Showing papers on "Aromatic hydrocarbon published in 2019"

Reversible, Room-Temperature C—C Bond Activation of Benzene by an Isolable Metal Complex

Abstract: The activation of C-C bonds is of fundamental interest in the construction of complex molecules from petrochemical feedstocks. In the case of the archetypal aromatic hydrocarbon benzene, C-C cleavage is thermodynamically disfavored, and is brought about only by transient highly reactive species generated in situ. Here we show that the oxidative addition of the C-C bond in benzene by an isolated metal complex is not only possible, but occurs at room temperature and reversibly at a single aluminium center in [(NON)Al]- (where NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene). Selectivity over C-H bond activation is achieved kinetically and allows for the generation of functionalized acyclic products from benzene.

Single-Step Conversion of H2-Deficient Syngas into High Yield of Tetramethylbenzene

Abstract: Controlling the selectivity in single-step conversion of syngas to single aromatic hydrocarbon to enhance CO utilization is a big challenge. By adapting the reaction coupling methodology, which allows the precise control of C–C coupling reaction, we obtained a high selectivity of ∼70% of a single product, tetramethylbenzene (TeMB), in hydrocarbons, at total CO conversion of 37%. This was enabled by the reaction of H2-deficient syngas over a composite catalyst of physically mixed nanosized ZnCr2O4 and H-ZSM-5. The H-ZSM-5 employed in this work appeared as a coffin shape with short straight channels [010] along the b-axis that exhibit low molecular-diffusion resistance, resulting in high selectivity of aromatics, particularly TeMB. Due to selective methanol formation and enhanced molecular diffusion, we observed an aromatic vacancy created inside H-ZSM-5 pores, which boosts the transformation of olefins into aromatics, thus making the aromatic cycle dominant in a dual-cycle mechanism and giving a high yield...

Aliphatic and aromatic hydrocarbons in comet 67P/Churyumov-Gerasimenko seen by ROSINA

Abstract: Context. Unlike all previous cometary space missions, the Rosetta spacecraft accompanied its target, comet 67P/Churyumov-Gerasimenko, for more than two years on its way around the Sun. Thereby, an unexpected diversity and complexity of the chemical composition was revealed.Aims. Our first step of decrypting the exact chemical composition of the gaseous phase is the identifying and quantifying the bulk composition of the pure aromatic and aliphatic hydrocarbons.Methods. For this study, data from ROSINA–Double Focusing Mass Spectrometer (DFMS) onboard the Rosetta spacecraft and the laboratory twin model were used. A joint campaign of laboratory calibration measurements and space data analysis was performed to derive the hydrocarbon bulk composition for the post-inbound equinox period at 1.52 AU in May 2015. Furthermore, several other mission phases were investigated to determine the dependencies of season, location, and heliocentric distance on the relative abundances of hydrocarbons.Results. It is shown that the bulk composition of the gaseous phase includes a high number of aliphatic compounds such as methane, ethane, and propane, as well as the aromatic compounds benzene and toluene. Butane and pentane were successfully identified in measurements at closer distance to the comet in May 2016. Furthermore, the presence of hexane and heptane in the coma is confirmed on rare occasions during the mission. Their presence in DFMS space data appears to be linked to days or periods of high dust activity. In addition to the saturated aliphatic and aromatic compounds, a high number of remaining unsaturated species is present, which cannot be explained by fragmentation of saturated species or contribution from other organic molecules in addition to pure hydrocarbons. This indicates the existence of unsaturated aliphatic and aromatic hydrocarbon molecules in the coma of comet 67P.

Carbon rings decorated with group 14 elements: New aromatic clusters containing planar tetracoordinate carbon

Abstract: A simple and chemically intuitive approach is used to design ptC-containing E–C clusters (E = Si–Pb). This approach consists in replacing three or two consecutive protons from an aromatic hydrocarbon by one E24+ or one E2+ fragment, respectively. In the model, electrons from E are removed from the pz orbitals, emptying them. Si–Pb favors the formation of a 3c-2e (E–C–E) σ-bond, which involves the ptC. Additionally, the π-electronic cloud is delocalized through the E-pz orbitals allowing the E atoms to effectively take part in the electronic delocalization, preserving the 4n + 2 Huckel's rule from the parent hydrocarbon. Two aromatic monocycles and one aromatic bicycle – benzene (C6H6), cyclopentadienyl anion (C5H5−) and pentalene dianion (C8H62−) – have been transformed into C–E systems. After an extensive exploration of their potential energy surfaces, four new global minima with ptC are identified, resulting from the substitution of the protons by Si and Ge cations in C5H5− and C8H62− (E3C5 and E4C8). The analysis of both the chemical bonding and the magnetic response to an external magnetic field confirms the aromatic character of these species.

Biostimulation potentials of corn steep liquor in enhanced hydrocarbon degradation in chronically polluted soil

Abstract: The effects of corn steep liquor (CSL) on hydrocarbon degradation and microbial community structure and function was evaluated in field-moist soil microcosms. Chronically polluted soil treated with CSL (AB4) and an untreated control (3S) was compared over a period of 6 weeks. Gas chromatographic fingerprints of residual hydrocarbons revealed removal of 95.95% and 94.60% aliphatic and aromatic hydrocarbon fractions in AB4 system with complete disappearance of nC1–nC8, nC10, nC15, nC20–nC23 aliphatics and aromatics such as naphthalene, acenaphthylene, fluorene, phenanthrene, pyrene, benzo(a)anthracene, and indeno(123-cd)pyrene in 42 days. In 3S system, there is removal of 61.27% and 66.58% aliphatic and aromatic fractions with complete disappearance of nC2 and nC21 aliphatics and naphthalene, acenaphthylene, fluorene, phenanthrene, pyrene, and benzo(a)anthracene aromatics in 42 days. Illumina shotgun sequencing of the DNA extracted from the two systems showed the preponderance of Actinobacteria (31.46%) and Proteobacteria (38.95%) phyla in 3S and AB4 with the dominance of Verticillium (22.88%) and Microbacterium (8.16%) in 3S, and Laceyella (24.23%), Methylosinus (8.93%) and Pedobacter (7.73%) in AB4. Functional characterization of the metagenomic reads revealed diverse metabolic potentials and adaptive traits of the microbial communities in the two systems to various environmental stressors. It also revealed the exclusive detection of catabolic enzymes in AB4 system belonging to the aldehyde dehydrogenase superfamily. The results obtained in this study showed that CSL is a potential resource for bioremediation of hydrocarbon-polluted soils.

On the relations between aromaticity and substituent effect

Abstract: Aromaticity/aromatic and substituent/substituent effects belong to the most commonly used terms in organic chemistry and related fields. The quantitative description of aromaticity is based on energetic, geometric (e.g., HOMA), magnetic (e.g., NICS) and reactivity criteria, as well as the properties of the electronic structure (e.g., FLU). The substituent effect can be described using either traditional Hammett-type substituent constants or characteristics based on quantum-chemistry. For this purpose, the energies of properly designed homodesmotic reactions and electron density distribution are used. In the first case, a descriptor named SESE (energy stabilizing the substituent effect) is obtained, while in the second case cSAR (charge of the substituent active region), which is the sum of the charge of the ipso carbon atom and the charge of the substituent. The use of the above-mentioned characteristics of aromaticity and the substituent effect allows revealing the relationship between them for mono-, di-, and polysubstituted π-electron systems, including substituted heterocyclic rings as well as quasi-aromatic ones. It has been shown that the less aromatic the system, the stronger the substituent influence on its π-electron structure. In all cases, when the substituent changes number of π-electrons in the ring in the direction of 4N+2, its aromaticity increases. Intramolecular charge transfer (a resonance effect) is privileged in cases where the number of bonds between the electron-attracting and electron-donating atoms is even. Quasi-aromatic rings, when attached to a truly aromatic hydrocarbon, simulate well the “original” aromatic rings, alike the benzene. For larger systems, a long-distance substituent effect has been found.

Hierarchical H-ZSM5 zeolites based on natural kaolinite as a high-performance catalyst for methanol to aromatic hydrocarbons conversion

Abstract: The present work introduces a good prospect for the development of hierarchical catalysts with excellent catalytic performance in the methanol to aromatic hydrocarbons conversion (MTA) process. Hierarchical H-ZSM5 zeolites, with a tailored pore size and different Si/Al ratios, were synthesized directly using natural kaolin clay as a low-cost silica and aluminium resource. Further explored for the direct synthesis of hierarchical HZSM-5 structures was the steam assisted conversion (SAC) with a cost-effective and green affordable saccharide source of high fructose corn syrup (HFCS), as a secondary mesopore agent. The fabricated zeolites exhibiting good crystallinity, 2D and 3D nanostructures, high specific surface area, tailored pore size, and tunable acidity. Finally, the catalyst performance in the conversion of methanol to aromatic hydrocarbons was tested in a fixed bed reactor. The synthesized H-ZSM5 catalysts exhibited superior methanol conversion (over 100 h up to 90%) and selectivity (over 85%) in the methanol conversion to aromatic hydrocarbon products.

Cave Drip Water-Related Samples as a Natural Environment for Aromatic Hydrocarbon-Degrading Bacteria.

Abstract: Restricted contact with the external environment has allowed the development of microbial communities adapted to the oligotrophy of caves. However, nutrients can be transported to caves by drip water and affect the microbial communities inside the cave. To evaluate the influence of aromatic compounds carried by drip water on the microbial community, two limestone caves were selected in Brazil. Drip-water-saturated and unsaturated sediment, and dripping water itself, were collected from each cave and bacterial 16S rDNA amplicon sequencing and denaturing gradient gel electrophoresis (DGGE) of naphthalene dioxygenase (ndo) genes were performed. Energy-dispersive X-ray spectroscopy (EDX) and atomic absorption spectroscopy (AAS) were performed to evaluate inorganic nutrients, and GC was performed to estimate aromatic compounds in the samples. The high frequency of Sphingomonadaceae in drip water samples indicates the presence of aromatic hydrocarbon-degrading bacteria. This finding was consistent with the detection of naphthalene and acenaphthene and the presence of ndo genes in drip-water-related samples. The aromatic compounds, aromatic hydrocarbon-degrading bacteria and 16S rDNA sequencing indicate that aromatic compounds may be one of the sources of energy and carbon to the system and the drip-water-associated bacterial community contains several potentially aromatic hydrocarbon-degrading bacteria. To the best of our knowledge, this is the first work to present compelling evidence for the presence of aromatic hydrocarbon-degrading bacteria in cave drip water.

Enhanced Ni-Al-Based Catalysts and Influence of Aromatic Hydrocarbon for Autothermal Reforming of Diesel Surrogate Fuel

Abstract: Aromatic hydrocarbons along with sulfur compounds in diesel fuel pose a significant threat to catalytic performances, due mainly to carbon deposition on the catalytic surface. In order to investigate the influence of an aromatic hydrocarbon on the autothermal reforming of diesel fuel, 1-methylnaphthalene (C11H10) was selected as an aromatic hydrocarbon. Two types of diesel surrogate fuel, i.e., DH (dodecane (C12H26) and hexadecane (C16H34) mixture) as well as DHM (DH fuel and C11H10 mixture) fuel, were prepared. A Rh-Al-based catalyst (R5A-I) was prepared using a conventional impregnation method. Various Ni-Al-based catalysts with Fe and Rh promoters were prepared via a polymer modified incipient method to improve the carbon coking resistance. These catalysts were tested under conditions of S/C = 1.17, O2/C = 0.24, 750 °C, and GHSV = 12,000 h-1 at DH or DHM fuel. R5A-I exhibited excellent catalytic performance in both DH and DHM fuels. However, carbon coking and sulfur poisoning resistance were observed in our previous study for the Ni-Al-based catalyst with the Fe promoter, which became deactivated with increasing reaction time at the DHM fuel. In the case of the Rh promoter addition to the Ni-Al-based catalysts, the catalytic performances decreased relatively slowly with increasing (from 1 wt.% (R1N50A) to 2 wt.% (R2N50A)) content of Rh2O3 at DHM fuel. The catalysts were analyzed via scanning electron microscopy combined with energy dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscopy. Gas chromatography-mass spectrometry detected various types of hydrocarbons, e.g., ethylene (C2H4), with catalyst deactivation. The results revealed that, among the produced hydrocarbons, C2H4 played a major role in accelerating carbon deposition that blocks the reforming reaction. Therefore, Rh metal deserves consideration as a carbon coking inhibitor that prevents the negative effects of the C2H4 for autothermal reforming of diesel fuel in the presence of aromatic hydrocarbons.

Supramolecular steric hindrance effect on morphologies and photophysical behaviors of spirocyclic aromatic hydrocarbon nanocrystals

Abstract: Three pyrene-based spirocyclic aromatic hydrocarbons (Py-SAHs) were prepared to clarify the roles of molecular segments in regulating the morphologies and photophysical properties of organic microcrystals. Due to the different supramolecular steric hindrance (SSH) effect between bulky groups and pyrene rings, distinct nanocrystal morphologies with unique photoluminescence properties were realized.

Catalytic Pyrolysis of Hemicellulose to Produce Aromatic Hydrocarbons

Abstract: Catalytic fast pyrolysis of hemicellulose with zeolite catalysts is a promising method to produce aromatic hydrocarbons (Carlson et al. 2009). In this paper, the behavior of hemicellulose catalytic pyrolysis with HZSM-5 (with three different silica to alumina ratio, 23, 50, 80), HY, and Hβ was studied. Pyrolysis vapor was separated into non-condensable vapors and condensable fractions. The fractions were qualified and quantified by a gas chromatography / flame ionization detector (GC/FID) system and a gas chromatography / mass spectrometer (GC/MS) system, respectively. The influences of catalysts and pyrolysis parameters were studied. Among the catalysts, HZSM-5(23) provided the desired acidity and shape selectivity for aromatic hydrocarbon production. A higher catalyst to hemicellulose ratio (CHR) and higher heating rate resulted in a higher aromatic hydrocarbon yield. The most suitable pyrolysis temperature for hemicellulose with HZSM-5 was 650 °C. During catalytic pyrolysis, thermal decomposition products underwent deoxygenation reactions promoted by the acid sites on the zeolite. The C2-C4 deoxygenated products produced monocyclic aromatic hydrocarbons (MAH) by shape-selective catalysis reactions in zeolite pores. With higher temperatures and higher residence times, monocyclic aromatic hydrocarbons facilitated cyclization reactions with C2-C4 deoxygenated products, thereby forming polycyclic aromatic hydrocarbons (PAH).

Quantitation of benzene in flavourings and liquid foods containing added cherry-type flavour by a careful work-up procedure followed by a stable isotope dilution assay

Abstract: The exposure of humans to the aromatic hydrocarbon benzene should be minimized due to its carcinogenicity. Previous studies have reported on the presence of benzene, in particular in foods with added cherry aroma compounds, in particular benzaldehyde. To allow a reliable quantitation of benzene, a stable isotope dilution assay using (2H3)benzene as the internal standard was developed and solid phase microextraction (SPME) was used for volatile isolation followed by GC × GC–TOFMS analysis. Care was taken to avoid any exposure to light and to use materials during work-up, which were free of benzene contamination. The method, applied on 22 liquid foods with added flavour showed that benzene did not exceed a concentration of 1 µg/L in any sample (i.e. the limit established for drinking water). Furthermore, flavourings containing benzaldehyde and the corresponding raw material were analysed. The major source of benzene in flavourings turned out to be benzaldehyde itself. First insights into parameters supporting the formation pathway of benzene from benzaldehyde were obtained indicating that the presence of light and either acidic or alkaline conditions favoured benzene formation.

Anthracene-Attached Persistent Tricyclic Aromatic Hydrocarbon Radicals.

Abstract: Anthracene-attached tricyclic aromatic hydrocarbon radicals having different central polygons, Ant-5, Ant-6, and Ant-7, were synthesized to evaluate the role of an anthracene substituent group in the stability and reactivity of tricyclic aromatic hydrocarbon radicals. The bulky anthryl group effectively protects a carbon atom with high spin density, resulting in high persistence of the radicals. On the other hand, the combination of the anthryl group and the tricyclic aromatic scaffold makes the molecular structure drastically change from a twisted form to a folded form and an unpaired electron moves into the anthryl moiety, eventually affording a tail-to-tail σ-dimer.

Molecular recognition of planar and non-planar aromatic hydrocarbons through multipoint Ag-π bonding in a dinuclear metallo-macrocycle

Abstract: Exploration of a novel structural motif of host–guest interactions is one of the most fundamental topics to develop macrocycle-based host–guest/supramolecular systems. Herein, we present an unprecedented mode of inclusion of aromatic hydrocarbons into a macrocyclic cavity via multipoint Ag–π bonding as a driving force. A dinuclear AgI-macrocycle encapsulated one molecule of anthracene, a typical planar aromatic hydrocarbon, in solution and in the solid state. Single-crystal X-ray diffraction analysis of the host–guest inclusion complex revealed the binding of anthracene via multipoint Ag–π bonding to both AgI ions arranged within the open-ended nano-cavity of the dinuclear AgI-macrocycle. Notably, this binding motif based on Ag–π bonding was also applied to the inclusion of triptycene, a non-planar aromatic hydrocarbon with a steric tripodal structure, to evaluate the rotational motion of the molecular paddle-wheel in the AgI-macrocycle.

Ascertaining the factors that influence the vapor sensor response: The entire case of MWCNT network sensor

Abstract: This paper endeavors to answer an important question posed during the fabrication of vapor sensors based on multiwall carbon nanotubes (MWCNTs): How do the preparation and measurement conditions influence the sensor response in real-life situations? A satisfactory answer could be given in view of the effects produced by the surface functionalization of MWCNTs and various solvent vapors. To this end, this case study was designed upon modified-MWCNT-networks (Ns) with alkyl diol (EG) and alkyl diamine (EDA, HDA) treatments, and the sensor responses of these networks were examined in respect of the following vapors: water and different solvents from the groups of paraffinic hydrocarbon, aromatic hydrocarbon, halohydrocarbon, ether, ketone, aldehyde, ester, and nitrogen containing compounds, sulphur containing compounds, alcohols and acids. In addition, an applied sensor based on MWCNT (HDA)-N was evaluated by measuring various alcoholic beverages and vinegar.

Efficient catalytic oxidation of methyl aromatic hydrocarbon with N-alkyl pyridinium salts

Abstract: A series of N-alkyl pyridinium salts were synthesized and employed as metal-free catalyst for the selective oxidation of methyl aromatic hydrocarbon with molecular oxygen. The electronic effect of the substitutes was found to be an important factor for the catalytic performance. With the introduction of electron-donating substitute –N(CH3)2, the conversion of p-xylene and selectivity of p-toluic acid could be simultaneously increased. 1-Benzyl-4-N,N-dimethylaminopyridinium salt showed the highest catalytic activity, and 95% conversion with 84% of selectivity to p-toluic acid could be obtained for the selective oxidation of p-xylene. Several methyl aromatic hydrocarbons could all be efficiently oxidized with the reported catalyst at the absence of any metal species.

Polyaromatic molecule having a nitrile oxide function

Abstract: The invention relates to a compound of the following formula (I): (I) wherein: - PAr is a polyaromatic group comprising at least two condensed aromatic hydrocarbon rings, each of said condensed aromatic rings optionally being substituted by one or more carbon chains which are identical or different, aliphatic or aromatic, linear, branched or cyclic, optionally substituted or interrupted by one or more heteroatoms; and - Sp is an atom or a group of atoms.