Chlorine addition/removal

Because enones are much more reactive towards dissolving metal reductions than nonactivated double bonds it is possible to selectively reduce the former in the presence of the latter type of double bond (Table 5, entries 1, 5 and 6). Furthermore, inverse addition of the lithium in ammonia solution to the substrate dissolved in diethyl ether allows selective reduction in the presence of other highly sensitive functional groups such as vinyl chlorides (entry 5). Under normal reaction conditions the chlorine is removed yielding the corresponding olefin49. 

Addition polymerization leads preponderantly to the head-to-tail structure. Marvel (20) and coworkers carried out dechlorination of the polymer in boiling dioxane with zinc dust. In this procedure, chlorine is removed to yield cyclopropane rings and zinc chloride. The dechlorinated material contained 13-16% retained chlorine. Although this favors the head-to-tail arrangement, it does not preclude a certain amount of head-to-head or tail-to-tail product. However, the residual chlorine content corresponds to that expected from the random attack of zinc on a head-to-tail polymer structure. 

Chlorine has been added to the feedwater upstream of reverse osmosis pretreatment. However, since chlorine will depolymerize the polyurea membrane barrier layer in the spiral wound element, with subsequent loss of desalination properties, the chlorine is removed in the pretreatment system dechlorination basin. This removal is chemically accomplished by the addition of sodium bisulfite. The chlorine level in the influent and effluent to the dechlorination basin is continuously monitored. The feedwater is then transferred from the dechlorination basin to the cartridge filter feed pumping station by gravity flow and it is then pumped to the cartridge filters. 

More recently, Negri et al. [75,77] have shown that the outer lipid layer of epicuticle is predominately 18-methyleicosanoic acid [75], a branched fatty acid consisting of 21 carbon atoms, and this fatty acid represents about 25% of the epicuticle. These authors have proposed a model of the epicuticle wherein the fatty-acid layer is connected to the underlying fibrous protein layer through thioester linkages involving the cysteine residues of the protein [76]. Negri and Cornell [77] have also shown that alcoholic alkali and chlorine treatments remove the fatty-acid layer from the cuticle. In addition, similar unstained layers exist between cortical cells, but these are not removed by alcoholic alkali treatments [77]. 

Removing a free oxygen atoms also reduce ozone since one less ozone molecule will be formed via reaction 17.4.2. Thus, the chlorine atom reactions effectively remove two ozone molecules by destroying one and preventing the formation of another. Additionally, the original chlorine atom is regenerated to catalytically destroy more ozone. This reaction cycle can proceed thousands of times, destroying up to 100,000 molecules of O3 before the chlorine is removed from the system (e.g., by the formation of HCl). 

As remarkable as the performances of these membranes are, aU aromatic PA membranes have one severe drawback their susceptibility to degradation by chlorine. The removal of chlorine prior to membrane separation by activated carbon, sodium sulphite (Na2S03), or sodium bisulphite (NaHSOa) addition is, therefore, mandatory. Dechlorination by NaHSOs in stoichiometric excess can, however, be ineffective in seawater feed because dissolved oxygen in seawater reacts with the chemical. Further, the absence of chlorine can lead to biofouling that is often irreversible. 

Free chlorine is removed by addition of an equivalent quantity of sodium thiosulphate solution (1 ml 0.01 m solution approx. OA m CI2). 

The standard solutions are stable at the 0.01 mol/L level for several months. The working standards should be prepared by serial dilution irmnediately before use. The stability of dilute antimony(///) standard solutions may be highly variable. In some instances we have found oxidation to antimony(V) to be almost complete after only a few hows, while some solutions showed little oxidation over several months. We suspect that trace amounts of oxidants present in the water used for dilution (e.g., reactive chlorine not removed by the purification process) may be responsible for this problem. We suggest that standard dilutions be prepared immediately before use and that the stability of the standards in the particular water used in the laboratory be tested. If problems persist, the dilutions may be prepared using a natural water sample containing little or no antimony(///). The addition of ca. 1 g ascorbic acid per 1000 mL of solution also improves the stability of antimony(///) standards. 

Dichloratnine, pH 4.5, and trichloramjne, pH 4.4, are formed by successive additions of CI2 or HOCl to the monochloramine. Chloramines impart a green color to water. As the hypochlorite ion is consumed by oxidizing the cmitantinants, the chloramines supply more HOCl and so maintain a safe level of primary disinfectant. Excess chlorine is removed by reactitm with sodium bisulfate ... 

Prior to the resaturation, the byproduct chlorate and dissolved chlorine must be eliminated from the anolyte. Chlorate concentration is controlled by acidification of a partial stream of anolyte with an excess of hydrochloric acid [144]. Chlorine is removed under vacuum followed by addition of sodium bisulfite and hydroxide. 

A mixture of 0.10 mol of the acetylenic alcohol, 0.12 mol of triethylamine and 200 ml of dichloromethane (note 1) was cooled to -50°C. Methanesulfinyl chloride (0.12 mol) (for its preparation from CH3SSCH3, (08300)30 and chlorine, see Ref. 73) was added in 10 min at -40 to -50°0. A white precipitate was formed immediately. After the addition the cooling bath was removed and the temperature was allowed to rise to -20°0, then the mixture was vigorously shaken or stirred with 100 ml of water. The lower layer was separated off and the aqueous layer was extracted twice with 10-ml portions of CH2CI2. The combined solutions were dried over magnesium sulfate and concentrated in a water-pump vacuum (note 2). The yields of the products, which are pure enough (usually 96%) for further conversions, are normally almost quantitative. 

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