2,4,5-Trichlorophenol, concentration

Diaz-Diaz et al., 2011 describes an electrochemical sensors based on a catalytic 2,4,6-trichlorophenol molecularly imprinted microgel that rnirnics the dehalogenative function of the natural enzyme chlorofjeroxidase for p>-halophenols. Two strategies were explored a carbon paste modified with the polymer and the drop)-coating of screen-fainted electrodes with powder suspensions of the polymer and carbon nanotubes. With this last design, 2,4,6-trichlorophenol concentrations above 25 mM could be detected. 

Hexachlorophene, a substance used in the manufacture of germicidal soaps, is prepared by reaction of 2,4,5-trichlorophenol with formaldehyde in the presence of concentrated sulfuric acid. Propose a mechanism for the reaction. 

The rate constants for phenol release (2,4,6-trichlorophenol TCP) were determined spectrophotometrically at 298 nm in both the presence and the absence of the fluorophore (DPA) and were shown to be independent of DPA at the concentrations employed. The time-dependent release of TCP monitored at 298 nm, which is shown in... 

Degradation of contaminants may occur with bacteria that have been isolated from pristine environments without established exposure to the contaminants, and exhibit no dependence on substrate concentration. For example, organisms from a previously unexposed forest soil were able to degrade 2,4,6-trichlorophenol at concentrations up to 5000 ppm, and terminal restriction fragment length polymorphism analysis revealed that at concentrations up to 500 ppm, the bacterial community was unaltered (Sanchez et al. 2004). 

Many toxic pollutants were detected in the process wastewaters from metal molding and casting processes. The toxic pollutants detected most frequently in concentrations at or above 0.1 mg/L were phenolic compounds and heavy metals. The pollutants include 2,4,6-trichlorophenol, 2,4-dimethyl-phenol, phenol, 2-ethylhexyl, cadmium, chromium, copper, lead, nickel, and zinc. Each type of operation in the foundry industry can produce different types of pollutants in the wastewater stream. Also, because each subcategory operation often involves different processes, pollutant concentrations per casting metals may vary. 

The environmental burden of waterways with polychlorinated dibenzo-p-dioxins (PCDD) has been at the forefront of public and regulatory concern, because of the toxicity associated with particularly the 2,3,7,8-(laterally) substituted congeners, which have a tendency to bioaccumulate throughout the trophic food chain. Contamination of aquatic sediments by dioxins includes both non-point (e.g., atmospheric deposition) and point sources (e.g., industrial effluents, combined sewage overflows), and is generally characterized by a dominance of hepta- and octa-CDD, with minor contributions of hexa- to tetra-CDD [429]. Elevated concentrations of the 2,3,7,8-TCDD isomer tend to be associated with direct discharge from sources such as 2,4,5-trichlorophenol production [54,430]. 

Source Although not produced commercially, TCDD is formed as a by-product in the synthesis of 2,4,5-trichlorophenol. TCDD was found in 85% of soil samples obtained from a trichlorophenol manufacturing site. Concentrations ranged from approximately 20 ng/kg to 600 g/kg (Van Ness et al, 1980). TCDD may be present in the herbicide 2,4-D which contains a mixture of dichloro-, trichloro-, and tetrachlorodioxins. TCDD is commonly found as a contaminant associated with pulp and paper mills (Boddington, 1990). In addition, during the manufacture of 2,4,5-T and silvex from trichlorophenol, TCDD was found at concentrations averaging 20 parts per billion (Newton and Snyder, 1978). 

Biological. Under aerobic conditions, biodegradation products may include 1,2-di-chlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, and carbon dioxide (Kobayashi and Rittman, 1982). A mixed culture of soil bacteria or a Pseudomonas sp. transformed 1,2,4-tri-chlorobenzene to 2,4,5- and 2,4,6-trichlorophenol (Ballschiter and Scholz, 1980). When 1,2,4-trichlorobenzene was statically incubated in the dark at 25 °C with yeast extract and settled domestic wastewater inoculum, significant biodegradation occurred, with gradual acclimation followed by a deadaptive process in subsequent subcultures. At a concentration of 5 mg/L, 54, 70, 59, and 24% losses were observed after 7, 14, 21, and 28-d incubation periods, respectively. At a concentration of 10 mg/L, only 43, 54, 14, and 0% were observed after 7, 14, 21, and 28-d incubation periods, respectively (Tabak et al., 1981). In activated sludge, <0.1% mineralized to carbon dioxide after 5 d (Freitag et al., 1985). 

Chemical/Physical. Chemical oxidation of mono-, di-, and trichlorophenols using Fenton s reagent were investigated by Barbeni et al. (1987). To a 70-mL aqueous solution containing 4-chlorophenol thermostated at 25.0 °C was added ferrous sulfate and hydrogen peroxide solution (i.e., hydroxyl radicals). Concentrations of 4-chlorophenol were periodically determined with... 

After most of the solvent has been distilled off, the reaction mixture is acidified the trichlorophenol can be free from TCDD by one or two distillations, with the result that the TCDD is concentrated in the residues. An episode involving accidental poisoning in horse arenas in Missouri, USA, in 1971 clearly shows the hazards of such residues 2). 

You have the job to determine the concentrations of 2,4,6-trichlorophenol (2,4,6-TCP) and 4-ethyl-2,6-dimethylpyridine (EDMP) in wastewater samples from an industrial site. You decide to extract the compounds first into an organic solvent, and then analyze them by liquid chromatography. From the Kitw values reported for the two compounds for various solvent-water systems, you conclude that there seems to be no single solvent that is optimally suited to extract the two compounds simultaneously. Would this be wise anyway If there were such a solvent, at what pH would you carry out the extraction What would be the problem Anyway, you decide to extract first 2,4,6-TCP with butylacetate (subscript b) and then EDMP with trichlo-romethane (chloroform, subscript c). Give the pH-conditions at which you perform the extractions and calculate how much solvent you need at minimum in each case if you want to extract at least 98% of the compounds present in a 100 mL water sample. 

XAD-2 macroreticular resin columns. This situation implied that the XAD-2 column was not effective in retaining completely all the solutes present in the water samples. [NOTE The XAD-2 resin column contained about 25% more packing, and the rate of percolation was about the same as that normally used for processing 200 L of tap water (21).] In addition, a variety of volatiles that appeared immediately following the solvent peak were also present. Subsequent analysis of these concentrates by GC-MS indicated the presence of 6-chloro-2,4-diamino-1,3,5-triazine (tentative), 2,5-diphenylisoxazole (tentative), tributoxyethyl phosphate (confirmed), bis(2-ethylhexyl) phthalate (confirmed), and dimethylbenzoic acid (confirmed) from site 1. The concentrate from site 2, however, showed the presence of 2,4,5-trichlorophenol (confirmed), BHC (confirmed), 2,5-diphenylisoxazole (tentative), bis(2-ethyl-hexyl) phthalate (confirmed), trimethylbenzene (confirmed), ethylbenz-aldehyde (confirmed), ethylacetophenone (confirmed), hexanoic acid (confirmed), and 4-cyano-3,7,ll-tridecatriene (tentative). 

The k can be obtained using the initial rate method by overdosing H202. For example, at the overdosed H202 concentration of 5 x 10 M and constant pH of 3.5, the k can be obtained by plotting the l/r0vs. 1/Fe2+ during the dechlorination of 2,3,4-trichlorophenol. 

As discussed earlier, the effects of the meta, para, and ortho positions of chlorine on the dechlorination kinetics of monochlorophenols, dichlorophenols, and trichlorophenols during Fenton oxidation were evaluated by comparing the rate constants of the kinetic model (Tang and Huang, 1995). This study proposed a pseudo first-order steady state with respect to organic concentration. The proposed reaction pathways considered that the hydroxyl radicals would attack unoccupied sites of the aromatic ring. 

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