Investigation of aromatic carbon sites in materials derived from petroleum and coal using 13C n.m.r. methods

Aromatic C and CH carbon sites in a variety of petroleum and coal derived materials have been investigated using a ¹³C n.m.r. technique termed spin echo broad band off-resonance decoupling (SEBBORD). Only resonances due to non-protonated aromatic carbon sites are observed in SEBBORD spectra such that comparison with conventional ¹³C n.m.r. spectra enables differentiation between aromatic C and CH group resonances. Relative abundances of non-protonated aromatic carbon sites calculated from SEBBORD data are in good agreement with values derived from a combination of conventional¹H n.m.r., ¹³C n.m.r. and elemental analysis data. The occurrence of significant proportions of aromatic C intensity to high field of 129–130 ppm and of aromatic CH intensity to low field of 129–130 ppm has been found to be quite common. Consequently attempts to determine aromatic C and CH group abundances by partitioning conventional ¹³C n.m.r. spectra in the vicinity of 129–130 ppm can lead to considerable quantitative errors. SEBBORD provides more detailed information about aromatic carbon sites than can be obtained from conventional ¹³C n.m.r. spectra.     

Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of Victorian brown coal. Part VII. Raman spectroscopic study on the changes in char structure during the catalytic gasification in air

FT-IR/Raman spectroscopies have been used to identify the structural features of Victorian brown coal chars during the gasification in air at 400 °C. The deconvolution of the Raman spectra has allowed us to identify the main structural sites in char where preferential reaction with O₂ takes place. The presence of Na and Ca catalysts is shown to alter the reaction pathways between char and O₂. In the absence of a catalyst, the O-containing functional groups formed in char during gasification were closely associated with the aromatic structure and thus tended to loosen the aromatic structure. The non-catalysed gasification was slow and took place on some specific (especially sp³-rich or sp²–sp³ mixture) sites distributed throughout the char. In the presence of a catalyst (Na or Ca), the O-containing functional groups were not closely associated with the main aromatic structure throughout the char. The catalytic gasification reactions were localised on the sites associated with the catalysts. The preferential removal of smaller aromatic ring systems and the persistence of cross-linking structures in the presence of a catalyst mean that the large aromatic ring systems were increasingly concentrated with little flexibility, affecting the dispersion of catalyst.     

Determination of aromatic hydrocarbon fraction in oil shale by 13C n.m.r. with magic-angle spinning

A method for estimation of aromatic content in oil shales is demonstrated. Magic-angle spinning at 2 kHz is shown to remove chemical shift anisotropy to a sufficient degree to resolve aromatic and aliphatic ¹³C n.m.r. spectral regions for a lithic oil shale specimen. The proton and carbon n.m.r. relaxation parameters are such as to allow room-temperature use of this proton-enhanced ¹³C n.m.r. technique as a quantitative analytical tool. Cross polarization times of a millisecond or less and experiment repetition periods of 0.5 s or less are optimum. The specimen examined is represented by an aromatic carbon fraction 0.264 ± 0.007; this determination is quite insensitive to the proton-carbon cross polarization time. Spectra for kerogen, shale oil, and dawsonite are also presented. Dawsonite may interfere in the determination of the aromatic fraction.     

The carbon nitride films prepared at various substrate temperatures by vacuum cathodic arc method

Carbon nitride films have been grown by vacuum cathodic arc method in the substrate temperature range of 100–500 °C. The bonding structure of the films was investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and infrared (IR) spectroscopy. With increasing substrate temperature, the films indicate various characteristics. At 100 °C, it can be described as a network similar to DLC in which aromatic sp²C phase is cross-linked by sp³C phase. Between 200 and 400 °C, with increasing substrate temperature the films become graphitized and the sp²CN phase increases, meanwhile the non-aromatic sp²CN phase appears at the edges of aromatic clusters in planar position as well as in out-of-planar regions. While at 500 °C the non-aromatic sp²CN phase almost comes to the same level as the aromatic sp²CN phase. So in the network of the film the aromatic sp²C phase is cross-linked by the non-aromatic sp²C phase. Based on the variation of the microstructure of the films, a comprehensive assignment pattern for the XPS C1s and N1s at different substrate temperature is proposed. In addition, the interpretation of p electron band in valence band spectra at various substrate temperatures is also discussed.     

Separation and spectroscopic analysis of the aromatic fraction of oils from lignite depolymerization

The aromatic fraction of oils obtained by catalytic depolymerization of a Spanish subbituminous coal has been separated by means of liquid chromatography on partially deactivated alumina into six subfractions, which were studied by i.r. and ¹H n.m.r. spectroscopy. The results indicate hydroaromatic structures with a low degree of condensation, with one to three aromatic nuclei on average, short chain alkyl substituents and significant amounts of -OH and aromatic ether groups.     

On the use of infrared spectroscopy in the study of carbon dioxide decomposition on copper containing methanol synthesis catalysts

A novel and convenient procedure for the catalytic acylation of a series of aromatic compounds such as benzene, toluene, xylenes (o-, m-, p-), mesitylene, isopropylbenzene and N,N-dimethylaniline to the corresponding ketones using medium- and large-pore zeolites as catalyst and acetic acid or acetyl chloride as acylating agent at different reaction temperatures in a tubular reactor is demonstrated for the first time. The H-ZSM5 and H-beta zeolite catalysts exhibited the higher turnover rates (TOF× 10^-3 s^-1 mol^-1 Al) for the acetic acid or acetyl chloride conversion to the products. In some cases, nearly total conversion of acylating agent with very high selectivity to the para product is achieved. It is found that the reactivity of the aromatic compounds increases with the increase of -CH₃ groups in the benzene ring. Mechanistically, it is assumed that an active species (CH₃CO⁺) is generated catalytically from the acylating agent by an acidic zeolite which attacks the aromatic ring and produces corresponding aromatic ketones.     

Specific Ortho-bromination. I. Preparation of ortho-bromo substituted benzenes

A process¹ for the synthesis of ortho-bromo aromatic compounds was studied. The process is based on the blocking and shielding effect of a tertiary butyl group which is introduced on to the aromatic ring prior to bromination. The removal of the tertiary butyl group, after bromination, is accomplished by transferring it to another aromatic nucleus via an aluminium trichloride catalysed transalkylation reaction. Synthesis of six different compounds are described and a recycle process is illustrated.     

1H n.m.r. study of tars from flash pyrolysis of three Australian coals

The structure and composition of tars from the flash pyrolysis of one brown and two bituminous Australian coals were investigated by ¹H n.m.r. spectroscopy. Reaction times in a fluidized bed were about 1 s. For each tar the aromatic hydrogen content increases slightly with pyrolysis temperature up to ≈650 °C and then rapidly up to 900 °C. The aromatic carbon content increases rectilinearly with temperature. The yield of aromatic carbon reaches a maximum at 600–700 °C, and then decreases; the yield of aromatic hydrogen is independent of temperature. The proportion of aromatic material with condensed ring structures increases with temperature. Three temperature zones of reactivity can be recognized. Polymethylene chains and aromatic groups are stable up to 600 °C. Between 600 and 700 °C aliphatic substituents, other than α groups, decompose; between 700 and 900 °C α-aliphatic and aromatic groups also decompose, resulting in lower yields of tar.     

Hydrogenolysis products of pyridine extract of a Japanese lignite

Petroleum ether insoluble fractions of a pyridine extract of a Japanese lignite were pyrolysed with tetralin. The chain length of alkyl groups bonded to aromatic rings and the average chemical structure of aromatic compounds in the lignite were obtained from analyses of hydrogenolysis products. Gas Chromatographic analyses of fractions eluted by cyclohexane showed the presence of C₁₅ to C₃₄ straight-chain alkanes. The chemical structures of the other fractions were analysed quantitatively by a combination of ¹³C and ¹H n.m.r. The unit structure of petroleum ether insoluble fractions in the lignite consists of one to three aromatic rings with straight-chain alkyl groups, some of which are about 25–30 carbon atoms long.     

Structural characterization of Saudi Arabian medium crude oil by n.m.r. spectroscopy

Saudi Arabian medium crude oil has been characterized by ¹H and ¹³C n.m.r. spectroscopy. Several structural parameters such as the percentage of aliphatic carbons, aromatic carbons, n-alkanes, naphthenes, branched alkanes and chain length of paraffinic chains were calculated. The aromatic carbons were further classified as those attached to a hydrogen, methyl or alkyl group, or bridgehead carbons.     

Sensing Cu2+ by controlling the aggregation properties of the fluorescent dye rhodamine 6G with the aid of polyelectrolytes bearing different linear aromatic density

The importance of the linear aromatic density of polyelectrolytes on the ability to bind and influence the state of aggregation of dyes such as rhodamine 6G is highlighted. The corresponding complexes present different interaction patterns with metal ions such as Cu²⁺, undergoing different spectroscopic changes. The chemical bases of these changes are discussed. The different polyelectrolytes studied, poly(sodium 4-styrenesulfonate), poly(sodium 4-styrenesulfonate-co-sodium maleate) at two different comonomer compositions (3:1 and 1:1), and poly(sodium acrylate-co-sodium maleate), bear different linear aromatic density and induce different R6G binding patterns, as seen by diafiltration and UV–vis spectroscopy of absorbance and fluorescence. As the linear aromatic density increases, smaller dye aggregates are induced in the systems. Thus, in the presence of a large excess of the polyelectrolyte showing the highest linear aromatic density, the dyes disperse on the polymer domain and no aggregation is detected. The interaction is less sensitive to the cleaving effect produced by the addition of NaCl 0.1M for the complexes that include the polyelectrolytes with the highest linear aromatic density. In the presence of Cu²⁺, the complexes formed with the polyelectrolytes showing the lowest linear aromatic density tend to cleave, producing the release of the dye from the polymer domain. On the contrary, the complexes formed with the polyelectrolytes showing the highest linear aromatic density effectively retain the dye in the presence of the divalent metal ion. Based on fluorescence changes by the addition of different amounts of Cu²⁺ to the solution, the potential of the polyelectrolyte/R6G complexes in applications as sensing materials is discussed.     

Structural characterization of Saudi Arabian heavy crude oil by n.m.r. spectroscopy

Saudi Arabian heavy crude oil was separated into six fractions, including five distillate fractions (<93, 93–204, 204–260, 260–343 and 343–454 °C) and a >454 °C distillation residue. Each fraction was analysed by ¹H and ¹³C n.m.r. spectroscopy, and combined gained information from these analyses provided reliable average structural parameters. These included estimation of aliphatic and aromatic content, average paraffinic chain length, and estimation of hydrogen, methyl and alkyl bearing aromatic carbons for each of the six fractions. The extent of branching in paraffinic chains and amount of aromatic bridgehead carbons were also calculated.     

Trapping of Aromatic Compounds by Adsorption on Hydrophobic Sorbents

Abstract

Trapping by adsorption on hydrophobic porous polymers was the selected method for removing aromatic compounds from aqueous diluted medium. The study was done with four aromatic compounds which are often found in foods and which play a role in organoleptic qualities at low concentrations: ethyl acetate, 2,5-dimethylpyrazine, 1-octen 3-ol, and-γ-decalactone. Several sorbents were tested: activated carbon and three porous polystyren-type polymers (Porapak Q, Chromosorb 105, and Amberlite XAD-4). Kinetic and equilibrium sorptions were investigated. The adsorption isotherms were determined for the four aromatic and all the adsorbents, and equilibrium data were correlated with a Freundlich or a Langmuir-type of isotherm equation. Kinetic experimental results were simulated for 1-octen 3-ol using an internal-external mass transfer resistance model. Good agreement was observed for the diffusion coefficient in the sorbent in the range of 10^?8cm^2.s^?1.     

Organoiron Polyelectrolytes: Synthesis and Characterization of Cationic Cyclopentadienyliron Complexes of Polyarylether-Imines

The synthesis of an aromatic ether complex of cyclopentadienyliron containing two terminal aldehyde groups was achieved via metal-mediated nucleophilic aromatic substitution reactions. This dialdehyde monomer was subsequently reacted with a variety of aliphatic and aromatic diamines to produce the corresponding soluble cationic organoiron polyether-imines. These cationic organometallic polymers were characterized using IR, ¹H, and ¹³C NMR, viscosity and thermogravimetric analysis. Viscosity measurements showed that these polymers exhibited polyelectrolyte effects in DMSO solutions. Thermogravimetric analysis showed that decoordination of the iron moieties occurred at about 300°C for polymers with aliphatic spacers in their backbones, while the cyclopentadienyliron moieties were cleaved from the polymers with aromatic spacers in their backbones at about 200°C. Photolytic demetallation of the organoiron polymers resulted in the removal of the pendent cyclopentadienyliron moieties and allowed for the isolation of their organic analogs. While the organoiron polymers were soluble in polar organic solvents, the corresponding organic polymers exhibited very limited solubilities or were insoluble. The organic polymers had glass transition temperatures between 101 and 120°C     

Study of the coupling reactions between electrochemically generated aromatic radical anions and methyl, alkyl and benzyl radicals

Alkyl radicals produced in the indirect reduction of alkyl halides or alkyldimethylsulfonium salts by electrochemically generated aromatic radical anions couple fast with the latter and alkylated or dialkylated dihydro compounds are formed. Rate constants measured for the coupling reaction between on one hand methyl, primary, secondary and tertiary alkyl radicals as well as benzyl and cumyl radicals and on the other hand a wide spectrum of electrochemically generated aromatic radical anions are found to be about 1×10⁹ M⁻¹ s⁻¹. Previous measurements of coupling rate constants for primary alkyl radicals have been re-evaluated since they were affected by the presence of an S_N2 reaction occurring between the alkyl halides used as radical precursors and the aromatic radical anions. New experiments are also included using alkyldimethylsulfonium salts as precursors in order to prevent such S_N2 artefacts. It is concluded that sterical hindrance does not play a significant role for the radical-radical anion coupling reactions. In general the rate constants for the coupling reactions are all close to 10⁹ M⁻¹ s⁻¹.     

Palladium‐Catalyzed Decarboxylative Coupling of α‐ Oxocarboxylic Acids with C(sp2)?H of 2‐Aryloxypyridines

An efficient palladium‐catalyzed decarboxylative ortho‐acylation of 2‐aryloxypyridines with α‐oxocarboxylic acids is described. In this new transformation, the aromatic C(sp²) H bond was successfully acylated to give diverse aromatic ketones regioselectively in moderate to good yields. The pyridine group can be removed easily after the acylation to give the corresponding 2‐hydroxy aromatic ketones.     

Aromatic tertiary carbons as a check on the validity of n.m.r. data on fossil fuels

A method is discussed by which the validity of quantitative data from the ¹H and ¹³C nuclear magnetic resonance analysis of fuel samples can be assessed without the need of internal or external calibrants. In this method the fraction of aromatic tertiary carbon resonances in the ¹³C spectrum is compared with the aromatic atomic hydrogen:carbon ratio obtained from ¹H and ¹³C aromaticity values, and elemental analysis.     

Hydrogenation of aromatic aldehydes to aromatic hydrocarbons over Cu-HZSM-5 catalyst

With benzaldehyde as a model compound, the hydrogenation of aromatic aldehydes to aromatic hydrocarbons was investigated. Cu-HZSM-5 exhibited excellent catalytic performance for the reaction. The obtained catalysts were characterized by N₂ adsorption/desorption, N₂O chemisorptions, X-ray diffraction, NH₃-temperature programmed desorption and X-ray photoelectron spectroscopy. It was found that Cu⁰ active species exhibited poor activity for the hydrogenation of benzene ring, while the strong acidity of HZSM-5 accelerated the hydrogenation reaction via hydrogen spillover phenomenon and the C–O activation effect. In addition, the catalyst was proved to be effective for the hydrogenation of a series of aromatic aldehydes to corresponding aromatic hydrocarbons.     

Reduction of poly(tetrafluoroethylene) by aromatic radical anions: An ESR and NMR study

An ESR and ¹⁹F‐NMR study was carried out to elucidate the reduction kinetics of PTFE with aromatic radical anions (anthracene, benzophenone, biphenyl, and naphthalene), whose counter cation is Na⁺, in THF solvent. The ESR signal intensities of aromatic radical anions decayed according to the second‐order equation whose rate depends on the kind of radical anions; the relative order being naphthalene (1.00) ≫ biphenyl (0.03) > anthracene (0.02) > benzophenone (0.003). The defluorination from PTFE was examined by a high‐resolution ¹⁹F‐NMR method of NaF disolved in an ethanol/water mixed solvent. When an excess amount of Na metal was present, the yield of NaF exceeded the initial concentration of aromatics. The result suggests that the aromatic radical anions are regenerated by the reaction with excess Na metal. The amounts of NaF salts produced during the reducing process were also followed by the same order as the decaying rates of aromatic radical anions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 286–289, 1999     

Synthesis,characterization, and soil biodegradation study of polyamides derived from the novel bioactive diacid monomer 5‐(2‐phthalimidoethanesulfonamido) isophthalic acid

A new bioactive diacid monomer, 5‐(2‐phthalimidoethanesulfonamido) isophthalic acid ( 6 ), was synthesized in three steps. This monomer can be regarded as biologically active aromatic diacid and may be used in the design of biodegradable and biological materials. This monomer was polymerized with several aromatic diamines by step‐growth polymerization to give a series of biodegradable and highly thermally stable polyamides (PAs) with good yield (70–82%) and moderate inherent viscosity between 0.38–0.68 dL/g in a system of triphenylphosphite/pyridine/N‐methyl‐2‐pyrolidone/CaCl_2. The new aromatic diacid 6 and all of the PAs derived from this diacid and aromatic diamines were characterized by Fourier transform infrared, ¹H‐NMR, ¹³C‐NMR, and elemental analysis techniques. The thermal stability of the PAs was determined by thermogravimetric analysis and differential scanning calorimetry techniques under a nitrogen atmosphere, and we found that they were moderately stable. The soil biodegradability behavior of 6 and all of the PAs derived from this diacid and aromatic diamines were investigated in culture media, and we found that the synthesized diacid 6 and all of the PAs were biodegradable under a natural environmental. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011