Subject dechlorination

In order to ensure the destruction of pathogens, the process of chlorination must achieve certain control of at least one factor and, preferably two, to compensate for fluctuations that occur. For this reason, some authorities on the subject stress the fact that the type and concentration of the chlorine residual must be controlled to ensure adequate disinfection. Only this way, they claim, can chlorination adequately take into account variations in temperature, pH, chlorine demand and types of organisms in the water. While possible to increase minimum contact times, it is difficult to do so. Five to ten minutes is normally all the time available with the type of pressure systems normally used for small water supplies. Many experts feel that satisfactory chlorine residual alone can provide adequate control for disinfection. In their opinion, superchlorination-dechlorination does the best job. Briefly, what is this technique and how does it operate ... 

The production of tetracycline by catalytic dechlorination is described in U.S. Patent 2,699,054 as follows Pure chlortetracycline (4.8 grams) was suspended in 100 ml of methanol and sufficient anhydrous dioxane was added to completely dissolve the product. To the solution was added 0.5 gram of 5% palladium-on-charcoal catalyst. The mixture was placed in a conventional hydrogenation apparatus and subjected to a pressure of 50 psi of hydrogen while being agitated. 

Chlorinated dibenzo ip-dioxins are contaminants of phenol-based pesticides and may enter the environment where they are subject to the action of sunlight. Rate measurements showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is more rapidly photolyzed in methanol than octachlorodi-benzo-p-dioxin. Initially TCDD yields 2,3,7-trichlorodiben-zo-p-dioxin, and subsequent reductive dechlorination is accompanied by ring fission. Pure dibenzo-p-dioxin gave polymeric material and some 2,2 -dihydroxybiphenyl on irradiation. Riboflavin-sensitized photolysis of the potential precursors of dioxins, 2,4-dichlorophenol and 2,4,5-trichloro-phenol, in water gave no detectable dioxins. The products identified were chlorinated phenoxyphenols and dihydroxy-biphenyls. In contrast, aqueous alkaline solutions of purified pentachlorophenol gave traces of octachlorodibenzo-p-dioxin on irradiation. 

We have chosen the PVC diad and triad compounds 2,4-dichloropentane (DCP) and 2,4,6-trichloroheptane(TCH) as subjects for our attempt to obtain quantitative kinetic data characterizing their (n-Bu)3SnH reduction in the hope that they will serve as useful models tor the reduction of PVC to E-V copolymers. Unlike the polymers (PVC and E-V), DCP and TCH are low molecular weight liquids whose high resolution 13C NMR spectra can be recorded from their concentrated solutions in a matter of minutes. Thus, it is possible to monitor their (n-Bu)3SnH reduction directly in the NMR tube and follow the kinetics of their dechlorination. 

Specific effluents have also been subjected to WRF-mediated remediation studies. Decolourization, dechlorination and detoxification of highly toxic bleach plant effluents derived from the pulp and paper industry have been reported [26-28], while degradation and decolourization of synthetic dyes due to the non-specificity of the LMEs have been widely documented [29, 30], Likewise, treatment of the acidic, phenolic-rich olive oil mill wastewater has shown COD reduction, decolourization and dephenolization [31-34],... 

In activated sludge, 80.6% degraded after a 47-h time period (Pal et al., 1980). Chemical/Physical. Zhang and Rusling (1993) evaluated the bicontinuous microemulsion of surfactant/oil/water as a medium for the dechlorination of polychlorinated biphenyls by electrochemical catalytic reduction. The microemulsion (20 mL) contained didodecyldi-methylammonium bromide, dodecane, and water at 21, 57, and 22 wt %, respectively. The catalyst used was zinc phthalocyanine (2.5 nM). When PCB-1221 (72 mg), the emulsion and catalyst were subjected to a current of mA/cm on 11.2 cm lead electrode for 10 h, a dechlorination yield of 99% was achieved. Reaction products included a monochlorobiphenyl (0.9 mg), biphenyl, and reduced alkylbenzene derivatives. 

An useful alternative to the already known retropinacol reactions is presented by Liu and co-workers [7], This works demonstrates that pinacols bearing (dimethylamino)phenyl substiments can be subjected to fast oxidative fragmentation via photoinduced electron transfer with chloroform as the electron acceptor in yields up to 80%. The extremely fast dechlorination of the chloroform radical anion inhibits back-electron transfer and thus leads to effective fragmentation of the pinacol radical cation (Scheme 8). 

A well-stirred suspension of 1-phenylcyclohexene (3.75 g, 23.7 mmol) and freshly prepared activated Zn (3.9 g, 59.3 mmol) in anhyd Et20 (150 mL) was brought to reflux. Trichloroacetyl bromide (16.1 g, 71.1 mmol) in anhyd Et20 (70 mL) was added dropwise to the stirred suspension over a period of 4-6 h while additional Zn (14.7 g, 225 mmol) was added portionwise over the same period. Refluxing was continued for an additional 2-4 h. The mixture was filtered through Celite and the filtrate washed with several aliquots of H20. After drying (MgS04), the solvent was removed in vacuo and the crude dichlorocyclobutanone 1 was subjected to reductive dechlorination as follows to a solution of crude ketone 1 in HOAc was added... 

A flask with a septum-capped side tube was attached by rubber vacuum tubing via a U-trap to a vacuum line. The flask was charged with 3,4-dichlorodecafluoro-i m/i-tricyclo[4.2.0.02-5]octane (1.74 g, 4.87 mmol), activated Zn dust (1.05 g, 16.1 mmol), and DMSO (30 mL). The mixture was subjected to 2 freeze-pump-thaw cycles, then the flask was attached to a rocking motor and immersed in an ultrasonic bath. The U-trap was cooled in liquid N2. and the pressure in the system was maintained at ca. 20 Torr while the flask was rocked and subjected to sonication. Dechlorination began immediately and was finished in 20-30 min collection of the product in the U-trap was complete after 2.5 h yield 0.79 g (57%). 

Sulfite, S032-, is a bivalent polyanion. It occurs in boiler feed water that is treated with sulfite for controlling dissolved oxygen. It also occurs in waters subjected to S02 treatment for dechlorination purpose. Sulfite forms sulfurus acid, H2S03, which gradually oxidizes to sulfuric acid. Excess sulfite in boiler waters can cause corrosion. Sulfite is toxic to aquatic life. 

Dechlorination of 4-chloro-6-methylthieno[2,3-d]pyrimidine 164 with zinc in ethanol and acetic acid at 80°C gave compound 165. The latter was subjected to the Reissert reaction using two equivalents each of tributyltin cyanide and acyl chloride in dichloromethane at room temperature. With benzoyl chloride the mono-Reissert adduct 166 was obtained, whereas with acetyl chloride the di-Reissert product 167 (86JHC545). 

Many groundwaters are contaminated with the cleaning solvents trichloroethylene (TCE) and perchloroethylene (PCE). They are two of the most common organochlorine compounds found in Superfund sites. Radiation-induced decomposition of TCE in aqueous solutions has been the subject of several recent studies [15-20]. In most of the referenced studies, the complete destruction of TCE was observed. Dechlorination by a combination of oxidative and reductive radiolysis was stoichiometric. Gehringer et al. [15] and Proksch et al. [18] have characterized the kinetics and mechanism of OH radical attack on TCE and PCE in y-ray-irradiated aqueous solution. Trichloroethylene was readily decomposed in exponential fashion, with a reported G value of 0.54 pmol J-1. A 10 ppm (76 pM) solution was decontaminated with an absorbed dose of less than 600 Gy. For each OH captured, one C02 molecule, one formic acid molecule and three Cl- ions were generated. These products were created by a series of reactions initiated by OH addition to the unsaturated TCE carbon, which is shown in Eq. (45) ... 

PAHs also react with OH. Removal of PAHs from the atmosphere by photolytic production of OH may be an important natural remediation mechanism. Because these compounds have limited water solubility, most studies have investigated gas phase reactions. Naphthalene was shown to be subject to a complex series of hydroxylations and peroxyl-induced ringopening reactions leading to the production of organic acids [37]. Although PAHs have low water solubility, they are often important water pollutants, attached to particles or colloids suspended in solution, or in aqueous sediments. PCBs have been shown to be susceptible to OH attack, resulting in dechlorination [38]. 

All pesticides that can come into contact with the environment are subject to a risk assessment. The basis for this risk assessment is provided by data from environmental fate and environmental toxicity studies, which are carried out in the laboratory or under field conditions. The fate (adsorption, degradation, and mobility) of the active substance must be studied in soil, air, water, and sediments. The laboratory studies are frequently performed with C-labeled substances to make the mass balance easier. It is important to know how a substance degrades in the environment, because sometimes the degradation products are more persistent than the parent substance. DDT, for instance, is converted to metabolites by stepwise dechlorination (Eq. 11.9). The metabolites (e.g., DDD or DDA) can be found in soil for many years after the DDT itself is degraded. 

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