Alkyl-substituted Aromatic Compounds Research Articles

Ring-Cleavage Products Produced during the Initial Phase of Oxidative Treatment of Alkyl-Substituted Aromatic Compounds.

Chemical oxidation with hydroxyl radical (HO•) and sulfate radical (SO4•-) is often used to treat water contaminated with aromatic compounds. Although oxidation of aromatics by these radicals has been studied for decades, the commonly accepted transformation pathway-sequential hydroxylation of the ring followed by ring cleavage and mineralization of the resulting products-does not account for the loss of the parent compound observed during the initial phase of the process. To assess the importance of pathways for aromatic compound oxidation that do not result in ring hydroxylation, we identified products formed after the initial reaction between HO• or SO4•- and benzene, toluene, ethylbenzene, and (BTEX) xylene isomers. We quantified products of ring hydroxylation and oxidation of alkyl substituents as well as a suite of ring-cleavage products, including acetaldehyde, formic acid, 6-, 7-, or 8-carbon oxoenals and oxodials. Other ring-cleavage products, which were most likely aldehydes and organic acids, were observed but not quantified. When SO4•- was used as the oxidant, aromatic organosulfates also were formed. Our results indicated that the initial phase of the oxidation process involves radical addition, hydrogen abstraction, or one-electron transfer to the ring followed by reaction with O2. The hydroxycyclohexadienylperoxy radical produced in this reaction can eliminate hydroperoxyl radical (HO2•) to produce a phenolic compound or it can rearrange to form a bicyclic peroxy intermediate that subsequently undergoes ring cleavage. Hydroxylation of the ring and oxidation of the alkyl substituent accounted for approximately 15-40% of the reacted mass of the parent compound. Ring-cleavage products for which quantification was possible accounted for approximately 2 to 10% of the reacted mass. Our results raise concerns about the formation of toxic ring-cleavage products during the initial stage of oxidation whenever HO• or SO4•- is used for the treatment of water containing benzene or alkylbenzenes.

Identification of the genetic heterogeneity of Tatarstan oils based on the composition of alkyl-substituted aromatic compounds

This study presents data on concentrations of n-alkylbenzenes, n-alkylnaphthalenes, phytanylnaphthalene, and methylphytanylnaphthalene in representative crude oils of Tatarstan. The results of the study reveal the elevated concentrations of C19, C21, and C23 homologues of n-alkylbenzenes and n-alkylnaphthalenes, which can be considered as biomarkers. The proposed procedure for comprehensive quantification of this group of biomarkers can be used as an efficient tool to study oils from the major petroleum basins of Russia. Based on the results of the study, four genetic groups of oils in Tatarstan have been distinguished: (1) oils from the north and northwest (Bir saddle, Lower Kama system of linear faults, and Saraily saddle), (2) oils from Devonian terrigenous reservoirs within the South Tatar arch and Melekes depression, (3) oils from Carboniferous reservoirs, and (4) oils from Devonian carbonate reservoirs. All these oils belong to the same genetic macrotype. Based on the results of this study, the sedimentary sections of the Melekes depression cannot be regarded as potential source rocks. It is assumed that oil has migrated to the northern part of the region from the north or east. Some of the possible migration routes for oils from the remaining part of Tatarstan are from the southeast and/or south.

Efficient upgrading process for production of low quality fuel from bio-oil

To improve the quality of fast pyrolysis bio-oil, an efficient catalytic upgrading process is proposed with pristine Ni/MgO catalyst and ethanol. Esterification, hydrogenation, alkylation of aromatic ring and depolymerization of lignin-derived pyrolytic oligomers simultaneously occurred in the upgrading process. Esters, ketones and alkyl-substituted aromatic compounds were found to be the main components in the volatile fraction of the upgraded bio-oil. Under the optimal conditions, pH value and HHV (high heating value) of the upgraded bio-oil were 5.01 and 24.9MJkg−1, respectively. This result suggested that the properties of bio-oil could be effectively improved by the catalytic upgrading process. Moreover, carbon efficiency of this upgrading process was relatively high because that formation of coke is suppressed in the upgrading process.

Electrocatalytic Hydrocarbon Hydroxylation by Ethylbenzene Dehydrogenase from Aromatoleum aromaticum

We report the electrocatalytic activity of ethylbenzene dehydrogenase (EBDH) from the β-proteobacterium Aromatoleum aromaticum. EBDH is a complex 155 kDa heterotrimeric molybdenum/iron-sulfur/heme protein which catalyzes the enantioselective hydroxylation of nonactivated ethylbenzene to (S)-1-phenylethanol without molecular oxygen as cosubstrate. Furthermore, it oxidizes a wide range of other alkyl-substituted aromatic and heterocyclic compounds to their secondary alcohols. Hydroxymethylferrocenium (FM) is used as an artificial electron acceptor for EBDH in an electrochemically driven catalytic system. Electrocatalytic activity of EBDH is demonstrated with both its native substrate ethylbenzene and the related substrate p-ethylphenol. The catalytic system has been modeled by electrochemical simulation across a range of sweep rates and concentrations of each substrate, which provides new insights into the kinetics of the EBDH catalytic mechanism.

Bimetallic Palladium-Platinum-on-Carbon-Catalyzed H-D Exchange Reaction: Synergistic Effect on Multiple Deuterium Incorporation

We prepared several activated carbon-supported bimetallic Pd-Pt catalysts (Pd-Pt/C) by using various reducing reagents, and examined their catalytic activities for the deuteration of alkyl-substituted aromatic compounds. Multiple deuterations catalyzed by Pt-Pd/C proceeded in D 2 O at 180 °C under a H 2 atmosphere, and a synergistic effect was observed in relation to the incorporation of deuterium at sterically hindered positions on aromatic rings.

H-D Exchange Reaction Taking Advantage of the Synergistic Effect of Heterogeneous Palladium and Platinum Mixed Catalyst

An effective and applicable deuteration method for alkyl-substituted aromatic compounds using a heterogeneous Pd/C and Pt/C mixed catalyst in deuterium oxide in the presence of a small amount of hydrogen gas was developed. Mixing a heterogeneous palladium and platinum catalyst provides an interesting synergistic effect in the H-D exchange reaction and leads to full H-D exchange results even on sterically hindered sites, which indicated only low-deuterium efficiencies when either Pd/C or Pt/C were used independently as a catalyst. We investigated the synergistic effect using a variety of substrates and proved the broad generality of the heterogeneous Pd-Pt-D2O-H2 system in the H-D exchange reaction. Furthermore, this system could be applied to a multigram scale synthesis of useful deuterium-labeled compounds, such as deuterium-labeled bis-aniline derivatives as raw materials for polyimides, aryl iodides as synthetic building blocks, and biologically active compounds.

Toluene Combustion: Reaction Paths, Thermochemical Properties, and Kinetic Analysis for the Methylphenyl Radical + O2 Reaction

Aromatic compounds such as toluene and xylene are major components of many fuels. Accurate kinetic mechanisms for the combustion of toluene are, however, incomplete, as they do not accurately model experimental results such as strain rates and ignition times and consistently underpredict conversion. Current kinetic mechanisms for toluene combustion neglect the reactions of the methylphenyl radicals, and we believe that this is responsible, in part, for the shortcomings of these models. We also demonstrate how methylphenyl radical formation is important in the combustion and pyrolysis of other alkyl-substituted aromatic compounds such as xylene and trimethylbenzene. We have studied the oxidation reactions of the methylphenyl radicals with O2 using computational ab initio and density functional theory methods. A detailed reaction submechanism is presented for the 2-methylphenyl radical + O2 system, with 16 intermediates and products. For each species, enthalpies of formation are calculated using the computational methods G3 and G3B3, with isodesmic work reactions used to minimize computational errors. Transition states are calculated at the G3B3 level, yielding high-pressure limit elementary rate constants as a function of temperature. For the barrierless methylphenyl + O2 and methylphenoxy + O association reactions, rate constants are determined from variational transition state theory. Multichannel, multifrequency quantum Rice-Ramsperger-Kassel (qRRK) theory, with master equation analysis for falloff, provides rate constants as a function of temperature and pressure from 800 to 2400 K and 1 x 10(-4) to 1 x 10(3) atm. Analysis of our results shows that the dominant pathways for reaction of the three isomeric methylphenyl radicals is formation of methyloxepinoxy radicals and subsequent ring opening to methyl-dioxo-hexadienyl radicals. The next most important reaction pathway involves formation of methylphenoxy radicals + O in a chain branching process. At lower temperatures, the formation of stabilized methylphenylperoxy radicals becomes significant. A further important reaction channel is available only to the 2-methylphenyl isomer, where 6-methylene-2,4-cyclohexadiene-1-one (ortho-quinone methide, o-QM) is produced via an intramolecular hydrogen transfer from the methyl group to the peroxy radical in 2-methylphenylperoxy, with subsequent loss of OH. The decomposition of o-QM to benzene + CO reveals a potentially important new pathway for the conversion of toluene to benzene during combustion. A number of the important products of toluene combustion proposed in this study are known to be precursors of polyaromatic hydrocarbons that are involved in soot formation. Reactions leading to the important unsaturated oxygenated intermediates identified in this study, and the further reactions of these intermediates, are not included in current aromatic oxidation mechanisms.

Oxidation of Alkyl‐Substituted Aromatic Compounds with Air

AbstractFor Abstract see ChemInform Abstract in Full Text.

Small-scale hydrous pyrolysis of macromolecular material in meteorites

The hydrous pyrolysis method, usually performed on several hundred grams of terrestrial rock sample, has been scaled down to accommodate less than two grams of meteorite sample. This technique makes full use of the high yields associated with hydrous pyrolysis experiments and permits the investigation of the meteorite macromolecular material, the major organic component in carbonaceous meteorites. The hydrous pyrolysis procedure transforms the high molecular weight macromolecular material into low molecular weight fragments. The released entities can then be extracted with supercritical fluid extraction. In contrast to the parent structure, the pyrolysis products are amenable for analysis by gas chromatography-based techniques. When subjected to hydrous pyrolysis, two carbonaceous chondrites (Orgueil and Cold Bokkeveld) released generally similar products, which consisted of abundant volatile aromatic and alkyl-substituted aromatic compounds. These results revealed the ability of small-scale hydrous pyrolysis to dissect extraterrestrial macromolecular material and thereby reveal its organic constitution.

Characterization of Asphaltenes Molecular Structure

The features of molecular structure of seven n-C7 asphaltenes isolated from different feedstocks (i.e., vacuum residue, atmospheric residue and crude oil) have been investigated by pyrolysis−gas chromatography/mass spectrometry (Py-GC/MS), and their average structural parameters have been estimated using a mathematical optimization method. The results of structural analysis pointed out substantial differences among the asphaltenes investigated. The size of aromatic fused ring systems ranged from 5.1 to 14.9, while a substantial fraction of peripheral carbon in hydroaromatic/aromatic sheets (0.28−0.40) is substituted with aliphatic chains whose average length was between 2.8 and 6.3. A significant fraction of aliphatic moiety (0.15−0.48) was found to be present as naphthenic structures. In all cases, the main classes of compounds identified during pyrolysis tests were homologous series of alkanes (up to C25-30), 1-alkenes (up to C25-30), branched paraffins, and alkyl-substituted aromatic compounds. The formation of pyrolysis products was explained on the basis of literature data regarding thermolysis reactions of model compounds mimicking the structural features of asphaltenes. The results of this study are consistent with the view that asphaltenes are a complex polydisperse mixture of molecules made up of polyaromatic and hydroaromatic units joined by aliphatic bridges and substituted with aliphatic chains containing up to 25−30 carbon atoms. However, both NMR data and results of structural analysis indicate that the major part of these chains (more than 80%) is formed by short alkyl groups (C1−C4).

Thermal decomposition behaviour and structural characteristics of asphaltenes

The thermal behavior of 7 characterized n-C7 asphaltenes has been investigated by thermogravimetry and pyrolysis/gas chromatography/mass spectrometry (Py/GC/MS). Analytical data and results of structural analysis reveal substantial differences among the n-C7 asphaltene samples. The aromatic carbon fraction ranged between 0.69 and 0.48 and the sulphur content was between 2.9 and 10.8%. A substantial fraction of peripheral carbon in hydroaromatic/aromatic sheets (0.2 – 0.3) was substituted with aliphatic chains and a significant fraction of the aliphatic moieties (15–48%) were found to be present as naphthenic structures. Results of TG pyrolysis and 13CNMR data showed that final yields of pyrolysis depended linearly on the aliphatic carbon fraction of the asphaltene. A linear relationship was also found between the fraction of sulphur evolved and final weight losses. Analysis of volatile matter by FT-ir and the Py/GC/MS technique indicated that its composition was predominantly aliphatic (∼ 80%) while the remainder was formed by alkyl-substituted aromatic compounds. The main classes of compounds identified were n-alkanes, l- n alkanes, isoalkanes, cycloalkane and alkyl-substituted benzene. The amount of methane formed during pyrolysis ranged between 5.8 and 8.7% of carbon present in the initial sample. Its formation occurs mainly at high degrees of conversion, apparently through two reaction pathways. A non isothermal technique using different heating rates was applied to determine the kinetic parameters of asphaltene pyrolysis. In each case, the data showed an increase of Eact during reaction, particularly at high conversion degrees.

Comparison of several contemporary ionization/mass analyzer techniques for large components of complex fossil-derived materials

Coals and coal-derived samples provide a unique mixture for development and comparison of mass spectrometric techniques for high molecular weight analyses. The Argonne Premium Coal samples (APCS) are convenient for assessing classical and novel mass spectrometric techniques. Vacuum pyrolysis mass spectrometry of APCS 4 (Pittsburgh No. 8) has been reported. Alkyl-substituted aromatic compounds and hydroxy- and dihydroxy-substituted aromatic compounds were observed. Newer techniques such as laser desorption (LD), as well as in-beam techniques, such as desorption chemical ionization (DCI) and desorption electron ionization (DEI) are better suited to the studies of mixture characterization as presented by fossil fuels.

Investigation of subbituminous coals by thermogravimetry-mass spectrometry: Part 1. formation of hydrocarbon products

The thermal decomposition of a series of subbituminous coals from a Hungarian coal basin was investigated by thermogravimetry-mass spectrometry at a heating rate of 20°C min −1. The mass spectrometric intensities of the aliphatic products (C n H m , n ⩾ 2) and alkyl-substituted aromatic compounds evidenced similar sharp peaks at about 490°C. Methane evolved at higher temperatures in a broader temperature range. Benzene curves were composed of two overlapping peaks and were resolved by least-squares reaction kinetic calculations. The low and high temperature peaks of the benzene curves were near to the peaks of the aliphatic C n H m ( n⩽2) compounds and methane respectively. The amounts of the various products were estimated by the integral of the corresponding mass spectrometric intensities and were correlated with coal rank. The probable sources of the various product compounds were discussed.

Simulation of carbon-13 nuclear magnetic resonance spectra of alkyl-substituted aromatic compounds

Carbon-13 nuclear magnetic resonance spectra for a collection of alkyl-substituted benzenes and polycyclic aromatic compounds have been simulated by using computer-based methodology. Several new types of structure-based parameters were developed and were shown to be useful in characterizing structural features related to the conjugated {pi} systems present in these molecules. These new descriptors, along with others developed previously, were used to generate parametric equations for chemical shift prediction using a training set of 30 compounds. Two different approaches for the grouping of aromatic ring carbons were investigated and evaluated for use in generating accurate chemical shift models and complete simulated spectra. Partial simulated spectra were also constructed, such that the methyl carbon atom resonances were excluded, to assist in the evaluation of the ring carbon atom model equations. The external predictive ability of the derived models was evaluated through the simulation of {sup 13}C NMR spectra for a group of 44 compounds not included in the model development process. External prediction accuracy improved when ring-bridging and non-ring-bridging carbons were treated separately.

Structural Effects on Selective Aliphatic Hydrogen Exchange in Alkyl-Substituted Aromatic Compounds in Deuteriated Trifluoroacetic Acid.

Structural Effects on Selective Aliphatic Hydrogen Exchange in Alkyl-Substituted Aromatic Compounds in Deuteriated Trifluoroacetic Acid.

Isolation and characterization of spontaneously occurring TOL plasmid mutants of Pseudomonas putida HS1.

A strain of Pseudomonas (P. putida HS1) was found to resemble P. putida (arvilla) mt-2 in its ability to degrade toluene, m- and p-xylene, 1,2,4-trimethylbenzene (pseudocumene), and 3-ethyltoluene via oxidation of a methyl substituent and reactions of the meta-fission pathway. The ability to degrade these substrates by P. putida HS1 (PpC1) was shown to be encoded by a TOL (pDK1) plasmid as evidenced by: (i) spontaneous loss of the TOL-related phenotype after growth with benzoate, (ii) transfer of the TOL character from the wild type into cured recipients by conjugation, and (iii) isolation of a plasmid of identical molecular weight (120 X 10(6)) from both the wild type and an exconjugant obtained by mating wild type with a putative cured recipient. In addition to the isolation of apparent cured strains having lost the entire TOL-related phenotype, two additional mutant classes were observed after growth on benzoate. One class, represented by PpCT1, was unable to utilize the alkyl-substituted aromatic compounds but retained the ability to grow with toluene and benzyl alcohol. Analysis of PpCT1 revealed that it was unable to synthesize the TOL-encoded toluate oxidase and enzymes of the meta pathway but retained the ability to elaborate activities for toluene hydroxylase, benzyl alcohol, and benzaldehyde dehydrogenase, thereby mediating initial oxidation of toluene to benzoate, which was then further metabolized via enzymes of the chromosomally encoded ortho-fission pathway. A second class of mutants had lost the ability to utilize the hydrocarbons but could still grow with m-toluate but not p-toluate, 3,4-dimethylbenzoate, or 3-ethylbenzoate, intermediates in the oxidation of the corresponding hydrocarbons. Our such mutant, PpCM1, could no longer synthesize enzymes required for initial oxidation of the hydrocarbons, but was able to produce the toluate oxidase and enzymes of the meta pathway, thereby facilitating degradation of m-toluate. Neither PpCT1, PpCM1, nor a putative cured strain, PpCC1, reverted at detectable frequencies (less than 10(-9). Analysis of each strain for plasmid deoxyribonucleic acid revealed the presence of a single plasmid in each strain with the following molecular weights: PpCM1, 100 X 10(6) (pDKM1); PpCT1, 80 X 10(6) (pDKT1); PpCC1 20 X 10(6) (pDKC1). The results suggest that the TOL (pDK1) plasmid has undergone deletions giving rise to smaller replicons which either encode for only a fraction of the wild-type catabolic functions (pDKM1, pDKT1) or have lost all catabolic activities (pDKC1).

Kettenlängeneffekte in paraffinen—VI: Über die elektronische steuerung der nitrierung von hydrochinonmethylalkyldiäthern durch alkylketten von C 1–C 16

Mononitration of hydroquinone methylakyl (C 1–C 16) diethers in different solvents and wi t ̵ different nitrating agents leads to an isomer ratio of ortho and meta nitro compounds which depends on the length of the paraffin chain as well as branching and substitution in the chain. Kinetic measurements and evaluation of UV, IR, NMR as well as Mössbauer-spectra show that the course of the reaction is determined mainly by electronic effects in the paraffin chain. Therefore, these results support a recently described model (“Stäbchen-Modell”). In alkyl-substituted aromatic compounds if a distinction is made between an inductive ( m-activating) and a resonance effect ( o/p-activating) in the electrophilic aromatic substitution, the contradictory results of the Baker-Nathan effect can be explained.