4-chlorophenol concentrations

Figure 2B also shows that the first-order rate constants of 4-chlorophenol degradation are inversely proportional to the initial 4-chlorophenol concentration, whereas the initial rate constants are proportional to the initial 4-chlo-rophenol concentration. When the reciprocals of the initial rate constants are... 

Figure 2. Part A Degradation of 4-chlorophenol versus time at 3.0 ( ), 1.0 (0), 0.3 (Q), 0.10 (9), and 0.03 (A) mM 4-chlorophenol. Experimental conditions TiO2 = 1 g/L, pH = 4.0, I = 5 X 10r2 M NaN03, oxygen atmosphere, and temperature = 25 °C. Part B The first-order rate constants (Q) and the initial rate constants (%) versus the initial 4-chlorophenol concentration. Part C The reciprocals of the initial rate constant versus reciprocals of the initial 4-chlorophenol concentration.

The extent of degradation in the biopiles was proportional to the starting chlorophenol concentration. Overall, however, chlorophenol loss was between 80 and 90%. Where highly contaminated soil was treated (original chlorophenol concentration 850mgkg 1) the rate of loss was between 2 and 5mg (kgdrywt) 1 d 1. This is a fast rate of chlorophenol loss and the remediation process was complete within 3 months. 

FIGURE 15.25 Theoretically predicted lines for different /j-chlorophenol concentrations on carbon-predicted from solid line of concentration 400 X 10 kgm . ... 

Many very hazardous solvents, such as benzene and carbon tetrachloride, were widely used until the 1970s. The situation was very similar for the use of pesticides. Among the toxic pesticides that were still in wide use 20 years ago were chlorophenols, DDT, lindane, and arsenic salts, all of which are classified as human carcinogens as well as being acutely toxic. Fortunately, use of these kinds of very toxic chemicals is now limited in the industrialized world. However, because the number of chemicals used in various industries continues to increase, the risks of long-term health hazards due to long-term exposure to low concentrations of chemicals continues to be a problem in the workplace. 

Synthesis of TGDD in sunlight could not be expected to add appreciably to this environmental burden. The formation rate from chlorophenols is strongly concentration-dependent, and its mechanism requires... 

PCP presents a different picture from that of the lower chlorophenols and their derivatives. The corresponding dioxin shows much more stability to light than does TCDD, enough to permit its prolonged existence at low concentrations in a photoreactor. As a phenol it can directly yield dioxins, a process favored by its normal mode of application as the sodium salt. Although octachlorodibenzo-p-dioxin has much lower mammalian toxicity than TCDD (6), its formation, properties, and effects demand additional investigation. Technical preparations of PCP are frequently mixtures of tetra- and pentachlorophenols consequently, hepta-and possibly hexachlorodibenzo-p-dioxins might be expected as photolysis products in addition to the octachloro derivative. 

The objectives of the soil persistence experiments were (1) to learn the effect of soil type and concentration on the TCDD degradation rate, (2) to isolate and characterize degradation products from DCDD and TCDD, and (3) to determine whether chlorodioxins could be formed from chlorophenol condensation in the soil environment. This last study was essential since quality control at the manufacturing level could reduce or eliminate the formed dioxin impurity. But the biosynthesis of chlorodioxins by chlorophenol condensation in the soil environment could not be controlled and would have connotations for all chlorophenol-de-rived pesticides if formation did occur. The same question needed to be answered for photochemical condensation reactions leading to chloro-... 

The tolerance of the strains to high concentrations of pentachlorophenol—S. chlorophenolica appears to be less sensitive than M. chlorophenolicus (Miethling and Karlson 1996). This may be attribnted to the ability of the cells to adapt their metabolism to avoid synthesis of toxic concentrations of chlorinated hydroquinones, and is consistent with the low levels of these metabolites measnred in the cytoplasm of cells metabolizing pentachlorophenol (McCarthy et al. 1997). Inocnla have also been immobilized on polyurethane that, in addition, ameliorates the toxicity of chlorophenols (Valo et al. 1990). 

Sedarati, M.R., Keshavarz, T., Leontievsky, A.A., and Evans, C.S., Transformation of high concentrations of chlorophenols by the white-rot basidiomycete Trametes versicolor immobilized on nylon mesh. Electronic J. Biotechnol. [online], 6(2), August 15, 2003. 

A number of carboxylic acids other than acetic were investigated as solvents or promoters. All of these acids which were stable to reaction conditions were found to be effective in promoting glycol ester production (e.g., propionic, pivalic, benzoic, etc.). However, other Br nsted acids of non-carboxylic nature were not found to be effective promoters. Thus penta-chlorophenol, although it has a pKa value (4.82) very close to that of acetic acid (4.76), is not a comparable promoter (Table I, reaction 13). Likewise, phosphoric acid (pK 2.15) is not an effective solvent or co-solvent with acetic acid (Table I, reaction 8). Experiments with lower concentrations of these acids in sulfolane solvent also showed that carboxylic acids are unique in promoting glycol formation. The promoter function of carboxylic acids thus appears not to be dependent (only) upon their acidity, but on some other chemical or structural property. 

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