the PAH formation chemistry for TME under pyrolysis conditions is driven by both propargyl addition reactions and the HACA mechanism.

A combustion chemistry study of tetramethylethylene in a laminar premixed low-pressure hydrogen flame

The combustion chemistry of tetramethylethylene (TME) was studied in a premixed laminar low-pressure hydrogen flame by combined photoionization molecular-beam mass spectrometry (PI-MBMS) and photoelectron photoion coincidence (PEPICO) spectroscopy at the Swiss Light Source (SLS) of the Paul Scherrer Institute in Villigen, Switzerland. This hexene isomer with the chemical formula C6H12 has a special structure with only allylic CH bonds. Several combustion intermediate species were identified by their photoionization and threshold photoelectron spectra, respectively. The experimental mole fraction profiles were compared to modeling results from a recently published kinetic reaction mechanism that includes a TME sub-mechanism to describe the TME/H2 flame structure. The first stable intermediate species formed early in the flame front during the combustion of TME are 2-methyl-2-butene (C5H10) at a mass-to-charge ratio (m/z) of 70, 2,3-dimethylbutane (C6H14) at m/z 86, and 3-methyl-1,2-butadiene (C5H8) at m/z 68. Isobutene (C4H8) is also a dominant intermediate in the combustion of TME and results from consumption of 2-methyl-2-butene. In addition to these hydrocarbons, some oxygenated species are formed due to low-temperature combustion chemistry in the consumption pathway of TME under the investigated flame conditions.

The INNpinJeR: a new wall-free reactor for studying gas-phase reactions

The Innsbruck wall free impinging jets reactor (INNpinJeR) is characterized by quantifying oxidation products of the well-understood ozonolysis reactions of tetramethyl ethylene and cyclohexene with an ammonium chemical ionization mass spectrometer.

Solvent Effect on Assembling and Interactions in Solutions of Phenol: Infrared Spectroscopic and Density Functional Theory Study.

This work provides new insight into assembling of phenol in various solvents and competition between different kinds of interactions. To examine both weak and strong interactions, we selected a series of non-aromatic and aromatic solvents. Infrared spectra were measured at low (0.05 M) and high (2 M) phenol content. In addition, we performed density functional theory calculations of the structures and harmonic vibrational spectra of 1:1 complexes of phenol with the solvents and the associates of phenol from dimer to tetramer. Based on these results, we divided the solvents into three groups. The first group consists of non-aromatic solvents weakly interacting with phenol. Depending on the concentration, molecules of phenol in these solvents remain non-bonded or self-associated. In diluted solutions of phenol in chlorinated non-aromatic solvents do not appear free OH groups, since they are involved in a weak OH···Cl interaction. It is of note that in diluted solutions of phenol in tetramethyl ethylene both the non-bonded and bonded OH coexists due to solvent-solvent interactions. The second group consists of aromatic solvents with methyl or chlorine substituents. At low concentration, the molecules of phenol are involved in the phenol-solvent OH···π interaction and the strength of these interactions depends on the solvent properties. At a higher phenol content an equilibrium exists between phenol-solvent OH···π and phenol-phenol OH···OH interactions. Finally, the third group includes the aromatic and non-aromatic solvents with highly polar group (C≡N). In these solvents, regardless of the concentration all molecules of phenol are involved in the solute-solvent OH···NC interaction. Comparison of the experimental and theoretical band parameters reveals that molecules of phenol in non-aromatic solvents prefer the cyclic associates, while in the aromatic solvents they tend to form the linear associates.

Selective Photochemical Reaction by Fixing Reactant as a MOF Building Block

We demonstrate selective photo-reactions observed between the two different chemical species bearing carbon-carbon double bonds in MOF 1. 1,2-Bis(4-pyridyl)ethylene (bpe) was fixed in 1 as the organic linker, which reacted with tetramethylethylene (TME) as the guest molecule. As a result, a specific product from the radical reaction was selectively generated, whereas various side products were observed when reacted in solution. Our strategy to realize selective reactions would contribute to enforce the applicability of solid-phase reactions in synthetic chemistry.

Preparation of De-emulsifier of Gemini Surfactant & it's Application in Oil Industry

A Gemini surfactants (GS) which are bis quaternary ammonium salt. It is prepared from tetramethyl ethylene diamine (TMEDA) with cetyl bromide, while an ordinary surfactant (OS),which is quaternary ammonium salt, is prepared from trimethyl amine (TMA) and cetyl bromide. They were identified by elemental analysis and IR spectroscopy.
 Comparing the GS,OS and the commercial surfactants, the Gemini surfactant shows an interesting properties and have a variety of uses, such as a De-emulsifier.
 Adopting the composition ratios found in the study of reverse chemistry of commercial De-emulsifier, Rp 6000, which is usually use in the south and north oil companies in Iraq. The prepares active gradients were characterized by various techniques, IR spectroscopy, elemental analysis, melting point, solubility, flash point and functional group analysis.
 
 The efficiency of the prepared De-emulsifier was examined by standard methods and compared with the efficiency of commercial Rp 6000 based on the same wet crude oil sources.

Transient species in the ozonolysis of tetramethylethene

The reaction of alkenes with ozone has great effect on atmospheric oxidation, its transient species can produce OH radicals and contribute to the formation of secondary organic aerosols (SOA). In the present study, the reaction of tetramethylethene (TME) with ozone was investigated using self-assembled low temperature matrix isolation system. The TME and ozone were co-deposited on a salt plate at 15 K, and then slowly warmed up the plate. The first transient species primary ozonide (POZ) was detected, indicating that the reaction followed Criegee mechanism. Then POZ began to decompose at 180 K. However, secondary ozonide (SOZ) was not observed according to Criegee mechanism. Probably, Criegee Intermediate (CI) did not react with inert carbonyl of acetone, but with remaining TME formed tetra-methyl epoxide (EPO).

Permanganyl chloride-mediated oxidation of tetramethylethylene: A density functional theory study

The mechanisms of the oxidation of tetramethylethylene (TME) by permanganyl chloride (MnO3Cl) have been explored on the singlet and triplet potential energy surfaces at the B3LYP LANL2DZ/6-31G (d) level of theory. The results show that the pathway leading to the formation of the five-membered dioxylate through concerted [3 + 2] addition is favored kinetically and thermodynamically over the three other possible pathways, namely the [2 + 2] addition via the transient metallaoxetane intermediate, epoxidation, and hydrogen transfer pathways. The epoxide precursor that on hydrolysis would yield the epoxide product will most likely arise from a stepwise path through the intermediacy of an organometallic intermediate. This pathway affords the product that is more stable (thermodynamically favorable). However, kinetically, both the stepwise and the concerted [2 + 1] addition pathways leading to the epoxide precursors are very competitive (activation barrier difference of <0.7 kcal/mol).

DFT and TDDFT study of chemical reactivity and spectroscopic properties of M(TePh)2 [TMEDA] M=Zn, Cd, and Hg complexes

A series of complexes of the type M(TePh)2 [TMEDA], where M = Zn, Cd, or Hg and TMEDA: N, N′, N′-tetra methyl ethylene diamine, have been investigated by the means of density functional theory (DFT) and time-dependent density functional theory (TDDFT) with LANL2DZ basis set. The geometric parameters, related energies, spectroscopic properties, namely, infrared and UV–visible spectra, and reactivity descriptors of these complexes were computed. The calculated values of the structural parameters show a good agreement with the available experimental data. The calculation of the reactivity descriptors confirm that the complex Zn (TePh)2 [TMEDA] is the most active biologically. The latter is of potential medical importance, mainly due to the presence of zinc, which is required for proper functioning of human biological systems. The frequencies of metal-Te, in the infrared spectra, are in the terahertz region, which find applications in multitude of areas in science and engineering, ranging from imaging tissue in medicine to security systems. The wavelengths, in the UV–visible spectra, are in near ultraviolet and visible regions. Three types of charge transfer are distinguished: intra-ligands, metal–ligand, and ligand–metal charge transfers.

Montmorillonite-based polyacrylamide hydrogel rings for controlled vaginal drug delivery.

Vaginal drug delivery is regarded as a promising route against women-related health issues such as unwanted pregnancies and sexually transmitted infections. However, only a very few studies have been reported on the use of hydrogel rings with low cytotoxicity for vaginal drug delivery applications. Moreover, the effect of nanoparticles on hydrogel vaginal rings has not been clearly evaluated. To overcome these challenges, we hereby developed nanocomposite hydrogel rings based on polyacrylamide-sodium carboxymethyl cellulose-montmorillonite nanoparticles in the ring-shaped aluminum mold for controlled drug delivery. The hydrogel rings were synthesized by using N,N'-methylene bisacrylamide, N,N,N',N'-tetramethyl ethylene diamine, and ammonium persulfate, as a crosslinker, accelerator, and initiator, respectively. The obtained rings were 5.5cm in diameters and 0.5cm in rims. Chemical structures of the nanocomposite rings were confirmed by Fourier transform infrared, and Nuclear Magnetic Resonance spectroscopies. Additionally, the swelling ratio of hydrogels was appeared to be adjusted by the introduction of nanoparticles. In vitro release experiment of methylene blue, as a hydrophilic model drug, revealed that the nanocomposite rings could not only reduce burst effect (almost more than twice), but also achieve prolonged release for 15days in the vaginal fluid simulant which mimic the vaginal conditions at pH of almost 4.2, and a temperature of 37°C. Importantly, the resultant hydrogel rings with or without various concentrations of montmorillonite showed low cytotoxicity toward human skin fibroblasts. Furthermore, different antibacterial activities against Escherichia coli were observed for various concentrations of montmorillonite in hydrogels. These results suggest the great potential of montmorillonite-based hydrogel rings for vaginal drug delivery.

Synthesis and characterization of a ROMP-based polycationic antimicrobial hydrogel

This study has investigated the antimicrobial potential of ring opening metathesis polymerization (ROMP)-based hydrogels. Initially, double charge containing cationic (DABCO)-ROMP polymers were synthesized and characterized. Subsequently, DABCO-ROMP polymer was added into a hydrogel formulation comprised of acrylamide (AAm), N,N'-methylenebis(acrylamide) (BAAm) and/or poly(ethylene glycol) diacrylate (PEG diacrylate, Mn = 700 g/mol) in different quantities to investigate the antimicrobial efficiency of the hydrogel formulations. N,N,N′,N′-tetramethyl ethylene diamine (TEMED) is used with ammonium persulfate (APS) to catalyze polymerization in water. The structures of the resulting hydrogels were characterized using infrared spectroscopy (IR). The cross-linking properties and surface morphologies were investigated via the swelling behavior and scanning electron spectroscopy (SEM). Fluorescein (Na salt) staining measurements were also used to analyze the positive charge density of the hydrogels. The antimicrobial hydrogels showed excellent antimicrobial efficacy against Escherichia coli (E. coli, ATCC 25922), Staphylococcus aureus (S. aureus, ATCC 29213) and Candida albicans (C. albicans, ATCC 90028). It was observed that the cationic ROMP polymer in the hydrogel formulation played a crucial role in the biocidal activity. Furthermore, cytotoxicity studies on human umbilical vein endothelial cells (HUVEC) and tetrazolium salt assay (MTS) cell lines were also performed on the hydrogels and the most potent copolymer revealed no cytotoxicity. Therefore, the ROMP-based hydrogels show good biocidal properties with potential applications in various biomedical fields.

Preparation and characterisation of nano enhanced phase change material by adding carbon nano tubes to butyl stearate

A nano enhanced phase change material, NEPCM, was prepared by the addition of carbon nanotubes, CNTs, to butyl stearate. This study utilised single walled nano tube, multi-walled nanotube and modified multi-walled nanotube. Several kinds of surfactants were used to stabilise nano-particles in butyl stearate. Tetramethyl ethylene diamine (TEMED) was the best surfactant for enhancing the stability time of nano-fluid. The effect of CNTs concentration on the thermal properties of base fluid was studied and it was found that for all kinds of CNTs, the highest thermal conductivity of NEPCM was observed in weight fraction of 0.03. The modified-MWCNTs have the most enhancements in the butyl stearate thermal conductivity. It was found from differential scanning calorimetry tests, that modified-MWCNTs with 2 wt.% contents have the most effect on the latent heat of fusion of the base fluid. It was also observed that the SWCNT has a considerable effect on the melting point of PCM.

Novel metronidazole-loaded hydrogel as a gastroretentive drug delivery system

A metronidazole-loaded hydrogel was synthesized by free radical polymerization using dimethylaminoethyl methacrylate (DMAEMA) monomer and triethyleneglycol dimethacrylate (TEGDA) and methylene bisacrylamide (MBA) as cross-linkers. The DMAEMA hydrogels were cross-linked with 5 and 10% MBA or with 0.1, 0.5, 1 and 4% TEGDA as cross-linking agents. Ammonium persulfate and tetramethyl ethylene diamine were used as initiator and catalyst, respectively. The prepared hydrogels were characterized, and the effect of cross-linking agent content on the swelling behavior and in vitro drug release of hydrogels was investigated. The results of X-ray diffractometry, differential scanning calorimetry and Fourier transform infrared spectroscopy studies indicated that the prepared hydrogels possessed an amorphous morphology and there was not any interaction between the hydrogel polymers and metronidazole as drug, which resulted in the dependence of drug release on the physicochemical characteristics of hydrogel such as swelling, polymer erosion, and surface morphology. According to the results, the hydrogel containing 0.5% TEGDA which was prepared by freeze-drying method exhibited a porous structure with a high swelling ratio and displayed a sustained and complete drug release. It could be concluded that the hydrogel developed by this facile method is a good candidate with a potential for use in gastroretentive drug delivery systems.

Conducting hydrogels based on semi‐interpenetrating networks of polyaniline in poly(acrylamide‐co‐itaconic acid) matrix: synthesis and characterization

In this work, acrylamide/itaconic acid copolymeric hydrogels are prepared by free radical polymerization initiated by redox initiators of potassium persulfate and N,N,N′,N′‐tetramethyl ethylene diamine; N,N′methylene bisacrylamide was employed as a crosslinking agent. Aniline monomer was absorbed in the network of poly(acrylamide‐co‐itaconic acid) P(AAm‐co‐IA) hydrogel and followed by gamma radiation induced polymerization at room temperature. The novel semi‐interpenetrating network was comprised of linear polyaniline immersed in P(AAm‐co‐IA) matrix. Electrical conductivity of the hydrogels was measured using four‐probe technique. The conductivities for the prepared hydrogels are found to increase from 5.5 × 10−7 S cm−1 for P(AAm‐co‐IA) alone to 4.4 × 10−3 S cm−1 for semi‐interpenetrating polymer network P(AAm‐co‐IA)/polyaniline. Thus, a new composite hydrogel with good conductive properties also displaying enhanced mechanical strength and pH sensitivity was prepared. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Photoinduced charge-transfer electronic excitation of tetracyanoethylene/tetramethylethylene complex in dichloromethane

Based on the previous work on nonequilibrium solvation model by the authors, Intermolecular charge-transfer electronic excitation of tetracyanoethylene (TCE)/tetramethylethylene (TME) π-stacked complex in dichloromethane (DCM) has been investigated. For weak interaction correction, dispersion corrected functional DFT-D3 is adopted for geometry optimization. In order to identify the excitation metric, dipole moment components of each Cartesian direction, atomic charge, charge separation and Δr index are analyzed for TCE/TME complex. Calculation shows that the calculated excitation energy is dependent on the functional choice, when conjuncted with suitable time-dependent density functional, the modified nonequilibrium expression gives satisfied results for intermolecular charge-transfer electronic excitation.

Negative activation energies for carbene additions to tetramethoxyethylene

Activation energies were determined for the additions of three arylhalocarbenes to tetramethoxyethylene (TMeOE) and tetramethylethylene (TME) in pentane and decane. For addition of 3,5-dinitrophenylchlorocarbene to TMeOE in decane, Ea=−10.4±0.7kcal/mol, the most negative activation energy yet encountered in a carbene–alkene addition reaction. Computational studies parallel and elucidate the experimental results.

Photoisomerization of Vibrationally Hot Tetramethylethylene Produced by Ultrafast Internal Conversion from the Excited State.

Isomerization of tetramethylethylene (TME) following ultrafast internal conversion was investigated using time-resolved photoelectron spectroscopy with vacuum-ultraviolet probe pulses. The difference photoelectron spectrum at τ = 15 ps was reasonably well reproduced using a linear combination of static photoelectron spectra of TME and its isomers. The isomers were produced as a consequence of unimolecular reaction of vibrationally hot TME, created by internal conversion from the excited state.

Pressure-Dependent Criegee Intermediate Stabilization from Alkene Ozonolysis.

We explored the pressure dependence of acetone oxide (stabilized Criegee Intermediate, sCI) formation from 2,3-dimethyl-2-butene ozonolysis between 50 and 900 Torr using a new, highly accurate technique. We exploited the ability of the sCI to oxidize SO2 to H2SO4, which we measured with a chemical ionization mass spectrometer. We produced the Criegee intermediates (CI) in a high-pressure flow reactor via ozonolysis of 2,3-dimethyl-2-butene (tetramethyl ethylene, TME) and measured the relative H2SO4 concentrations with and without an added OH scavenger. Because the TME reaction with ozone forms acetone oxide (a syn-CI) with unit efficiency, we directly calculated the sCI yields at different pressures from the precisely measured ratio of the uncalibrated H2SO4 signal with and without the scavenger. We observed a linear pressure dependence between 50 and 900 Torr with a minimum stabilization of 12.7 ± 0.6% at 50 Torr and a maximum stabilization of 42 ± 2% at 900 Torr. A linear fit to the measured data points shows a zero-pressure intercept of 15 ± 2%, constraining the fraction of CI formed below the barrier for acetone oxide isomerization.

Unimolecular Decomposition Rate of the Criegee Intermediate (CH3)2COO Measured Directly with UV Absorption Spectroscopy.

The unimolecular decomposition of (CH3)2COO and (CD3)2COO was measured by direct detection of the Criegee intermediate at temperatures from 283 to 323 K using time-resolved UV absorption spectroscopy. The unimolecular rate coefficient kd for (CH3)2COO shows a strong temperature dependence, increasing from 269 ± 82 s(-1) at 283 K to 916 ± 56 s(-1) at 323 K with an Arrhenius activation energy of ∼6 kcal mol(-1). The bimolecular rate coefficient for the reaction of (CH3)2COO with SO2, kSO2, was also determined in the temperature range 283 to 303 K. Our temperature-dependent values for kd and kSO2 are consistent with previously reported relative rate coefficients kd/kSO2 of (CH3)2COO formed from ozonolysis of tetramethyl ethylene. Quantum chemical calculations of kd for (CH3)2COO are consistent with the experiment, and the combination of experiment and theory for (CD3)2COO indicates that tunneling plays a significant role in (CH3)2COO unimolecular decomposition. The fast rates of unimolecular decomposition for (CH3)2COO measured here, in light of the relatively slow rate for the reaction of (CH3)2COO with water previously reported, suggest that thermal decomposition may compete with the reactions with water and with SO2 for atmospheric removal of the dimethyl-substituted Criegee intermediate.

Photochemistry of oxygenated and deoxygenated solutions of the photosensitizer (2E,5E)-2,5-bis(4-dimethylaminobenzylidene)-cyclopentanone, a ketocyanine dye

Photochemical studies of (2E,5E)-2,5-bis(4-dimethylaminobenzylidene)-cyclopentanone (I) have been carried out. Compound I has been shown to sensitize the production of singlet oxygen (1O2) in deuterated toluene (C7D8), chloroform (CDCl3), and methanol (CD3OD). Tetramethylethylene (TME) was used as the indicator for 1O2 production. Photobleaching of solutions of the dye was observed, which led to an investigation of the chemical reactivity of I with 1O2. Based on 1H NMR, UV–Visible absorption spectroscopy, and HPLC/MS experimental data, it is proposed that the self-sensitized photooxidation of I with 1O2 yields 4-dimethylaminobenzaldehyde and (E)-3-(4-dimethylaminobenzylidene)-1,2-cyclopentadione as products. Photooxidation of I was not detected in CH3OH but was found in CD3OD. The absence of photooxidation in CH3OH is attributed to the short lifetime of singlet oxygen in this solvent (τΔ = 9.5 μs), compared to its lifetime in CD3OD (τΔ = 270 μs). UV–Visible absorption spectra of irradiated solutions of I in deoxygenated solvents demonstrate that (E,E) → (E,Z) photoisomerization of the dye takes place under these conditions.