Xylene

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Polymorphs and pseudopolymorphs of N,N,-dithiobisphthalimide

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2002
Dorcas M. M. Farrell
N,N,-Dithiobisphthalimide, C16H8N2O4S2 (I), forms a wide range of polymorphs and solvates (pseudopolymorphs). When (I) is crystallized from methanol it yields a solvent-free polymorph (4), in Pna21 with Z, = 1, in which the molecules are linked into chains by a single C,H,O hydrogen bond: crystallization from either acetonitrile or dimethylformamide produces a monoclinic polymorph (5), in P21/c with Z, = 2, also solvent-free, in which the molecules are linked into molecular ladders. Nitromethane forms a monosolvate, C16H8N2O4S2CH3NO2 (6), in P21/c with Z, = 1, in which the solvent molecules are linked to the molecules of (I) not only via a conventional C,H,O hydrogen bond but also via a polarized multicentre interaction involving all three C,H bonds of the solvent molecule. Chlorobenzene forms a precise hemisolvate, C16H8N2O4S20.5C6H5Cl (7), in P with Z, = 1, while ethylbenzene forms an approximate hemisolvate 2C16H8N2O4S20.913C6H5C2H50.087H2O (8), in P21/c with eight molecules of (I) per unit cell. In both solvates the molecules of (I) are linked, in (7) by ,,, stacking interactions augmented by weak C,H,O hydrogen bonds and in (8) by stronger C,H,O hydrogen bonds: the solvent molecules lie in isolated cavities, disordered across inversion centres in (7) and fully ordered in general positions in (8). Crystallization of (I) either from tetrahydrofuran or from wet tert -butanol yields isomorphous solvates (9) and (10), respectively, in C2/c with Z, = 0.5, in which molecules of (I) lie across twofold rotation axes and are linked by ,,, stacking interactions and very weak C,H,O hydrogen bonds, forming a framework enclosing continuous channels: highly disordered solvent molecules lie within these channels. p -Xylene and toluene form isomorphous hemisolvates (11) and (12) with unit cells metrically very similar to those of (9) and (10), but in P21/n with Z, = 1: in these two solvates the molecules of (I) are linked into a framework by very short C,H,O hydrogen bonds; the solvent molecules lie within continuous channels, but they are localized across inversion centres so that the toluene is disordered across an inversion centre. [source]


Characterizing the regulation of the Pu promoter in Acinetobacter baylyi ADP1

ENVIRONMENTAL MICROBIOLOGY, Issue 7 2008
Wei E. Huang
Summary Effective gene trapping and screening requires sensory and regulatory compatibility of both host and exogenous systems. The naturally competent bacterium Acinetobacter baylyi ADP1 is able to efficiently take up and integrate exogenous DNA into the chromosome, making it an attractive host system for a wide range of metagenomic applications. To test the ability of A. baylyi ADP1 to express the XylR-regulated Pu promoter from Pseudomonas putida mt-2, we have constructed and examined an A. baylyi ADP1 strain, ADPWH- Pu-lux-xylR. The Pu promoter in ADPWH- Pu-lux-xylR was specifically induced by toluene, m -, p - and o- xylene. The substrate-induced Pu promoter was highly dependent on the growth medium: it was repressed in rich media until stationary phase, but was immediately induced in minimal medium with glucose as the sole carbon source (MMG). However, the Pu promoter was repressed in MMG when it was supplemented with 5 g l,1 yeast extract. Further investigation showed that the Pu promoter in MMG was repressed by 0.5 g l,1 aspartic acid or asparagine, but not repressed by glutamine. Changing the carbon/nitrogen ratios by addition of ammonia did not significantly affect the Pu promoter activity but addition of nitrate did. These results show that A. baylyi ADP1 reproduced characteristics of the XylR-regulated Pu promoter observed in its original host. It demonstrates that A. baylyi could provide an excellent genetic host for a wide range of functional metagenomic applications. [source]


QSARs for aromatic hydrocarbons at several trophic levels

ENVIRONMENTAL TOXICOLOGY, Issue 2 2006
Walter Di Marzio
Abstract Quantitative structure,activity relationships (QSARs) with aromatic hydrocarbons were obtained. Biological response was measured by acute toxicity of several aquatic trophic levels. The chemicals assayed were benzene, toluene, ethylbenzene, o -xylene, m -xylene, p -xylene, isopropylbenzene, n -propylbenzene, and butylbenzene. Acute toxicity tests were carried out with Scenedesmus quadricauda, as representative of primary producers; Daphnia spinulata, a zooplanctonic cladoceran; Hyalella curvispina, a benthic macroinvertebrate; and Bryconamericus iheringii, an omnivorous native fish. The EC50 or LC50 was calculated from analytical determinations of aromatic hydrocarbons. Nonlinear regression analysis between the logarithm of the octanol,water partition coefficient (log Kow) of each compounds and the toxicity end points was performed. QSARs were positively related to increases in log Kow at all trophic levels. Intertaxonomic differences were found in comparisons of algae with animals and of invertebrates with vertebrates. We observed that these differences were not significant with a log Kow higher than 3 for all organisms. Aromatic hydrocarbons with log Kow values of less than 3 showed different toxicity responses, with algae more resistant than fish and invertebrates. We concluded that this was a result of the narcotic mode of action related to liposolubility and the ability of the compound to reach its target site in the cell. The bioconcentration factor (BCF) achieved to start nonpolar narcosis fell almost 1 order of magnitude below the BCF expected from the log Kow. Predicted critical body residues for nonpolar narcosis ranged between 2 and 1 mM. 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 118,124, 2006. [source]


Toxicity tests to assess pollutants removal during wastewater treatment and the quality of receiving waters in Argentina

ENVIRONMENTAL TOXICOLOGY, Issue 3 2001
Carlos E. Gmez
Abstract In Argentina, legislation to control adverse impacts of effluent discharges and the quality of receiving waters is scant and relies mainly on the physicochemical characteristics of the effluents and receiving waters. Objectives of this study were to use standardized acute toxicity tests to assess treatment of petrochemical industry effluents and the toxicity of various treated industrial effluents in the Buenos Aires metropolitan area and their receiving waters. Tests for the first objective used Daphnia magna and Ceriodaphnia dubia; those for the second used D. magna, Spirillum volutans, and Scenedesmus spinosus. Chemical analyses demonstrated that the removal of aromatic hydrocarbon compounds (benzene, toluene, ethylbenzene, xylene, styrene, and naphthalene) from the petrochemical effluents ranged between 77 and 93%, but toxicity removal was significantly lower: untreated effluents were very toxic and treated effluents were very toxic to toxic [acute toxicity units (TUa)>3]. Physicochemical parameters measured according to current Argentinian regulations indicated that industrial effluents (e.g., from textile and paper industries) were within established guidelines, but 25% of the samples were moderately to highly toxic (TUa>1.33). However, for the receiving waters, toxicity tests were moderate to very toxic. The results show the need of including tests for toxicity of discharged effluents, and their effects on receiving waters of Argentina, especially for regulatory purposes. 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 217,224, 2001 [source]


Emerging pollutants in the North Sea in comparison to Lake Ontario, Canada, data

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2007
Jens Arne Andresen
Abstract In the present study, the concentrations and fate of contaminants such as organophosphate flame retardants and plasticizers, musk compounds such as galaxolide (HHCB), tonalide (AHTN), musk ketone and musk xylene, the bactericide triclosan, as well as the metabolites HHCB-lactone and triclosan-methyl were compared in the aqueous phase of the German Bight (North Sea). The concentrations of these compounds were around 1 to 10 ng/L in nearshore areas, and the concentrations were lower in the more pristine areas. The highest concentrations were determined for tris-(2-chloro- isopropyl) phosphate in the North Sea with concentration exceeding 10 ng/L even for the offshore samples. The samples contained 1 to 20 ng/L chlorinated organophosphates, approximately 1 ng/L nonchlorinated organophosphates, and 0.3 to 3 ng/L fragrance compounds. Some samples from Lake Ontario (Canada) were analyzed in comparison. Per capita emissions were calculated for both regions. These emissions were compared and turned out to be very similar for the Canadian and German locations. For the North Sea, some observations concerning stability, dilution, and degradation, as well as sources of the respective substances, were performed. These data indicate that the chlorinated organophosphates and some musk fragrances exhibit half lives exceeding the residence times and thus can be considered to be persistent in this ecosystem. In the German Bight, the river Elbe is the dominating source for the more hydrophilic compounds, such as chlorinated organophosphate flame retardants, which are diluted only into the North Sea. However, for the more lipophilic compounds such as the musk fragrances, different input patterns as well as distribution patterns are relevant, though the river Elbe is still a major source of pollution to the German Bight of the North Sea. The data seem to indicate either relevant inputs further west of the sampling area or mobilization from the sediments. [source]


A thermodynamics-based estimation model for adsorption of organic compounds by carbonaceous materials in environmental sorbents

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2003
Paul C. M. van Noort
Abstract A model was developed to estimate Langmuir affinities for adsorption of low-polarity organic compounds from either water or air by carbonaceous sorbents. Sorption enthalpies and entropies provided the basic information for the description of sorption affinities in terms of the entropy of melting and either solubility in water or vapor pressure. For m -xylene, polycyclic aromatic hydrocarbons (PAHs) and chlorobenzenes on 10 different sorbents, 80% of the measured sorption affinities fall within a factor of four of the model estimates. Equations for the limiting distribution coefficients in terms of either octanol,air (KOA) or octanol,water partition (Kow) coefficients were derived from regressions of calculated affinities combined with an estimated relation between experimental Langmuir sorption capacities and Kow. Estimated soot,water distribution coefficients were within a factor of three of measured data for polychlorobiphenyls (PCBs) and lower molecular weight PAHs on automotive soot samples and captured the dependence of PCB distribution coefficients on the extent of ortho substitution. For higher molecular weight PAHs, sorption was underestimated. For soot in sediment,water distribution coefficients of PAHs and PCBs, estimated values captured both the trend of measured data with Kow and the dependence on sorbate planarity. Tentative application to aerosol,air distribution explained the observed independence of distribution coefficient,KOA relations for PCBs on the extent of ortho substitution and suggested nonequilibrium conditions for PAHs in comparison with recent measurements. [source]


Mechanisms affecting the dissolution of nonaqueous phase liquids into the aqueous phase in slow-stirring batch systems

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2001
Mathias Schluep
Abstract Understanding the kinetics of the exchange processes between nonaqueous phase liquids (NALs) and water is important in predicting the fate of anthropogenic compounds such as petroleum hydrocarbons, i.e., benzene, toluene, ethylbenzene, and xylene (BTEX) as well as polynuclear aromatic hydrocarbons (PAHs). Exchange processes occurring in the environment resemble the experimental setup of the slow-stirring method (SSM) designed to determine solubilities and octanol-water partition coefficients. Data obtained from SSM experiments for diesel fuel compounds are interpreted by a linear transfer model that is characterized by an aqueous molecular boundary layer and the water/NAPL equilibrium partition coefficient. For the chosen experimental setup, the boundary layer thickness is 2.42 10,2 cm. Typical equilibration times lie between 1 and 2 d. Due to the temperature dependence of the aqueous diffusivity, this time increases with decreasing temperature. Transport within the NAPL phase can slow down the exchange process for the more water-soluble compounds (e.g., benzene) provided that the stirring rate exceeds a critical value. [source]


Photophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer Blends

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Christopher R. McNeill
Abstract Here, studies on the evolution of photophysics and device performance with annealing of blends of poly(3-hexylthiophene) with the two polyfluorene copolymers poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,,2,,-diyl) (F8TBT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. In blends with F8TBT, P3HT is found to reorganize at low annealing temperatures (100,C or below), evidenced by a redshift of both absorption and photoluminescence (PL), and by a decrease in PL lifetime. Annealing to 140,C, however, is found to optimize device performance, accompanied by an increase in PL efficiency and lifetime. Grazing-incidence small-angle X-ray scattering is also performed to study the evolution in film nanomorphology with annealing, with the 140,C-annealed film showing enhanced phase separation. It is concluded that reorganization of P3HT alone is not sufficient to optimize device performance but must also be accompanied by a coarsening of the morphology to promote charge separation. The shape of the photocurrent action spectra of P3HT:F8TBT devices is also studied, aided by optical modeling of the absorption spectrum of the blend in a device structure. Changes in the shape of the photocurrent action spectra with annealing are observed, and these are attributed to changes in the relative contribution of each polymer to photocurrent as morphology and polymer conformation evolve. In particular, in as-spun films from xylene, photocurrent is preferentially generated from ordered P3HT segments attributed to the increased charge separation efficiency in ordered P3HT compared to disordered P3HT. For optimized devices, photocurrent is efficiently generated from both P3HT and F8TBT. In contrast to blends with F8TBT, P3HT is only found to reorganize in blends with F8BT at annealing temperatures of over 200,C. The low efficiency of the P3HT:F8BT system can then be attributed to poor charge generation and separation efficiencies that result from the failure of P3HT to reorganize. [source]


Electroluminescence and Laser Emission of Soluble Pure Red Fluorescent Molecular Glasses Based on Dithienylbenzothiadiazole

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
Ju Huang
Abstract Soluble molecular red emitters 1a/1b are synthesized by Stille coupling from 2-(3,5-di(1-naphthyl)phenyl)thiophene precursors. The compounds show emission maxima at ca. 610,nm in CH2Cl2 solution and 620,nm in solid films. Replacing the n -hexyl substituent by 4- sec -butoxyphenyl produces a marked increase of glass transition temperature (Tg) from 82,C to 137,C and increases the solubility in toluene and p -xylene, thus improving the film-forming properties. Cyclic voltammetry shows that the compounds can be reversibly oxidized and reduced around +1.10 and ,1.20,V, respectively. A two-layered electroluminescent device based on 1b produces a pure red light emission with CIE coordinates (0.646, 0.350) and a maximal luminous efficiency of 2.1,cd A,1. Furthermore, when used as a solution-processed red emitter in optically pumped laser devices, compound 1b successfully produces a lasing emission at ca. 650,nm. [source]


Cell surface hydrophobicity of Candida albicans isolated from elder patients undergoing denture-related candidosis

GERODONTOLOGY, Issue 2 2009
Roberta Diavana De Souza
Background:, The virulence potential of Candida albicans strains enrolled in denture-related candidosis still remains uncertain. Candida albicans cells with higher cell surface hydrophobicity (CSH) rates, so-called hydrophobic, present higher adhesion success in different host tissues than cells with lower rates, or even hydrophilic. Objective:, The proposition of this study was to evaluate the differences in the CSH of strains isolated from denture users with and without denture-related candidosis. Material and methods:, The strains were obtained from two paired groups of patients living a same retirement house. Fungal cells were submitted to CSH evaluation by the hydrocarbon partition test using xylene. Results:, The measures revealed that the yeasts from patients with candidosis had CSH values ranging from 4.52% to 12.24%, with an average of 8.22 2.92%. In the countergroup, the CSH ranged from 3.86% to 14.36%, with an average of 8.38 3.76%. The difference between the groups were considered not relevant (p = 0.997). Conclusion:, The results let to the inference that natural populations of C. albicans from patients with and without clinical manifestation denture-related candidosis do not differ one from the other regarding to CSH. [source]


Contaminant Transport in Fractured Chalk: Laboratory and Field Experiments

GROUND WATER, Issue 6 2003
K. Witthser
Laboratory experiments were performed on chalk samples from Denmark and Israel to determine diffusion and distribution coefficients. Batch tests were used to define sorption isotherms for naphthalene and o-xylene. Linear sorption isotherms were observed and described with Henry-isotherms. Because of the high purity and low contents of clay minerals and organic carbon, Danish and white Israeli chalk generally have low retardation capacities. Con-trarily, gray Israeli chalk, with organic carbon fractions as high as 1.092%, remarkably retards organic contaminants. The Koc concept is not applicable to predicting distribution coefficients based on the organic carbon content in the chalk samples. Effective diffusivities of o -xylene, naphthalene, and several artificial tracers were determined using through-diffusion experiments. Based on measured diffusion coefficients and available literature values, a chalk specific exponent of 2.36 for Archie's law was derived, allowing a satisfactory estimate of relative diffusivities in chalk. A field-scale tracer test with uranine and lithium was performed in the Negev desert (Israel) to examine the transfer-ability of diffusivities determined on small rock samples in the laboratory. Due to low recovery rates of the tracer, a modified single fissure dispersion model was used for inverse modeling of the breakthrough curves. Resulting diffusivities deviate insignificantly from the laboratory values, which are considered to be representative for the investigated part of the aquifer and applicable in transport models. [source]


Vapor Intrusion in Homes over Gasoline-Contaminated Ground Water in Stafford, New Jersey

GROUND WATER MONITORING & REMEDIATION, Issue 1 2006
Paul F. Sanders
The potential for chemical vapor intrusion from contaminated ground water to the interior of homes was investigated at a site with a leaking underground gasoline storage tank in Stafford Township, New Jersey. This location exhibited conditions favorable to vapor intrusion, with sand soil and a water table depth of 3.3 m. Concentrations of volatile organic chemicals in the ground water were as high as 82 mg/L for total benzene, toluene, ethylbenzene, and xylene (BTEX) and up to 590 mg/L for methyl- t -butyl ether (MTBE). Soil vapor samples at multiple depths were taken adjacent to several homes. Inside the homes, air samples were taken on the main floor, in the basement, and under the foundation slab. Despite high ground water concentrations, only one home had measurable impacts to indoor air quality attributable to some of the ground water contaminants. In this house, the BTEX chemicals were not detected in the basement, indicating a lack of indoor air impacts from the ground water for these chemicals. Oxygen measurements suggested that degradation attenuated these chemicals as they diffused through the vadose zone. However, MTBE, 2,2,4-trimethylpentane (isooctane), and cyclohexane were found in the indoor air. The first two of these chemicals served as gasoline-specific tracers and indicated that vapor intrusion was occurring. Attenuation factors (the ratio of the indoor air concentration to a source soil vapor concentration) for the BTEX chemicals between the ground water and the indoor air were <1 10,5, and for MTBE was 1.2 10,5. Attenuation factors between the deep-soil vapor and the basement air were as follows: BTEX compounds, <1 10,5; MTBE, 2.2 10,5; 2,2,4-trimethylpentane, 3.6 10,4; and cyclohexane, 1.2 10,4. Attenuation factors between the subslab vapor and the basement air were 7 to 8 10,3. [source]


Diffusion Characteristics of VOCs Indoors

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2010
Shin-ichi Shibata Student Member
Abstract Diffusion characteristics of volatile organic compounds (VOCs) were investigated indoors using tin oxide gas sensors. The chemicals cause various kinds of symptoms in humans, for example, the sick house syndrome. In this study, eight sensors were installed in a vertical direction and on a plane surface. These sensors were of the same type. The VOC is placed in a generation source, and the sensor output increases as the chemical diffuses. The sensor output becomes higher as the concentration increases. The following chemicals were tried as air pollutants: formaldehyde, toluene, and xylene. The sensor output changes in short, quick steps by slight fluctuations of the wind velocity. Therefore, the differential characteristic of the sensor output was adopted and the noise component was removed as far as possible. A threshold time tth to the characteristic was set up. It is assumed that the examining chemical reaches the installed sensor point in a time greater than this time. The new speed of arrival is proposed using the threshold time. The speed s [cm/min] is indicated using the distance d and the reaching time tth, namely, s = d/tth. Here, d means the distance between the sensor position and the polluting source. As a result, the speed for the sensor that is installed near the ceiling (at a height of 260 cm from the floor) is the highest. And, it became obvious that s was larger for the chemical with a smaller molecule. The speed of formaldehyde for the sensor installed near the ceiling was 700 cm/min and that for the sensor installed at the height of 100 cm from the floor was 370 cm/min. There is almost a two times difference in the speed. Copyright 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]


Prevention of Manganese Precipitation during the Continuous Selective Partial Oxidation of Methyl Aromatics with Molecular Oxygen in Supercritical Water

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009
Joan Fraga-Dubreuil
Abstract Presented here is an investigation of the activity and recovery of the homogeneous manganese/bromide catalyst during the continuous flow oxidation of o -xylene, as model substrate, with molecular oxygen (O2) in supercritical water (scH2O). Two strategies are discussed for preventing catalyst precipitation, mainly in the form of oxides such as manganese(IV) oxide, The first strategy involves varying the manganese:bromide ratio using either manganese(II) acetate or manganese(II) bromide in the presence of hydrobromic and other acids. The results show that the effect of acidity and bromide concentration plays an important role in preventing the manganese/bromide catalyst from precipitating. The second strategy uses aromatic carboxylic acids in combination with the manganese/bromide catalyst, particularly benzoic acid, which improves the catalyst recovery dramatically over a certain range of acid concentrations. Our studies show how the presence of an organic acid and/or its precursors is important in stabilising the catalyst. Our results are rationalised on the basis of a tentative reaction mechanism. [source]


Highly Efficient Halogenation of Organic Compounds with Halides Catalyzed by Cerium(III) Chloride Heptahydrate Using Hydrogen Peroxide as the Terminal Oxidant in Water

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009
Habib Firouzabadi
Abstract In this article a new environmentally friendly catalytic method is described for the efficient monoiodination and bromination of arenes and also iodoetherification and iodolactonization of olefins using hydrogen peroxide as the terminal oxidant. The method is based on using sodium iodide or sodium bromide, hydrogen peroxide (35%) and cerium(III) chloride as an effective catalyst in water at room temperature or under reflux conditions. By this protocol, iodination of anilines proceeded with high regioselectivity at the para position with the formation of small amounts of the ortho isomers. However, bromination of anilines proceeded with absolute regioselectivity to give the para isomers as the sole products in high yields. Iodinations and brominations of m -xylene, toluene, chloro- and bromobenzenes were proceeded with excellent regioselectivity to produce the para isomers as the sole products. Benzene was also halogenated by this catalytic system to give the monohalogenated benzene in good yields. Iodoetherification and iodolactonization of olefins also proceeded easily in high yields at room temperature. However, the bromination of olefins by this protocol failed and the starting materials were detected intact. [source]


New Synthetic Approach to a [1.1.6] Metapara Cyclophane Derivative via Suzuki,Miyaura Cross-Coupling and Ring-Closing Metathesis,

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005
Sambasivarao Kotha
Abstract The synthesis of a [1.1.6] metapara cyclophane derivative, 1,5(1,4),3(1,3)-tribenzenacycloundecaphan-8-ene-6,11-dione, has been achieved via the Suzuki,Miyaura cross-coupling of ,,,,-dibromo- m -xylene with an arylboronic acid derivative followed by an allylation and ring-closing metathesis reaction sequence. [source]


High temperature copolymerization of styrene/ethyl acrylate: Reactivity ratio estimation in bulk and solution

ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2004
Nahla Sahloul
Abstract Styrene/ethyl acrylate (Sty/EA) free-radical copolymerizations have been conducted in bulk with and without initiator and in solution using p -xylene and m -xylene (30 wt% and 60 wt% solvent level) at 100C and 130C. The monomer reactivity ratio values and their temperature dependence have been determined from low conversion copolymer composition data using the computer software package RREVM, which is based on the error in variables model (EVM) method. Copolymer composition data at low conversion confirmed the Mayo,Lewis model at both temperatures. The reactivity ratio values of the Sty/EA system do not seem to change with dilution by nonpolar solvents at low concentration from the reactivity ratio values obtained in bulk with and without initiator. However, xylene isomers were found to have a slight effect on the reactivity ratio value of ethyl acrylate when high solvent concentration was utilized. 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 186,195, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20009 [source]


Free radical graft copolymerization of poly(n -butyl methacrylate) and poly(butyl acrylate) onto chlorinated rubber: Characterization and mechanical properties,

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2004
Shanaz Ahmed
Abstract Graft copolymerization of n -butyl methacrylate and butyl acrylate onto chlorinated rubber was carried out in solution medium (xylene) using benzoyl peroxide as initiator. The chlorinated rubber-g-(n -butyl methacrylate- co -butyl acrylate) (CR-g-nBMA- co -BA) was isolated from the copolymerization mixture by extracting with isopropyl ether. Infrared (FT-IR) spectra, proton nuclear magnetic resonance (1H NMR) and thermogravimetric analysis of the graft copolymer showed the occurrence of grafting. Percent grafting and grafting efficiency calculated under different experimental conditions are discussed. The mechanical properties of the grafted CR films were studied under different strain rates. 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 103,110, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20003 [source]


Hydrocarbon degradation by thermophilic Nocardia otitidiscaviarum strain TSH1: physiological aspects

JOURNAL OF BASIC MICROBIOLOGY, Issue 6 2007
Majid Zeinali
Abstract Indigenous thermophilic hydrocarbon degraders are of special significance for the bioremediation of oil-contaminated desert soils with ambient temperature of 45,50 C. The first objective of this study was to demonstrate the hydrocarbon-degrading capability of Nocardia otitidiscaviarum TSH1 (DSM 45036) which grows optimally at 50 C. Analysis of the metabolic profile of the strain TSH1 showed that it could metabolize phenol, intermediate-chain-length n -alkanes and some polycyclic aromatic hydrocarbons (PAHs) ranging in size from two to four fused rings efficiently, but not toluene and xylene. N. otitidiscaviarum TSH1 was able to survive and grow at phenol concentrations up to 875 mg l,1. For the first time, the physiological response of a thermophilic Nocardia strain to poorly available hydrophobic compounds was also investigated. When grown on a mineral salt medium with hexadecane, N. otitidiscaviarum TSH1 showed very high affinity for the organic phase. Additionally, PAH-grown cells were considerably hydrophobic. The capacity of PAH-utilizing N. otitidiscaviarum TSH1 isolate to produce biosurfactants was also investigated. Fatty acids (C14,C18) were detected by GC-MS analysis during bacterial growth in PAH supplemented mineral media. High cell surface hydrophobicity and capability of N. otitidiscaviarum TSH1 to degrade different hydrocarbons at 50 C may make it an ideal candidate to treat oil-contaminated desert soils. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Molecular and histological responses in rat skin exposed to m -xylene,

JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 2 2003
Palur G. Gunasekar
Abstract Solvents, surfactants, cutting fluids, hydrocarbons, and oils cause skin irritation by incompletely understood mechanisms. This study examined histological and molecular changes in rodent skin caused by brief topical exposures to m -xylene. At 0, 1, 2, 4, and 6 h after 1-h exposure, skin samples were removed and analyzed for histopathological changes and interleukin-1, (IL-1,) and inducible nitric oxide synthase (iNOS) protein levels. Histopathological changes (epidermal,dermal separation and granulocyte infiltration) and increases in IL-1, and iNOS protein expression occurred during our observation period. IL-1, levels increased by 80% immediately after exposure and iNOS levels increased about 60% 4 hours after exposure. Our study demonstrates that dermal exposure to m -xylene promotes IL-1, and iNOS production in skin and these proteins may serve as early indicators of skin irritation. 2003 Wiley Periodicals, Inc. J Biochem Mol Toxicol 17:92,94, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.10065 [source]


Long-term performance of co-metabolic degradation of trichloroethylene in a fluidized bed reactor fed with benzene, toluene and xylene

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2008
Wei-Min Wu
Abstract BACKGROUND: Trichloroethylene (TCE) can be degraded under aerobic condition with toluene and other aromatic compounds. Inhibition by primary substrates and toxicity of TCE oxidation influence TCE degradation. RESULTS: Long-term co-metabolic degradation of TCE was evaluated using a laboratory-scale fluidized bed reactor (12 L) with granular activated carbon (1.57 kg) as media and activated sludge as inoculum. The reactor was fed with TCE and a mixture of benzene, toluene and xylene (BTX) and operated with one-pass (hydraulic retention time (HRT) of 5,6 min) for 6 months and then with recirculation (HRT of 20,30 min) for 18 months. BTX/TCE-degrading biofilm was developed within 1 month. TCE was effectively degraded with influent TCE concentrations from 48 to 280 g L,1. BTX inhibited TCE degradation. Recirculation (or long HRT) increased TCE removal efficiency from 30% with one-pass to 90%. BTX/TCE load ratio influenced TCE removal efficiency and TCE/BTX removal ratio. TCE degradation fitted first-order kinetics. The biomass grown in the reactor also degraded cis -1,2-dichloroethylene (DCE), trans -1,2-DCE and vinyl chloride efficiently except for 1,1-DCE. CONCLUSION: Co-metabolic degradation of TCE by BTX-degrading biomass from activated sludge is sustainable in the long term. BTX/TCE load ratio is a key parameter for TCE removal performance. Copyright 2008 Society of Chemical Industry [source]


Removal of TEX vapours from air in a peat biofilter: influence of inlet concentration and inlet load

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2006
Carmen Gabaldn
Abstract This paper presents the results of the study of the removal of toluene, ethylbenzene, and o -xylene (TEX) by biofiltration using a commercial peat as filter-bed material. Runs with a single organic compound in air, and with the mixture of TEX in air, were carried out for at least 55 days in laboratory-scale reactors inoculated with a conditioned culture. The influence of organic compound inlet load and of gas flow rate on the biofilter's performance was studied, including relatively high values of pollutant inlet concentration (up to 4.3 gC m,3 for ethylbenzene, 3.2 gC m,3 for toluene, and 2.7 gC m,3 for o -xylene). Results obtained show maximum elimination capacities of 65 gC m,3 h,1 for o-xylene, 90 gC m,3 h,1 for toluene, and 100 gC m,3 h,1 for ethylbenzene, and high removal efficiency (>90%) even for moderately elevated concentrations: 3.0, 2.5 and 1.8 gC m,3 for ethylbenzene, toluene and o -xylene, respectively. The behaviour of the TEX mixture was in good agreement with the results obtained for the runs in which only one organic compound was present. Ethylbenzene and toluene are degraded easier than o -xylene, and inhibitory effects due to the presence of multiple substrates were not observed. Copyright 2005 Society of Chemical Industry [source]


Liquid,liquid extraction of Hg(II) from acidic chloride solutions using bis-2-ethylhexyl sulfoxide

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2001
Tania Francis
Abstract The liquid,liquid extraction of Hg(II) from acidic chloride solutions has been studied using bis-2-ethylhexyl sulfoxide (B2EHSO) as an extractant. For comparison, extraction studies have also been carried out using di- n -octyl sulfoxide (DOSO) and diphenyl sulfoxide (DPhSO). The extraction data have been analysed by both graphical and theoretical methods taking into account aqueous phase speciation and all plausible complexes extracted into the organic phase. These results demonstrate that Hg(II) is extracted into xylene as HgCl2.3R2SO (where R2SO represents the sulfoxide). The equilibrium constant of the extracted complex has been deduced by non-linear regression analysis. The developed liquid,liquid extraction procedure has been applied for the recovery of mercury from the brine-sludge of a Chlor-Alkali plant. 2001 Society of Chemical Industry [source]


Terephthalic acid synthesis at higher concentrations in high-temperature liquid water.

AICHE JOURNAL, Issue 6 2009

Abstract We synthesized terephthalic acid (TPA) from p -xylene at an initial concentration above its solubility limit in high-temperature liquid water (HTW). The nominal p -xylene loading at the reaction conditions was 0.4 mol L,1, which is the highest reported to date for generation of high TPA yields (>70 mol %) in HTW. The presence of two liquid phases during the reaction did not appear to accelerate the rate, unlike behavior reported for some other organic reactions done "on water" at lower temperatures. Adding oxygen gas in a large increment during synthesis produced a black liquid and a black solid byproduct, which is a previously undocumented problem. Adding oxygen in smaller increments prevented formation of the liquid and solid byproducts and also provided high selectivities (90 mol %) and yields (>70 mol %) of TPA. These results demonstrate the feasibility of HTW as a medium for TPA synthesis at p -xylene concentrations even higher than its solubility limit. 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Application of distillative freezing in the separation of o -xylene and p -xylene

AICHE JOURNAL, Issue 5 2006
Lie-Ding Shiau
First page of article [source]


Effect of gutta-percha solvents at different temperatures on the calcium, phosphorus and magnesium levels of human root dentin

JOURNAL OF ORAL REHABILITATION, Issue 8 2001
H. Do
The aim of this study in vitro investigation was to evaluate the alterations caused by warmed gutta-percha solvents on the calcium, phosphorus and magnesium levels of root dentin. Extracted human anterior teeth, whose crowns and apical root thirds had been removed were used as root dentin specimens. The roots were sectioned longitudinally into two segments, cleaned and dried. Segments were divided into 12 groups (n=12). In 6 groups, the specimens received treatment with the following solvents at room temperature (22 C): Chloroform, xylene, eucalyptol, orange oil, halothane and saline (control). Within each group, the specimens were further subgrouped into two to be incubated (100% humidity at 37 C) for 5 and 10 min, respectively, following treatment with the solvents. The remaining six groups were treated with the same solvents which had been previously warmed to body temperature (37 C) and received the same experimental procedures. The levels of calcium, phosphorus and magnesium in each specimen were analysed using energy dispersive spectrometric microanalysis. Statistical analysis of the readings showed that neither warming of the solvents nor prolonged incubation (treatment) time was capable of altering the histochemical composition of cut root dentin surfaces. [source]


Experimental and theoretical investigation of a new rapid switching near-infrared electrochromic conjugated polymer

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2010
Han-Yu Wu
Abstract A new rapid switching near-IR electrochromic conjugated propeller-shape polymer (PBTPAFL) with lower oxidation potential containing a di-triarylamine group was synthesized via Suzuki coupling approach. The observed UV-vis-NIR absorption changes in the PBTPAFL film at various potentials are fully reversible and associated with strong color changes from the original light green to dark green and then to a Prussian blue. Excellent continuous cyclic stability of the electrochromic characteristics with a rapid color switching time 2.58 s and bleaching time 1.76 s was found as well. Compared with P1 and P2, the introduction of more electron-donating propyl phenyl group in the para position of PBTPAFL lowered the oxidative potential and prevented coupling reaction during the electrochromic procedure. The high molecular weight conjugated polymer having high thermal stability with Td10 more than 450 C has excellent solubility in common organic solvents such as NMP, THF, chloroform, toluene, xylene, and benzene at room temperature (25 C) due to the propeller-shape structure and long alkyl chain on fluorene. Herein, from the combination of the experimental and computational study, we proposed a mechanism on the basis of the molecular orbital theory to explain the electrochromic oxidation behavior. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3913,3923, 2010. [source]


Synthesis and characterization of fluorene-based copolymers containing siloxane or distilbene moieties on their main chain

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2009
Hoon-Je Cho
Abstract Two novel types of polyfluorene copolymers containing siloxane linkages or distilbene moieties on their main-chains were synthesized by Ni(0)-mediated Yamamoto coupling polymerization. These polymers, designated P2Silo05, P2Silo15, PF-P02, and PF-P05 were prepared by copolymerization between 2,7-dibromo-9,9,-dihexylfluorene and bis(bromobenzene)-terminated disiloxane monomer (for P2Silo05 and P2Silo15) or dibromodistilbene monomer (for PF-P02 and PF-P05). All of the polymers were highly soluble in common organic solvents such as chloroform, toluene, and p -xylene. The glass transition temperatures of the polymers were between 92 and 113 C, and the decomposition temperatures for a 5% weight loss (Td) were above 420 C for all of the polymers, demonstrating high thermal stability. The molecular weight (Mw) of the polymers ranged from 4.2 104 to 8.8 104. The blue shift of the maximum in the UV-visible absorption was greater in polymers with a higher molar percentage of siloxane linkages or distilbene moieties than in homo poly (dihexylfluorene) (PDHF). However, the photoluminescence spectra of the polymers were similar to those of PDHF in terms of the onsets and patterns. Single-layer light-emitting diodes were fabricated with a configuration of ITO/PEDOT:PSS/polymers/Ca/Al. The maximum electroluminescence emission wavelengths of the polymers were 425,450 nm, corresponding to pure blue light. The CIE co-ordinates of the polyfluorenes containing siloxane linkages or distilbene moieties ranged from (0.21, 0.21) to (0.17, 0.10), indicating deeper blue light than that of PDHF {CIE co-ordinates of (0.25, 0.29)}, with P2Silo15 giving the deepest blue-light {CIE co-ordinates of (0.17, 0.10)}. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1595,1608, 2009 [source]


Optical properties of a novel fluorene-based thermally stable conjugated polymer containing pyridine and unsymmetric carbazole groups

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2009
Der-Jang Liaw
Abstract A new diiodo monomer containing heterocyclic pyridine and carbazole groups was synthesized via Chichibabin reaction and used in the preparation of a conjugated polymer via Suzuki coupling approach. The conjugated polymer was highly soluble in common organic solvents such as NMP, THF, dichloromethane, chloroform, toluene, xylene, and benzene at room temperature. The polymer had high glass transition temperature at 191 C and Td10 at 434 C in nitrogen atmosphere. The pristine polymer exhibited the UV,vis maximum absorption at 355 nm and shifted to 420 nm after protonation. The emission of the polymer in THF solution changed from the blue region with maximum peak at 400 nm to the yellow region with maximum peak at 540 nm after protonated by HCl, and the intensity of emission depended on the concentration of acid. The polymer also showed electrochromic behavior under applied voltage. The emission color of the polymer film changed from blue (435 nm) to yellow (570 nm) when 2.5 V bias voltage was applied. The polymer also exhibited write-once and read-many-times (WORM) polymer memory effect with tristable states. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 991,1002, 2009 [source]


Living radical photopolymerization induced grafting on thiol,ene based substrates

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2005
Sirish K. Reddy
Abstract The formation of reactive substrates with iniferter-mediated living radical photopolymerization is a powerful technique for surface modification, which can readily be used to facilitate the incorporation of a variety of surface functionalities. In this research, the photopolymerization kinetics of novel bulk thiol,ene systems have been compared with those of typical acrylate and methacrylate systems when polymerized in the presence of the photoiniferter p -xylene bis(N,N -diethyl dithiocarbamate) (XDT). In the presence of XDT, the thiol,ene systems photopolymerize more quickly than the traditional acrylate and methacrylate systems by one to two orders of magnitude. Fourier transform infrared spectroscopy has been used to monitor the photografting kinetics of various monomers on dithiocarbamate-functionalized surfaces. Furthermore, this technique has been used to evaluate surface-initiation kinetics and to emphasize the influence of bulk substrate properties on grafting kinetics. Finally, photopatterning has been demonstrated on a dithiocarbamate-incorporated thiol,ene substrate with conventional photolithographic techniques. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2134,2144, 2005 [source]