Reduction of polycyclic aromatic hydrocarbons promoted by cobalt or manganese nanoparticles

A new methodology for the partial reduction of polycyclic aromatic and heteroaromatic hydrocarbons under mild reaction conditions is presented, the process being a reasonable alternative to the catalytic hydrogenation or the Birch reaction. The reduction protocol described is based on the use of cobalt or manganese nanoparticles generated in situ in a simple and economic way, by reduction of commercially available CoCl₂·6H₂O or MnCl₂·2H₂O in the presence of lithium sand and the corresponding PAH, acting itself as an electron carrier. The use of a deuterium-oxide-containing cobalt(II) salt allows the simple preparation of deuterium labeled products. The regiochemistry and degree of reduction in the case of 1-substituted naphthalene derivatives markedly depends on the nature of the metal-NPs used.     

Adsorption of polycyclic aromatic hydrocarbons from aqueous solutions by modified periodic mesoporous organosilica

A novel procedure was developed for the synthesis of a periodic mesoporous organosilica (PMO), which was used to remove polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. Adsorption equilibrium isotherms and adsorption kinetics experiments were carried out in solutions of PAHs (2-60 mg L(-1)), using the PMO as adsorbent. Adsorption models were used to predict the mechanisms involved. The adsorption kinetics data best fitted the pseudo-first-order kinetic model for naphthalene, and to the pseudo-second-order model for fluorene, fluoranthene, pyrene, and acenaphtene. The intraparticle model was also tested and pointed to the occurrence of such processes in all cases. The isotherm models which best represented the data obtained were the Freundlich model for fluoranthene, pyrene, and fluorene, the Temkin model for naphthalene, and the Redlich-Peterson model for acenaphtene. PAHs showed similar behavior regarding kinetics after 24 h of contact between adsorbent and PAHs. FTIR, XRD, BET, and SEM techniques were used for the characterization of the adsorbent material.     

改进QuEChERS-气相色谱-质谱法快速分析测定农用土壤中多环芳烃

建立农用土壤中16种多环芳烃的改进QuEChERS快速提取净化方法及气相色谱-质谱检测方法,并通过对西安市周边农用土壤样品的分析,调查土壤中多环芳烃的污染情况.土壤样品用KOH饱和的甲醇碱化处理后,用丙酮-正已烷(1+1)为提取溶剂,涡旋混匀后超声提取,提取液按改进QuEChERS方法加入无水MgSO4、硅胶及正丙基乙二胺(PSA)进行净化,检测时选用DB -5 MS(30m×0.25 mm×0.25 μm)色谱柱分离,EI电离源及离子监测模式检测,16种多环芳烃的测定低限0.7～3.2μg/kg,加标回收率79.8％ ～ 109.6％,相对标准偏差均低于9.4％.检测的农用土壤样品中均检出有不同程度的多环芳烃残留,约16.7％的土壤样品为轻度污染.     

Analysis of nitrated polycyclic aromatic hydrocarbons

Many nitrated polycyclic aromatic hydrocarbons (NPAH) that are present in low concentrations in the environment and in emission sources have been shown to be mutagenic and/or carcinogenic. This paper reviews the current methods of analysis of these compounds with the emphasis on NPAH measurements in ambient particulate matter samples.     

Method for determination of polycyclic aromatic hydrocarbons by fluorodensitometry

A TLC fluorodensitometric method for the determination of total PAHs in aqueous and hydroalcoholic solutions at the parts per billion level has been developed. The PAHs are extracted into cyclohexane and separated as a class on a chemically bonded reversed-phase TLC plate using stepwise development. In the fluorescence scanning of the plate the PAHs are located by reference to a mixture of 16 PAHs designated by EPA as primary pollutants and measured as benzo(a)pyrene.     

Palladium-catalyzed pentannulation of polycyclic aromatic hydrocarbons

We present a new and versatile one-step synthesis of a series of small molecular chromophores based on cyclopentannulated polycyclic aromatic hydrocarbons (PAH). Easily available pyrene, anthracene, and perylene bromides serve as starting materials for the reactions. The formation of the five-membered ring is achieved by the straightforward palladium(0)-catalyzed carbannulation with various substituted acetylenes. This approach is applicable either to single or multiple annulation procedures leading to hitherto inaccessible PAH topologies. According to the resulting products of the diverse reactions, a mechanistic explanation is proposed. UV/Vis absorption as well as cyclovoltammetric measurements were performed for characterization demonstrating the value of this annulation technique. Optical absorptions of up to 780 nm and absorption coefficients ranging from 8000 to 34,000 M(-1) cm(-1) were detected.     

Simplified determination of polycyclic aromatic hydrocarbons

Accurate quantitative analysis for selected polycyclic aromatic hydrocarbons present on urban dust can be obtained by using a simple procedure consisting of sonic-probe extraction with cyclohexane; clean-up with Florisil((R))-XAD-4((R)), and measurement by high-resolution gas chromatography with flame-ionization detection (HRGC/FID). The analysis can be further simplified by eliminating the clean-up step if HRGC/electron-impact mass-spectrometry (MS) is available. Both the FID and MS methods give results consistent with those obtained by standard procedures. The direct HRGC/MS procedure, combined with chemical ionization, can also be applied to the determination of polycyclic organic materials present in solvent-refined coal, shale oil and crude oil.     

The characterization of polycyclic aromatic hydrocarbons by Raman spectroscopy

High quality Raman spectra, substantially free from fluorescence interference, have been obtained from 11 polycyclic aromatic hydrocarbons, in the solid state, using a Fourier Transform spectrometer. These spectra are rich in sharp bands and, merely by utilizing the limited number of strong peaks it is possible to characterize each hydrocarbon uniquely. The presence of an appreciable number of peaks of medium intensity in each spectrum considerably increases the specificity. The scope and limitations of these spectra for analytical purposes are discussed.     

Oxidation of polycyclic aromatic hydrocarbons catalyzed by soybean peroxidase

Soybean peroxidase (SBP) catalyzes the oxidation of a variety of polycyclic aromatic hydrocarbons (PAHs) in the presence of water-miscible organic cosolvents, including acetonitrile, tetrahydrofuran, and dimethylformamide (DMF). Oxidation was optimal at pH 2.0–2.5, with substantially lower reactivity at pH 1.5 as well as at pH > 3.0. Despite the low pH activity optimum, SBP had an observed half-life of 120 h at pH 2.5. Conversions of greater than 90% were observed with anthracene and 9-methylanthracene in the presence of 50% (v/v) DMF. Anthracene oxidation yielded exclusively anthraquinone, thereby demonstrating that SBP catalyzes a formal six-electron oxidation of the unactivated aromatic substrate to the quinone. A mechanism is proposed to account for this reaction that includes the initial one-electron oxidation of the PAH followed by addition of water to the oxidized PAH. 9-Methylanthracene was more reactive than anthracene, and its enzymatic oxidation yielded two products: anthraquinone and 9-methanol-9,10-dihydroanthracene. The former product indicates that loss of the methyl group occurs during enzymatic oxidation. These results suggest that SBP could be useful in the conversion of PAHs into more environmentally benign materials.     

Differential calorimetric study of polycyclic aromatic hydrocarbons

The temperature, enthalpy, entropy of melting and crystal transitions of 21 polycyclic aromatic hydrocarbons, containing from 2 to 6 unsubstituted condensed rings, were determined by differential scanning calorimetry. The temperature and the molar entropy of melting generally increase with increasing degree of symmetry and molecular size of the hydrocarbon. Apparent deviations from this trend are discussed in terms of molecular distorsion due to steric interaction between neighbouring hydrogens.     

Enthalpies of formation of polycyclic aromatic hydrocarbons

Comparison of the experimental enthalpies of formation of 77 polycyclic aromatic hydrocarbons with those calculated by semiempirical quantum-chemical methods showed that the AM1 approximation ensures the best agreement between the experimental and calculated values. The enthalpies of formation of 60 compounds of this series were calculated using the AM1 method and the corresponding linear regression equation.     

Detection of particulate polycyclic aromatic hydrocarbons by laser-induced time-resolved fluorescence

Summary Laser-induced fluorescence is introduced as an analytical technique for the detection of particle-bound PAHs, which can be found as a result of most combustion processes. A quartz fiber is used to couple the light of a frequency-doubled excimer-pumped dye laser into the sensor head. The fluorescence light is detected using collecting optics, a set of interference filters and a photomultiplier. PAHs in different forms (crystalline, as homogeneous particles and coated on NaCl particles) were investigated. Fluorescence spectra and time-resolved signals, which exhibit characteristic decay times, are presented.     

Far-infrared spectroscopy of small polycyclic aromatic hydrocarbons

Both experimental and theoretical spectroscopic studies on small gas phase polycyclic aromatic hydrocarbons in the far-infrared spectral region are reported. The experimental set-up based on thermal emission and Fourier transform far infrared analysis led to the detection of relatively broad vibrational bands, unresolved in rotation, representative of each molecule. Detailed theoretical investigations were performed, including both ab initio calculations and spectral simulations. For the majority of the samples, this study provides the first detection of the vibrational modes associated with the skeleton motions.     

The spectrophotometric determination of polycyclic aromatic hydrocarbons

The determination of polycyclic aromatic hydrocarbons by elution chromatography from alumina columns followed by ultra-violet spectrophotometry has been elaborated for a more extended range of substances than has been published previously. The methods have been standardised and tables of absorption peaks are provided for easy identification of a number of compounds commonly found as traces in combustion products. Recommendations are given for the preparation of samples for determinations by this method, which has been successfully employed for the analysis of carbon blacks, soots, urban air solids, condensible smokes such as tobacco smoke, wood smoke and coal tar. thermal decomposition or pyrolysis products and other substances, such as urban vegetation, soil, tobacco, snuff, smoked food, and surface drainage water, which have been subjected to the action of smokes or other combustion products.     

Heat capacities of liquid polycyclic aromatic hydrocarbons

Liquid heat capacities of 14 aromatic hydrocarbons were measured using a DSC calorimeter. Measurements were performed in the temperature range 100 K above the melting temperature of each hydrocarbon. The lowest and highest temperatures considered were respectively 303 and 692 K. Experimental results were correlated using Benson's group contribution approach. The group parameters determined allow the experimental results to be represented to within 2%.