Dechlorination reaction agents

Aryl halides can be dehalogenated by Friedel-Crafts catalysts. Iodine is the most easily cleaved. Dechlorination is seldom performed and defluorination apparently never. The reaction is most successful when a reducing agent, say, Br or 1 is present to combine with the I" or Br coming off." Except for deiodination, the reaction is seldom used for preparative purposes. Migration of halogen is also found," both intramolecular and intermolecular." The mechanism is probably the reverse of that of 11-11." ... 

The novel antitumor agent penclomedine (11.38) provides another example of multiple dehalogenation [74], In the perfused rat liver, rapid biotransformation occurred by two major pathways, namely oxidative O-demethyla-tion at C(4), and formation of penclomic acid by dechlorination of the CC13 moiety. The proposed sequence of reactions ... 

Effluents from sewage treatment plants are not allowed to contain residual chlorine in excess of tolerable values as determined by water quality standards. For example, in discharges to trout streams, the residual chlorine should not exceed 0.02 mg/L. Thus, chlorinated effluents should be dechlorinated. Sulfur dioxide, sodium sulfite, sodium metabisullite, and activated carbon have been used for dechlorination. Because sulfur dioxide, sodium sulfite, and sodium metabisulfite contain sulfur, we will call them sulfur dechlorinating agents. Dechlorination is an oxidation-reduction reaction. The chemical reactions involved in dechlorination are discussed next. 

Chemical Reactions Using Suleur Dechlorinating Agents... 

Irrespective of the type of residual chlorine present, all the species can be represented by a single species by means of the equivalence of chemical reactions. It is convenient to use HOCl to represent all these species. Thns, the chemical reactions using snlfnr dioxide as the dechlorinating agent with HOCl representing the residual chlorine species are as follows ... 

Sodium sulfite is Na2S03. Thus, the chemical reactions using sodium sulfite as the dechlorination agent are as follows ... 

Although precise control may be achieved in dosing the sulfm dechlorinating agents, some residual will exist. This residual should be minimized not only because of waste of chemicals but also because of its effect on the dissolved oxygen of receiving streams. The reactions of these residuals on oxygen are as follows for sulfm dioxide ... 

The photolytic degradations of drugs are complex, and include reactions such as oxidations, reductions, cis-trans isomerizations, structural rearrangements, hydrolyses, dechlorinations, etc. Oxidation is one of the major pathways of photochemical reactions. Table 1 lists the pathways of photochemical decomposition of some therapeutic and nontherapeutic agents. 

Following the chlorine chemical contact for disinfection, described in the previous section, residual chlorine must be removed using a dechlorination agent such as sulfur dioxide (Fig. 8). This quenching of the chlorine (or chloramine) by a strong reductant provides a potential for the chemical reduction of transformation products in the wastewater. Minimal research has addressed these reductive reactions for transformation products of synthetic organic chemicals. 

Whichever form of is used, the active agent will be the same. In solution, proton shifts between the different forms are rapid [217], and which form takes part in the reaction depends entirely upon the pH of the brine. Since secondary dechlorination of brine usually follows or accompanies the addition of alkali, the sulfite ion is the predominant form. Miron [218] reports that it is also the most active. The following equilibria apply ... 

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