Preventive measures benzene

Analytical methods have been developed to measure benzene levels in exhaled breath, blood, and various body tissues. The primary method of analyzing for benzene in exhaled breath, body fluids and tissues is gas chromatography (GC) coupled with either flame ionization detection (FID), photoionization detection (PID), or mass spectrometry (MS). Rigorous sample collection and preparation methods must be followed when analyzing for benzene to prevent contamination of the sample. A summary of commonly used methods of measuring benzene in biological samples is presented in Table 6-1. 

The variability in chemiluminescence from the photooxidation of solid polymer films prevented measurements of /3-values in solid media, where the results would be most pertinent to the general question of polymer stability. We might expect a close correspondence of /3-values to those determined in solution in this work, since the lifetimes of singlet oxygen in benzene and cyclohexane, which should bracket the properties of the polymers in this study, are nearly identical (22). 

For decades, benzene, classified carcinogenic first category, is no longer used as a solvent for paints, inks, glues, or varnishes. It retains a limited use for situations where this molecule is the basis, for example, of a manufacturing process for essential benzene-derived molecules. In many cases, it is impossible to simply delete the danger. So it will often need to implement effective risk prevention measures. 

Viscosity measurements were performed in THF solution, after substitution of benzene by THF, in order to prevent a possible aggregation of species in hydrocarbon solvents. 

Trithiadiazepine (12.1) is colorless, planar, and symmetrical, and has bond lengths intermediate between double and single as expected for a IOtt aromatic system the C—C bond length is 1.346 A. The benzo derivative (12.2) is also planar and symmetrical, but is bright yellow, and there is bond alternation in the benzene ring (see 12.2) akin to that found in naphthalene. Crystal discontinuities have prevented the accurate measurement of the structural details of 12.3, which is also colorless, but it is presumed to be planar. 

Benzene, administered intraperitoneally at 600 mg/kg in com oil, 2 times per day for 2 days to male C57BL/6J mice, caused a significant depression in the total number of nucleated bone marrow cells per femur, when measured on day 3 (Niculescu and Kalf 1995). Additional experiments with 7-day exposure revealed that there was an initial depression in erythroid cells on day 3 which remained constant lymphocytes exhibited a progressively depressive effect, and the numbers of intermediate and terminally differentiated granulocytes exhibited a progressive increase over the 7 days of exposure. Upon cessation of the benzene treatment, the bone marrow appeared to begin recovery, with the number of nucleated cells equal to control animals by day 7 after treatment ended. Concomitant administration of IL-la prevented the decrease in nucleated bone marrow cells, whereas IL-la administered after 2 days of benzene exposure significantly increased the rate of recovery of bone marrow cellularity. 

The electron temperature (Tg), electron density (ng) and electron energy distribution function for a plasma sustained in an argon/benzene mixture were measured by double and triple plasma-probe methods. Each probe was heated up to 1000 K with a sheathed heater, which was inserted into the probe, in order to prevent... 

The gas-phase tram-alkylation reaction was performed in an automated micro-flow apparatus containing a quartz fixed-bed reactor (i d. 10 mm) at lO Pa [16 vol% benzene (1, p.a., dried on molsieve), 3.2 vol% diethylbenzene (2, consisting of 25% ortho, 73% meta, 2% para isomers, dried on molsieve), N2 balance (50 mL/min), WHSV =1.5 h ] with 2.0 mL of the tube reactor filled with catalyst particles (500-850 pm sieve fraction, typically 1.4 g). Two separate saturators were connected to the inlet of the reactor for the supply of 1 and 2. The partial vapor pressure of 1 and 2 was controlled by adjusting the temperature of the saturator-condensers and the N2 flow rate. After equilibration for 30 min at the applied reaction temperatures (473 K and 673 K, heating rate 10 K/min) within a dry N2 flow (50 mL/min), benzene (1) and diethylbenzene (2) were passed throu the reactor. To prevent condensation of both reactants and products prior to GC analysis [Hewlet Packard 5710 A, column CP-sil 5CB capillary liquid-phase siloxane polymer (100% methyl) 25 m x 0.25 mm, 323 K, carrier gas N2, FID, sample-loop volume 1.01 pL], tubes were heat-traced (398 K). FID sensitivity factors and retention times were determined using ethene (99.5 %, dried over molsieve) and standard solutions of 1, 2, and ethylbenzene (3, 99%) in methanol (p.a.). The conversion of 2 was measured as a function of time [8]. 

A 3 1 ratio of triplet singlet yields is to be expected only if the spurs contain a sufficient number of recombining ions and any exciting electrons remain close to positive ions (37). A serious problem which remains is the reason for higher triplet yields measured by isomerization methods compared with pulse radiolysis—e.g., 2.8 is the estimated yield in benzene-biacetyl solution (13). The difference could arise from quenching of excited states during the pulse, preventing their observation. Nanosecond pulse experiments may resolve the discrepancy. 

An extensive but unfortunately, as yet, unpublished study by Yamaoka (28) was concerned with the mode of orientation of several polypeptides in varied solvents under the influence of a rectangular voltage pulse. While measurements could be made in most organic solvents, he was unable to obtain steady-state values for the birefringence of PBLG dissolved in benzene and dioxane, except at low concentrations in dioxane. Extremely long rise times were observed in these solvents, and the 1.4-millisecond limit on his pulse width prevented establishment of equilibrium. Yamaoka showed by means of optical rotatory dispersion that PBLG assumes a helical conformation in benzene. 

How far carbocation chemistry has evolved from the old solvolysis days is demonstrated by two recent stmcture determinations the IR spectrum of the nonclassical CHs cation has been measured by solvating this unusual species with molecular hydrogen in the gas phase. This slows down the ultrafast fluxional process which so far prevented the recording of vibrational spectra. The cluster ions CH5" (H2)n (n = 1, 2, 3), after mass selection by an ion trap, were then subjected to IR laser spectroscopy/quadrupol mass spectrometry which ultimately yielded the IR absorption. [40] And the benzene cation, formed by removal of one electron from the parent hydrocarbon was shown to possess Deh symmetry by rotation resolved ZEKE-photoelec-tron spectroscopy (Zero Tinetic Energy-PES). [41]... 

The extreme solvent sensitivity of the exciplex fluorescence is very interesting. Fullerene-amine exciplex emissions observed in saturated hydrocarbon solvents are absent in solvents such as benzene and toluene (27,84,88,101), which has been explained in terms of solvent polarizability effects [101]. However, there has also been an explanation [84] that the formation of exciplexes in a solvent such as benzene is hindered by specific solute-solvent interactions that result in complexation between the fullerene and solvent molecules. The two explanations are fundamentally different. In the former, the exciplex state is effectively quenched through a radiationless decay pathway facilitated by a stronger dielectric field of the solvent. However, the latter assumes that the ground state fiillerene-solvent complexation prevents the formation of fullerene-donor exciplexes. In order to understand whether the extreme solvent sensitivity is solvent specific (limited to benzene, toluene, and other aromatic solvents) or solvent property specific (solvent polarity and polarizability), fluorescence spectra of C70-DEA were measured systematically in mixtures of hexane and a polar solvent (acetone, THF, or ethanol) with volume fraction up to 10% [101]. The results are consistent with the explanation of solvent polarity and polarizability effects. 

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