Search results for "Xylene"
showing 10 items of 58 documents
Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of S N Ar Chemistry
2020
The reactivity of the electron-rich anionic Al(I) ('aluminyl') compound K 2 [(NON)Al] 2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di- tert -butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C-H activation chemistry with n -butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical S N Ar chemistry, which implies the destabilization of transition states featuring electron-donating groups in either the ortho or the para positions. In the cases of tolu…
Biofiltration of airborne VOCs with green wall systems : microbial and chemical dynamics
2018
Botanical air filtration is a promising technology for reducing indoor air contaminants, but the underlying mechanisms need better understanding. Here, we made a set of chamber fumigation experiments of up to 16 weeks of duration, to study the filtration efficiencies for seven volatile organic compounds (VOCs; decane, toluene, 2-ethylhexanol, α-pinene, octane, benzene, and xylene) and to monitor microbial dynamics in simulated green wall systems. Biofiltration functioned on sub-ppm VOC levels without concentration-dependence. Airflow through the growth medium was needed for efficient removal of chemically diverse VOCs, and the use of optimized commercial growth medium further improved the e…
The individual contribution of starter and non-starter lactic acid bacteria to the volatile organic compound composition of Caciocavallo Palermitano …
2017
Abstract The contribution of two starter ( Lactobacillus delbrueckii and Streptococcus thermophilus ) and nine non-starter ( Enterococcus casselliflavus , Enterococcus faecalis , Enterococcus durans , Enterococcus gallinarum , Lactobacillus casei , Lactobacillus paracasei , Lactobacillus rhamnosus , Pediococcus acidilactici and Pediococcus pentosaceus ) species of lactic acid bacteria (LAB) to the volatile organic compounds (VOCs) of Caciocavallo Palermitano cheese was investigated. The strains used in this study were isolated during the production/ripening of the stretched cheese and tested in a cheese-based medium (CBM). The fermented substrates were analyzed for the growth of the single …
Vapor−Liquid Equilibria for the Binary Systems Isobutanol with m-Xylene, o-Xylene and p-Xylene at 101.3 kPa
1999
Vapor−liquid equilibria were measured for binary systems of isobutanol with m-xylene, o-xylene, and p-xylene at 101.3 kPa using a recirculating still. The accuracy of experimental measurements was ±0.1 K in temperature, ±0.01 kPa in pressure, and ±0.001 in mole fraction. The results were determined to be thermodynamically consistent according to the point-to-point consistency and Wisniak tests. All the systems show moderate positive deviations from ideality. The data were correlated with five liquid-phase activity coefficient models (Margules, Van Laar, Wilson, NRTL, UNIQUAC).
Adsorption Properties of Nax and Bax Zeolites: Correlation between Structural and Thermodynamic Results on Para- and Meta-xylene Adsorption
1996
A comparison is made between NaX and BaX adsorption properties starting from crystallographic data and thermodynamic measurements. Adsorption isotherms and differential adsorption heats of pure para- and meta-xylenes in NaX and BaX zeolites are interpreted in the light of crystallographic results.
Headspace–mass spectrometry determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers in soil samples using chemometrics
2007
A simple and fast method has been developed for the determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers (BTEX) in soils. Samples were introduced in 10 mL standard glass vials of a headspace (HS) autosampler together with 150 microL of 2,6,10,14-tetramethylpentadecane, heated at 90 degrees C for 10 min and introduced in the mass spectrometer by using a transfer line heated at 250 degrees C as interface. The volatile fraction of samples was directly introduced into the source of the mass spectrometer which was scanned from m/z 75 to 110. A partial least squares (PLS) multivariate calibration approach based on a classical 3(3) calibration model was build with m…
Outdoor, indoor and personal distribution of BTEX in pregnant women from two areas in Spain - Preliminary results from the INMA project
2010
Volatile organic compounds (VOCs), which are habitually found in both outdoor and indoor environments, may represent a significant health risk. In this context, pregnancy is a critical period since foetuses are more vulnerable than adults to exposure to toxic compounds. The objective of this study is to present the preliminary results of a series of measurements of outdoor (O), indoor (I) and personal exposure (P) to benzene, toluene, ethylbenzene, o-xylene and m,p-xylene (BTEX) in 107 pregnant women from two areas in Spain, namely Valencia and Sabadell. BTEX samplers were installed for 48 hours both inside and outside of the women’s homes, along with personal samplers. In addition, the tes…
On the mechanism of catalytic isomerization of xylenes. Molecular orbital studies
1979
Abstract On the basis of CNDO/2 molecular orbital calculations, we postulate the following detailed mechanism for the catalytic isomerization of xylenes which explains the initial product distributions and also our previous finding that the reaction is intramolecular: (i) adsorption of xylene on a surface acid site to form a Wheland-type complex; (ii) disrotatory cyclization of the protonated species into a bicyclo[3, 1, 0]hexenyl complex; (iii) migration of the methylene bridge to a new side of the pentagonal ring; (iv) change of the new bicyclic species back into the corresponding Wheland-type complex; (v) desorption of the xylene isomer from the surface of the catalyst. The overall rate …
Chemical composition of the essential oils of Centaurea formanekii and Centaurea orphanidea ssp. thessala, two Centaurea species growing wild in Gree…
2012
The volatile constituents of the aerial parts of Centaurea formanekii Halacsy and the aerial parts, capitula and roots of C. orphanidea Heldr. & Sart. ex Boiss. ssp. thessala (Hausskn.) Dostál from Greece were extracted by hydrodistillation and analyzed. The main components in C. formanekii were hexadecanoic acid (13.6%), δ-elemene (9.1%), and spathulenol (6.9%). The main components in C. orphanidea ssp. thessala were γ-elemene (26.1%) and caryophyllene oxide (13.2%) in the aerial parts, hexadecanoic acid (33.5%) and heptacosane (6.3%) in the capitula, and hexadecanoic acid methyl ester (22.0%) and α-chamigrene (14.0%) in the roots. The chemotaxonomic significance with respect to other …
Influence of layer structure preservation on the catalytic properties of the pillared zeolite MCM-36
2010
MCM-36 is a catalytically active material made by swelling and subsequent pillaring of a layered zeolite precursor, MCM-22(P). However, the swelling procedures lead to significant destruction of layer structure and alteration of framework silicon/aluminum (Si/Al) ratio, which are likely to influence the acidity and catalytic activity of the final materials. We report a milder swelling and pillaring process to prevent such structural destruction. The resulting pillared materials show higher crystallinity and improved retention of the zeolitic layer structure when compared to the ones prepared by the previously reported methods involving more aggressive treatments. Implications of such struct…