Simultaneous conversion of CHClF(2) and CH(3)Br to CH(2)CF(2)

Gas phase reaction of CHClF(2) with CH(3)Br in an alumina tube reactor at 773-1123 K as a function of various input ratios of CH(3)Br to CHClF(2) is presented. The major products detected include C(2)F(4), CH(2)CF(2), and CH(4). Minor products include CH(3)Cl, CHF(3), C(2)H(4), C(2)H(2), CH(2)CF-CF(3), and C(2)H(3)F. The reaction produces a high yield of CH(2)CF(2) (53% based on CHClF(2) feed) at 1123 K and an input molar ratio of CH(3)Br to CHClF(2) of 1.8, suggesting that the reaction potentially can be developed as a process to convert two ozone depleting substances (CHClF(2) and CH(3)Br) to a highly valuable chemical, CH(2)CF(2). The reaction of CHClF(2) with CH(3)Cl and CH(3)I was also investigated under similar reaction conditions, to assist in understanding the reaction chemistry involved in the reaction of CHClF(2) with CH(3)Br.     

Photolysis of 2-(2-furyl)benzimidazole (Fuberidazole)

The photooxidatior. of 2-(4-thiazolyl)-1H-benzimidazole (Thia=bendazole (1) in methanol in presence and absence of a photo=sensitizer (methylene blue), is investigated. Dimethyl oxalate, thiazole-4-(N-carbomethoxy)-carboxamide (6), methyl benzimida=zole-2-carboxylate (7), benzimidazole-2-carboxamide (8), and benzimidazole (9), were the main products of the photolysis. Some reaction mechanisms are discussed.     

Atmospheric chemistry of HFE-7000 (CF(3)CF (2)CF (2)OCH (3)) and 2,2,3,3,4,4,4-heptafluoro-1-butanol (CF (3)CF (2)CF (2)CH (2)OH): kinetic rate coefficients and temperature dependence of reactions with chlorine atoms

Background, aim, and scope  The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF₃CF₂CF₂OCH₃) (1) and its isomer CF₃CF₂CF₂CH₂OH (2). Materials and methods  Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K for reactions of HFE-7000 and CF₃CF₂CF₂CH₂OH, respectively. Results  The measured room temperature rate constants were k(Cl+CF₃CF₂CF₂OCH₃) = (1.24 ± 0.28) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹and k(Cl+CF₃CF₂CF₂CH₂OH) = (8.35 ± 1.63) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ (errors are 2σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k ₁(266–333 K) = (6.1 ± 3.8) × 10⁻¹³exp[−(445 ± 186)/T] cm³ molecule⁻¹ s⁻¹ and k ₂(298–353 K) = (1.9 ± 0.7) × 10⁻¹²exp[−(244 ± 125)/T] cm³ molecule⁻¹ s⁻¹ (errors are 2σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2σ) were obtained for CF₃CF₂CF₂OCH₃ and CF₃CF₂CF₂CH₂OH, respectively. Discussion  The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into account the error limits. Comparing the obtained results at room temperature, k ₁ and k ₂, HFE-7000 is significantly less reactive than its isomer C₃F₇CH₂OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF₂– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties for a given application by changing the number of –CF₂– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C₃H₇CH₂OH, respectively. Conclusions  The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the marine boundary layer, τ _Cl values as low as 2.5 and 0.4 years for HFE-7000 and C₃H₇CH₂OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes under such conditions may constitute a relevant sink. In the case of CF₃CF₂CF₂OCH₃, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would result in underestimations of lifetimes and GWPs. Recommendations and perspectives  The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution is still required.     

Metabolism of 2-chloro-N-isopropylacetanilide (propachlor) in the rat.

Eleven urinary metabolites from [14C]propachlor were either identified or characterized by mass spectrometry. Those identified were 2-[S-(N-acetyl)cysteinyl]-N-isopropylacetanilide, 2-(methylsulfonyl)-acetanilide, 4'-hydroxy-2-(methylsulfonyl)-acetanilide, and 4'-hydroxyacetanilide. Those characterized were N-(1-hydroxyisopropyl)-2-(methylsulfonyl) acetanilide and its glucuronide, the glucuronides of 4'-hydroxy-N-isopropyl-2-(methylsulfonyl)acetanilide, N-(1-hydroxyisopropyl) aniline, 4'-hydroxy-2-(methylsulfonyl)acetanilide, and either N-(1-hydroxy-isopropyl) acetanilide or 2-hydroxy-N-isopropylacetanilide.     

(M)VOC and composting facilities. Part 2: (M)VOC dispersal in the environment

BACKGROUND, AIMS AND SCOPE: Composting facilities are known to release odorous volatiles due to biodegradation of municipal waste and plant residues. Although odour perception and its grading is influenced by experience, attitude and adaptation, these emissions have created a lack of acceptance for residents in the vicinity of composting facilities. Enclosure of compost pile halls, ventilation systems and biofilters are often insufficient to minimise the burden of compost-derived compounds in the air. Moreover, economic considerations forced smaller communities to establish less sophisticated facilities with open storage areas and other relevant sources for wind-borne dispersal of bioaerosols. Aim of the present study was to characterise the immission and dispersal of microbial volatiles (MVOC) and, besides, to find coincidences between MVOC and compost odour. METHODS: In the course of this study, the surroundings of two composting facilities, differing in their type of process engineering, were investigated for emission of volatiles in the environment. Both microbially and plant-derived substances were assessed, several of which have low odour thresholds. Air samples were taken in distances ranging from 50 to 800 m in a downwind direction from each facility. RESULTS AND DISCUSSION: Compost-derived and microbial volatile organic compounds (MVOC) were found at distances of up to 800 m from the composting facilities. Terpenes like alpha-pinene, camphene and camphor were the dominant compounds and coincided with typical compost odour, whereas several typical MVOC were not found at greater distances. The terpenes in combination with certain MVOC may play an important role in the perception of compost odour. Exposure concentrations were not of toxicological relevance, but sensory irritation and psychohygienic effects due to an annoyance potential of such compounds should not be dismissed. RECOMMENDATIONS AND OUTLOOK: Although terpenes are generally associated with pleasant odour characteristics, they seemed to contribute to malodours in a mixture with other VOC, in this context of volatile waste from compost facilities. Malodorous emissions from biowaste have to be considered as sources of health complaints and the investigation of mixtures of compost-derived volatiles is still inevitable. Exposure levels have to be discussed taking VOC mixtures into account. Within composting facilities, technical devices have to be improved to minimise dispersal of volatiles to prevent residents from immissions eventually causing health complaints.     

Degradation of 2,7-dichlorodibenzo-p-dioxin by Fe(3+)-H(2)O(2) mixed reagent

Fe(3+)-H(2)O(2) mixed reagent, but not Fe(2+)-H(2)O(2), was found to be capable of degrading 2,7-dichlorodibenzo-p-dioxin (DCDD). A reaction mixture of FeCl(3) (8 mM) and H(2)O(2) (1%) caused approximately 50% degradation within 6 h and >90% degradation within 24 h at 27 degrees C. Increasing the temperature remarkably stimulated degradation: at 70 degrees C, approximately 100% degradation was achieved within 15 min. When DCDD-treated model soil (5 micrograms/g) was conducted, approximately 100% of the DCDD was degraded within 30 min at 70 degrees C (both reagents were added every 10 min). These results suggest that Fe(3+)-H(2)O(2) mixed reagent may be a new tool for combating persistent environmental pollutants such as dioxins and polychlorinated biphenyls.     

Drift of 10 herbicides after tractor spray application. 2. Primary drift (droplet drift)

In the present study the primary drift of 10 herbicides was investigated in five field experiments, and the amount deposited per surface area was quantified outside the application area using simple passive dosimeters. In addition, samples for measuring a possible background value were taken upwind of the sprayed field. Deposits of spray drift were common to all spray equipment and spray was detected up to 150 m off-target. There were deposits of 0.1-9% of the applied amount close to the sprayed field (up to 2 m). But 3m from the spraying zone deposits were reduced to 0.02-4%. The amounts decreased exponentially when moving away from the field. The differences in drift could be described mainly by the different drop sizes, the wind velocity, the formulation and the filtering effect of vegetation on the sampling area. The tendency of the active ingredients to evaporate could also have an, although less important, influence on the drift. This is a factor, which ought to be exposed to a further study. The findings supported that it is the physical properties of the spray and the conditions of application (i.e. equipment and meteorology) that are the primary determinants of primary drift rather than the chemical property of the pure active ingredients.     

Surface catalyzed Fenton treatment of bis(2-chloroethyl) ether and bis(2-chloroethoxy) methane

This study examined the feasibility of using surface catalyzed Fenton treatment to remediate soil and groundwater contaminated by the chlorinated ethers, bis(2-chloroethyl) ether (BCEE) and bis(2-chloroethoxy) methane (BCEM). Parameters that affect the contaminant loss rate such as porewater pH, hydrogen peroxide concentration, and solid/water ratio were systematically evaluated. Batch reactors were set-up utilizing either contaminated or uncontaminated soil, obtained from an industrial site in Moss Point, MS, that was mixed with synthetic groundwater containing the contaminants of interest. The results show an increase in contaminant reduction with a decrease in pH, an increase in hydrogen peroxide concentration, or an increase in the solid/water ratio. For a similar set of conditions, contaminant reduction was greater for systems utilizing contaminated soil as compared to the systems containing uncontaminated soil. In addition, specific oxygen uptake rates (SOURs) were measured for biomass, collected from an activated sludge plant, exposed to different dilutions of untreated and surface catalyzed Fenton treated water to evaluate whether residual BCEE, BCEM, and their co-contaminants as well as their oxidation by-products were potentially inhibitory or can potentially serve as a substrate for the biomass. The measured SOURs show that the surface catalyzed Fenton treatment enhanced the biodegradability of the contaminated groundwater and served as a substrate for the biomass.     

CO(2)-H(2)-dependent anaerobic biotransformation of phthalic acid isomers in sediment slurries

This paper investigates the anaerobic biotransformation of three isomers of phthalic acid and benzoic acid in sediment slurries under four different atmospheres [N(2), N(2)/H(2) (19:1, v/v), CO(2), and CO(2)/H(2) (4:1, v/v)]. Significant differences were observed in lag periods and biotransformation rates among the phthalic acid isomers and under the different atmospheres. In most cases, the relative biotransformation rates of the three isomers of phthalic acid were ortho-phthalic acid>isophthalic acid>terephthalic acid. Benzoate was transformed faster than any isomer of phthalic acid. Since biotransformation of phthalic acid isomers in sediment slurries was enhanced by high initial levels of H(2) and CO(2) in the headspace, we propose a pathway for phthalic acid biodegradation in which the initial transformation to benzoate is CO(2)-H(2) dependent. Acetogenic bacteria were investigated for their possible involvement in this transformation reaction, but when MPN counts were used to compare the growth dynamics of acetogenic bacteria with the time course of the terephthalic acid transformation under N(2)/H(2) (19:1, v/v) and CO(2)/H(2) (4:1, v/v) atmospheres, the results were inconclusive.     

Abiotic reduction of antimony(V) by green rust (Fe(4)(II)Fe(2)(III)(OH)(12)SO(4).3H(2)O)

Green rust (Fe(4)(II)Fe(2)(III)(OH)(12)SO(4).3H(2)O) is an intermediate phase in the formation of iron (oxyhydr)oxides such as goethite, lepidocrocite, and magnetite. It is widely considered that green rust occurs in many soil and sediment systems. Green rust has been shown to reduce sorbed Se(VI), Cr(VI), and U(VI). In addition, it is also reported that green rust does not reduce As(V) to As(III). In this study, we have investigated for the first time the interaction between Sb(V) and green rust using XAFS and HPLC-ICP-MS. Most of the added Sb(V) was adsorbed on green rust, and Sb(III), a reduced form, was observed in both solid and liquid phases. Thus, it was shown that green rust has high affinity for Sb(V), and that Sb(V) was reduced to more toxic Sb(III) by green rust despite the high stability of the Sb(V) species even under reducing condition as reported in previous studies. Therefore, green rust can be one of the most important reducing agents for Sb(V), which can influence the Sb mobility in suboxic environments where green rust is formed.