Dichlorobenzene Isomers Research Articles

Gas chromatographic–mass spectrometric analysis of dichlorobenzene isomers in human blood with headspace solid-phase microextraction

Headspace solid-phase microextraction (HS-SPME) was utilized for the determination of three dichlorobenzene isomers (DCBs) in human blood. In the headspace at 30°C, DCBs were absorbed for 15 min by a 100-μm polydimethylsiloxane (PDMS) fiber. They were then analyzed by capillary column gas chromatography–mass spectrometry (GC–MS). By setting the initial column oven temperature at 20°C, the three isomers were resolved at the baseline level. p-Xylene-d 10 was used as the internal standard (I.S.). For quantitation, the molecular ion at m/ z 146 for each isomer and the molecular ion at m/ z 116 for I.S. were selected. For day-to-day precision, relative standard deviations in the range 3.2–10.7% were found at blood concentrations of 1.0 and 10 μg/ml. Each compound was detectable at a level of at least 0.02 μg per 1 g of whole blood (by full mass scanning). HS-SPME–GC–MS, when performed at relatively low temperatures, was found to be feasible in toxicological laboratories. Using this method, the plasma levels of one patient who had drunk a pesticide-like material were measured.

Degradation of chlorobenzenes at nanomolar concentrations by Burkholderia sp. strain PS14 in liquid cultures and in soil.

The utilization of 1,2,4,5-tetrachloro-, 1,2,4-trichloro-, the three isomeric dichlorobenzenes and fructose as the sole carbon and energy sources at nanomolar concentrations was studied in batch experiments with Burkholderia sp. strain PS14. In liquid culture, all chlorobenzenes were metabolized within 1 h from their initial concentration of 500 nM to below their detection limits of 0.5 nM for 1,2,4,5-tetrachloro- and 1,2,4-trichlorobenzene and 7.5 nM for the three dichlorobenzene isomers, with 63% mineralization of the tetra- and trichloroisomers. Fructose at the same initial concentration was, in contrast, metabolized over a 4-h incubation period down to a residual concentration of approximately 125 nM with 38% mineralization during this time. In soil microcosms, Burkholderia sp. strain PS14 metabolized tetrachlorobenzene present at 64.8 ppb and trichlorobenzene present at 54.4 ppb over a 72-h incubation period to below the detection limits of 0.108 and 0.09 ppb, respectively, with approximately 80% mineralization. A high sorptive capacity of Burkholderia sp. strain PS14 for 1,2,4, 5-tetrachlorobenzene was found at very low cell density. The results demonstrate that Burkholderia sp. strain PS14 exhibits a very high affinity for chlorobenzenes at nanomolar concentrations.

Effect of contaminant and organic matter bioavailability on the microbial dehalogenation of sediment-bound chlorobenzenes

The extent of reductive dechlorination occurring in contaminated, estuarine sediments was investigated. Contaminant and organic matter bioavailability and their effect on the reductive dechlorination of sediment-bound chlorobenzenes was the main focus of the work presented here. Sediment and water samples were collected from a contaminated estuarine system with more than 40 yr of contamination history. Hexachlorobenzene and other chlorinated benzene congeners were the predominant chlorinated compounds encountered. Anaerobic batch assays revealed that the sediment natural organic matter is recalcitrant and unable to support active microbial growth. However, sediment nutrients (e.g. N, P) were available in sufficient quantities to support an accelerated microbial growth. Static microcosms were constructed with sediment and water from the study site. The sediment microbial consortia were able to reductively dechlorinate the sediment-bound polychlorinated benzene congeners, primarily to dichlorobenzene isomers. The first-order rate constant for hexachlorobenzene depletion ( k obs) ranged from 2.2 × 10 −3 to 2.9 × 10 −3 d −1, the higher value being achieved in microcosms supplemented with dextrin. These rates were about two orders of magnitude lower than those observed with the same sediment-derived, mixed dechlorinating microbial consortium in liquid cultures supplemented with freshly added hexachlorobenzene. The extent of hexachlorobenzene removal over a long incubation time (more than 480 d) was only 43%, most of which occurred during the first 200 d of incubation. Both the recalcitrant nature of the sediment organic matter and the strong partitioning of the chlorinated compounds were responsible for the low rate and extent of contaminant transformation. When frequent additions of a degradable organic carbon source and ground sediment were used, an increased rate and extent of reductive dechlorination of the sediment-bound contaminants were observed (e.g. 95% hexachlorobenzene biotransformation within 205 d of incubation; k obs = 2.1 × 10 −2 d −1).

Isomer-Specific Acute Toxicity and Cell Proliferation in Livers of B6C3F1 Mice Exposed to Dichlorobenzene

The acute hepatotoxicity of isomers of dichlorobenzene (o-,m-, andp-DCB) was compared in livers of male B6C3F1 mice at different time points after a single intragastric administration. The highest doses ofo-,m-, andp-DCB administered, 300, 300, and 1800 mg/kg, respectively, are below the lethal range. Acute hepatic injury was assessed by serum alanine aminotransferase (ALT) activity and hepatic histology. Hepatocyte replication was estimated by means of immunohistochemical demonstration of BrdU-labeled cells. Botho-DCB andm-DCB at a dose of 300 mg/kg produced significant elevations of liver weight and ALT activity as well as extensive liver cell necrosis. In contrast,p-DCB at a highest dose of 1800 mg/kg induced slight hepatocyte injury. Dose–response studies indicated that the rank order for acute hepatotoxicity of the isomers wasm-DCB >o-DCB much greater thanp-DCB. However,p-DCB induced hepatocyte cell proliferation in spite of the lack of manifest hepatotoxicity. In contrast, increases of cell proliferation due too- orm-DCB exposure occurred only after dosages that caused hepatic injury. These data suggest the hepatocyte proliferation induced byo- orm-DCB is compensatory regeneration while that induced byp-DCB is a response to mitogenic stimulation.

Dichlorobenzene Ionization Energies

Electron propagator calculations on the lowest 14 vertical ionization energies of the para, meta, and ortho isomers of dichlorobenzene are performed using the OVGF and P3 approximations, where Feynman−Dyson amplitudes are equivalent to canonical molecular orbitals. Cl p orbitals destabilize the e1g set of benzene to produce the molecular orbitals associated with the two lowest ionization energies. Holes corresponding to four higher final states have mostly Cl 3p character. The remaining molecular orbitals strongly resemble their benzene counterparts, but significant Cl admixtures are present in most cases. Previous assignments for m-dichlorobenzene are confirmed, and remaining uncertainties in the ortho and para spectra are resolved. Basis sets with up to 304 contracted functions are used. Agreement with experimental ionization energies is close.

Determination of Nanogram per Liter Concentrations of Volatile Organic Compounds in Water by Capillary Gas Chromatography and Selected Ion Monitoring Mass Spectrometry and Its Use To Define Groundwater Flow Directions in Edwards Aquifer, Texas

A method has been developed to measure nanogram per liter amounts of selected volatile organic compounds (VOCs) including dichlorodifluoromethane, trichlorofluoromethane, cis-1,2-dichloroethene, trichloroethene, tetrachloroethene, and the isomers of dichlorobenzene in water. The method uses purge-and-trap techniques on a 100 mL sample, gas chromatography with a megabore capillary column, and electron impact, selected ion monitoring mass spectrometry. Minimum detection levels for these compounds ranged from 1 to 4 ng/L in water. Recoveries from organic-free distilled water and natural groundwater ranged from 70.5% for dichlorodifluoromethane to 107.8% for 1,4-dichlorobenzene. Precision was generally best for cis-1,2-dichloroethene, tetrachloroethene, and the dichlorobenzene isomers and worst for dichlorodifluoromethane and trichlorofluoromethane. Blank data indicated persistent, trace-level introduction of dichlorodifluoromethane, 1,4-dichlorobenzene, and tetrachloroethene to samples during storage and shipment at concentrations less than the method reporting limits. The largest concentrations of the selected VOCs in 27 water samples from the Edwards aquifer near San Antonio, TX, were from confined-zone wells near an abandoned landfill. The results defined a zone of water with no detectable VOCs in nearly all of the aquifer west of San Antonio and from part of the confined zone beneath San Antonio.

Alkylation of dichlorobenzene isomers by olefins on zeolites Y and pentasil

Catalytic alkylation of dichlorobenzene isomers by ethylene and propylene on zeolite catalysts has been studied. It has been determined that using catalysts based on zeolite Y makes it possible to change the ratio of 1-alkyldichlorobenzenes formed within a wide range by varying the acidic properties of the catalysts.

Mechanistic study of hydrogen/deuterium exchange between [M − 1] − ions of chlorinated benzenes and D 2O or ND 3

Low-energy collisions between [M ☆- 1] − ions derived from the three isomers of dichlorobenzene and deuterated water and ammonia are found to produce distinctive hydrogen/deuterium (H/D) exchange reaction product patterns. The predominant products observed for p-, m-, and o-dichlorobenzene are 1, 2, and 3 sequential deuterium exchanges, respectively. The reactivity is substantially higher for D 2O than ND 3. We postulate a mechanism that involves the formation of a five-membered-ring intermediate. The intermediate is thought to be initiated by the attack of ND 3 or D 2O at the localized negative charge site on the aromatic ring. A successful exchange is followed by the relocation of the charge site of the adjacent carbon. Ion products with higher degrees of deuterium substitution than the expected predominant products of their corresponding isomers are believed to be the results of isomerization of the reactant ions occurring in the ion source. The proposed mechanism fully explains the observed product spectra derived from all the isomers of chlorinated benzenes. The trends for the formation of various H/D exchange products represented by the simulated product-time plots based on the proposed mechanism compare well with the similar trends obtained from the experimental product-pressure plots. The reaction is useful for the mass spectrometric differentiation of chlorobenzene isomers.

Chemical fate and transport in a domestic septic system: Site description and attenuation of dichlorobenzene

AbstractThe mobility and attenuation of dichlorobenzene (DCB) in a septic system groundwater contaminant plume with a very detailed monitoring network was evaluated by conducting a tracer experiment in which 450 ml of a plumbing line cleaner containing DCB and 1 kg NaBr were injected into the septic system. DCB concentrations of up to 3,460 μg/L were observed in the septic tank effluent, up to 650 μg/L in the unsaturated zone 0.45 m below the tile bed, and up to 13 μg/L at the water table at 2 m depth. Peak DCB concentrations arrived at the water table after 57 d at a source‐normalized concentration of 0.02, whereas peak Br− concentrations arrived at the water table after only 10 d at a normalized concentration of 0.61, thus demonstrating DCB attenuation and retardation during migration through the aerobic unsaturated zone at this site. Model simulations of DCB breakthrough at the water table provided an adequate fit with the field data when a retardation factor of 6.5 and decay half‐life of 15 d were used. Evidence for biodegradation of DCB was provided by the occurrence of a 7‐d lag (biota acclimation period), after which increased attenuation of DCB was observed in the unsaturated zone and by the preferential attenuation of two of the three isomers of DCB. Vigorous biodegradation of trace volatile organic compounds such as halogenated and substituted benzenes was indicated in the unsaturated zone below this septic system.

Gas phase substitution of halobenzenes by methylamine and dimethylamine via radical cations

The reactions of the radical cations of the halobenzenes C 6H 5X + (X = Cl, Br, I), the isomeric dichlorobenzenes and the isomeric chloroiodobenzenes with CH 3NH 2 as well as the reactions of the radical cations CH 3NH 2 + and (CH 3) 2NH + with the above neutral halobenzenes were studied by Fourier transform ion cyclotron resonance spectrometry. In all cases the substitution of a halogen substituent by R 2NH + (R = H, CH 3) was observed besides charge exchange. The substitution of halobenzene radical cation by CH 3NH 2 is always fast (the reaction efficiency (eff subst) being greater than 28%) compared to the reaction with NH 3 studied before, but exhibits principally the same dependence on the nature and position of the halogen substituent as the latter reaction. The substitution of neutral halobenzenes, where the ionization energy of the halobenzene is greater than the ionization energy of methylamine, by CH 3NH 2 + is also fast (eff subst > 50%) and is not much influenced by the structure of the halobenzene. In contrast, the rate of substitution of all halobenzenes by (CH 3) 2NH + is small (eff subst < 14%), increases with the halogen lost in the series Cl < Br < I, and exhibits a distinct orientation effect for dihalobenzenes, the meta isomer being least reactive. These experimental results are discussed using thermochemical data from the literature and the curve crossing model of Shaik and Pross. The results are consistently rationalized for the reaction of ionized halobenzenes with neutral amines as well as the reaction of neutral halobenzenes with ionized amines by a mechanism involving addition to the aromatic system, rearrangement of the intermediate distonic ion to an ipso-substituted isomer, and dissociation of the intermediate by loss of halogen. However, the rate-determining step of this mechanism depends on the substrates involved, and this structural dependence of the reactions can be understood by the curve crossing model.

In- Vitro Hepatotoxicity of Three Dichlorobenzene Isomers in Human Liver Slices

1 The cytotoxicity of dichlorobenzenes in cultured rat liver slices has previously been shown to be strain specific and biotransformation related. 2 In order to extrapolate animal models to humans, the dichlorobenzenes were incubated with human liver slices to try to clarify their hepatotoxic potential in man. 3 The degree of hepatotoxicity observed with the dichlorobenzenes depended on whether Waymouth's or Krebs-Henseleit was used as the incubation medium. 4 All three dichlorobenzenes (1 mM) produced no significant differences from control when incubated in Waymouth's medium. However, in the Krebs-Henseleit buffer there was a substantial increase in cytotoxicity. 5 In both incubation mediums the dichlorobenzene isomers exhibited the following rank order 1,3-DCB greater than 1,2-DCB greater than 1,4-DCB. 6 1,2-dichlorobenzene hepatotoxicity was blocked by metyrapone, 1,3-dichlorobenzene toxicity was blocked by SKF 525-A and neither one of these inhibitors could block the 1,4-dichlorobenzene cytotoxicity. 7 The use of human liver tissues to evaluate potential toxicants merits consideration since the hepatotoxicity of xenobiotics and drugs in man is the ultimate question.

The acute hepatotoxicity of the isomers of dichlorobenzene in Fischer-344 and Sprague-Dawley rats: Isomer-specific and strain-specific differential toxicity

The acute hepatotoxicity of the three isomers of dichlorobenzene (DCB) was evaluated in male Fischer-344 (F344) rats at various times following ip administration. Plasma alanine aminotransferase (ALT) activity, measured in F344 rats 24 hr postexposure, was dramatically elevated following doses of 1.8–5.4 mmol/kg of o-DCB. Conversely, equimolar doses of p-DCB produced no such toxicity, while m-DCB produced intermediate hepatic injury at or above doses of 2.7 mmol/kg. Histopathological changes in livers from treated animals qualitatively reflected elevations in 24-hr plasma ALT activity (time to maximal elevation). Phenobarbital pretreatment potentiated the acute hepatotoxicity of o- and m-DCB, but did not affect the toxicity of p-DCB. Likewise, SKF-525A pretreatment inhibited the hepatotoxicity of o-DCB. Equimolar doses of o- and m-DCB produced approximately equivalent depletion of intrahepatic glutathione, while p-DCB had no effect on hepatic GSH. Furthermore, prior depletion of hepatic glutathione by pretreatment with phorone markedly potentiated the hepatotoxicity of o- and m-DCB, while increasing the toxicity of p-DCB to a far lesser degree. The differential hepatotoxicity of the o- and m-DCB does not appear to be explained adequately by differences in their hepatic distribution or in in vivo covalent binding to hepatic proteins. Interestingly, male Sprague-Dawley (SD) rats are relatively refractive to the acute hepatotoxicity of o-DCB following ip administration of 1.8 and 5.4 mmol/kg. The combination of these dramatic differences (structure-activity and animals strains) should be useful in elucidating key events involved in the hepatotoxicity caused by these compounds.

Degradation of 1,2,4-Trichloro- and 1,2,4,5-Tetrachlorobenzene by Pseudomonas Strains

Two Pseudomonas sp. strains, capable of growth on chlorinated benzenes as the sole source of carbon and energy, were isolated by selective enrichment from soil samples of an industrial waste deposit. Strain PS12 grew on monochlorobenzene, all three isomeric dichlorobenzenes, and 1,2,4-trichlorobenzene (1,2,4-TCB). Strain PS14 additionally used 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB). During growth on these compounds both strains released stoichiometric amounts of chloride ions. The first steps of the catabolism of 1,2,4-TCB and 1,2,4,5-TeCB proceeded via dioxygenation of the aromatic nuclei and furnished 3,4,6-trichlorocatechol. The intermediary cis-3,4,6-trichloro-1,2-dihydroxycyclohexa-3,5-diene (TCB dihydrodiol) formed from 1,2,4-TCB was rearomatized by an NAD-dependent dihydrodiol dehydrogenase activity, while in the case of 1,2,4,5-TeCB oxidation the catechol was obviously produced by spontaneous elimination of hydrogen chloride from the initially formed 1,3,4,6-tetrachloro-1,2-dihydroxycyclohexa-3,5-diene. Subsequent ortho cleavage was catalyzed by a type II catechol 1,2-dioxygenase producing the corresponding 2,3,5-trichloromuconate which was channeled into the tricarboxylic acid pathway via an ordinary degradation sequence, which in the present case included 2-chloro-3-oxoadipate. From the structure-related compound 2,4,5-trichloronitrobenzene the nitro group was released as nitrite, leaving the above metabolite as 3,4,6-trichlorocatechol. Enzyme activities for the oxidation of chlorobenzenes and halogenated metabolites were induced by both strains during growth on these haloaromatics and, to a considerable extent, during growth of strain PS12 on acetate.

Precision-Cut Rat Liver Slices in Dynamic Organ Culture for Structure-Toxicity Studies

We describe a novel in vitro mammalian liver system, which simplifies both metabolism and hepatotoxicity studies in a multitude of species. This system is based on mechanical cutting of slices with high precision and culture of such slices under dynamic organ culture conditions. This system permits study of intoxication or metabolism for many hours to days and is suitable for integrative biochemical assays as well as histological and morphological evaluation. We report the toxicity exhibited by the isomeric dichlorobenzenes, which in Sprague-Dawley rat liver slices is M&gt;O&gt;P. We also compared a series of bromobenzene analogs, which in Sprague-Dawley rat liver slices are toxic in the following sequence DBB &gt; BB &gt; BBN &gt; BA &gt; BBT &gt; BT. The toxicity of medium chain length branched-chain fatty acids related to valproic acid also was evaluated in this system. Results show that toxicity increased with chain length in α-methyl fatty acids and depended on the location of the carboxyl group in branched-chain octanoic acids. These examples serve to illustrate the utility of precision-cut rat liver slices in dynamic organ culture for structure—toxicity studies.

Photochemistry of chlorobenzene derivatives in solution: role of the substituent and its position in photoreduction

Quantum yields φ have been determined for the formation at λ = 254 nm of hydrogen chloride and the product of photoreduction (ClC 6H 4R → C 6H 5R) during the photolysis of chlorobenzene derivatives with chlorine, fluorine, CH 3, OCH 3, CF 3, CH 2OH, CN and CH 2CN substituents in the ortho, meta and para positions in solutions of aliphatic hydrocarbons. The φ values determined indicate that ortho isomers of the compounds studied are distinguished by considerably higher photoreactivity than the other isomers. However, when compared with chlorobenzene, ortho isomers of dichlorobenzene and fluorochlorobenzene are more photoreactive and ortho isomers of chlorobenzonitrile, chlorobenzylcyanide and chloro(trifluoromethyl)benzene are less photoreactive. The photoreactivities of the other two isomers (meta and para) of all the compounds investigated are lower than that of chlorobenzene. Experiments carried out in the presence of sensitizers and quenchers provided data on the contribution of singlet (S 1) and triplet (T 1) states to the photolysis of some of the compounds studied.

Ortho-, meta-, and para-dichlorobenzene.

Ortho-, meta-, and para-dichlorobenzene (1,2-dichlorobenzene, 1,3-dichloro-benzene, 1,4-dichlorobenzene, respectively) are also called o-DCB, m-DCB, and p-DCB. Historically, p-DCB is also known as PDB. The first is used as a solvent, chemical intermediate, and deodorizer; the second has no documented use; and the third is used as a deodorizer and insecticide. For the structures and properties of ortho-, meta-, and para-dichlorobenzene, see Tables 1, 2, and 3, respectively.There are no natural sources for the three isomers of dichlorobenzene (DCB). Production of the DCB isomers in 1981 was 11 million lb (4.99 million kg) for the ortho-isomer and 15 million (6.8 million kg) for the para-isomer. Production levels for the meta-isomer were not reported but are believed to be small.

Degradation of low concentrations of dichlorobenzenes and 1,2,4-trichlorobenzene byPseudomonassp. strain P51 in nonsterile soil columns

A newly isolated Pseudomonas species, strain P51, growing aerobically on all dichlorobenzene isomers and on 1,2,4-trichlorobenzene as sole carbon and energy sources was tested for its ability to mineralize these components also in a non-sterile soil environment. Untreated sand from the river Rhine in which none of the dichloro- and trichlorobenzenes were degraded was placed in a percolation column and inoculated with Pseudomonas sp. strain P51. The column was fed continuously with synthetic river water containing the chlorinated compounds at concentrations between 10 μg/1 and 1 mg/1. The inoculated microorganisms were able to degrade the chlorinated benzenes and survived for at least 60 days in the column. For each compound a specific threshold concentration was observed below which no further degradation took place, and which was independent of the initial concentration. These threshold were 6 ± 4 μg/1 for 1,2-dichlorobenzene, 20 ± 5 μg/1 for 1,2,4-trichlorobenzene and more than 20 μg/1 for the 1,3- and 1,4-isomers. Repeated inoculation of the column with strain P51 did not affect this minimal concentration. In noninoculated soil columns the native microbial population adapted to degrade 1,2-dichlorobenzene after a long lag phase, and reduced it from 25 μg/1 to a threshold concentration of 0.1 μg/1.

The bone marrow clastogenicity of eight halogenated benzenes in male NMRI mice.

Eight widely used halogenated benzenes, including bromobenzene (BB), chlorobenzene (CB), three isomers of dichlorobenzene (DCB) and three isomers of trichlorobenzene (TCB) were tested for acute toxicity (LD50) and clastogenicity in 8-week-old NMRI mice by intraperitoneal administration. Four doses of each chemical (up to 70% of LD50) were tested for clastogenic activity. Each compound was administered in two equal doses, 24 h apart. Increased formation of micronucleated polychromatic erythrocytes, observed in femoral bone marrow, 30 h after the first injection, was considered to be due to the clastogenic activity of the test compound. All the halogenated benzenes tested were found to be clastogenic (P less than 0.01). The highest clastogenic activities were induced by m-DCB and BB. Among the three isomers of DCB, m-DCB significantly (P less than 0.05) induced more micronuclei than o-DCB or p-DCB. No significant differences were found between the clastogenic activities of TCB isomers.

Effect of polarity on the adsorption of dichlorobenzene isomers

The influence of reference vapor polarity on the characterization of microporous carbon adsorbents using the Dubinin equations was investigated. Polarity may be an important parameter for reference vapor selection due to the influence of electrostatic forces on the adsorption of polar vapors. Adsorbate polarity was investigated by evaluating the adsorption isotherms and characteristic curves for the three isomers of dichlorobenzene and the heats of adsorption for the two liquid isomers. The three isomers are very similar in terms of molecular weight, vapor pressure, density, and electronic polarizations. The major difference is the range of dipole moments: 1,2-dichlorobenzene, 2.50 D; 1,3-dichlorobenzene, 1.72 D; and 1,4-dichlorobenzene, 0.00 D. If adsorbate polarity has a major influence on adsorption, the three characteristic curves should have different slopes. The slopes of the three curves were not statistically different at the 95% level, and no difference in the heats of adsorption was observed. It was concluded, therefore, that electrostatic forces do not have a major influence on vapor adsorption when adsorbate polarities are between 0 and 2.50 D. Therefore, a single reference vapor may be adequate for characterization of microporous carbon adsorbents.

New liquid crystalline stationary phases for gas chromatography of positional and geometrical isomers having similar volatilities

New liquid crystalline compounds of the type 2-methyl-4′-R-4-( p-methoxycinnamoyloxy)azobenzene, where R = methoxy, ethoxy, ethyl or n-butyl, were synthesized. Their properties as stationary phases for the gas chromatographic separation of positional isomers of xylene, dichlorobenzene, methoxynaphthalene and geometrical isomers of insect sex pheromones of similar volatilities have been investigated. The effect of temperature on the separation ability of the liquid crystalline compounds was studied. Large separation factors, α, for isomers were obtained on a column in its supercooled nematic state. The separation of insect sex pheromones was found to depend on the structure of the liquid crystalline compound used as stationary phase rather than on its nematic range.