Chlorination, side reaction during

Many industrial electrochemical systems deal with gas evolution, such as, for example, the water electrolysis, the chlorine and chlorate production or the side reactions during the electrowinning or electrodeposition of metals. 

Most of the side reactions have already been discussed in Section 26.1.3.3. (dediazoniation in organic solvents). Chlorinated aliphatic solvents, such as 1,2-dichloroethane and dichloro-methane, lead to an extensive formation of chloroaromatics, and aromatic solvents, even halogenated examples, can be arylated to some extent by arenediazonium tetrafluoroborates (vide supra). For example, during dediazoniation of benzenediazonium tetrafluoroborate in toluene, chlorobenzene, bromobenzene or anisole, 3-5 % of substituted biphenyls Ph-C6H4-X (X = Me, Cl, Br, OMe) are formed together with 0.5-0.8% of fluorobiphenyls.5 Fluorobiphenyls are formed through an ionic pathway (only 2- and 4-isomers are formed) whereas chlorobiphenyls result from a radical process (X = Cl, 2-/3-/4-isomer 26 47 27).243... 

During Swern oxidations, adventitious HC1 may be present either due to the use of impure oxalyl chloride, or due to the hydrolysis of some chlorine-containing chemical, caused by employing wet DMSO. Adventitious HC1 may cause acid-induced side reactions on sensitive substrates.174,246... 

If it is desired to carry out a chlorination, the apparatus is modified by replacing the dropping funnel and trap with a simple Y inlet tube attached directly to the reactor. One side of the Y is attached to the purge gas and the other to the chlorine source. If there is any question about the purity of the chlorine, it can be passed through a sulfuric acid wash. The chlorine flow rate during the reaction is about 300 ml./min. with no purge-gas flow. At the end of the reaction, the chlorine is purged from the system, and the product is removed as before. 

Current efficiency is here not so high as during the electrolysis of water because it is lowered by certain side reactions which occur simultaneously while the main process takes place (see equation XI-9) and (XI-10). First of all, it is chlorine which is not entirely removed from the electrolytic cell. It is partially dissolved in the electrolyte and reacts according to the nature of the medium and gives either a very slightly dissociated hypochlorous acid or a considerably dissociated hypochlorite. 

Now, let us discuss the final fate of trichloramine during disinfection. In accordance with the chloramine reactions [Reactions (17.34) to (17.36)], by the time three moles of HOCl have been added, a mole of trichloramine would have been formed. This, however, is not the case. As mentioned, while the monochloramine decomposes in a stepwise fashion to convert into the dichloramine, its destruction into the nitrogen gas intervenes. Thus, the eventual formation of the dichloramine would be less in fact, much, much less, since, as we have found, formation of the gas is favored over the formation of the dichloramine. In addition, monochloramine and dichloramine, themselves, react with each other along with HOCl to form another gas N2O [NH2CI -1-NHCI2 + HOCl N2O -I- 4H" -I- 4CL]. Also, there may be more other side reactions that could occur before the eventual formation of the dichloramine from monochloramine. Overall, as soon as the step for the conversion of the dichloramine to the trichloramine is reached, the concentration of dichloramine is already very low and the amount of trichloramine produced is also very low. Thus, if, indeed, trichloramine has a disinfecting power, this disinfectant property is useless, since the concentration is already very low in the first place. This is the reason why combined chlorine is only composed of the monochloramine and the dichloramine. Also, it follows... 

Chloroform is one of the chlorinated derivatives of methane, supplied into the atmosphere only from anthropogenic sources. It may be formed as a side product during the water chlorination by the following reactions [49] ... 

Finally, one more side reaction appears to proceed during postcrosslinking. According to elemental microanalysis, MN-200 contains 1.3% of chlorine atoms, but the band at 1260 cm, characteristic of an aromatic (PhCH2Cl) chloromethyl group [104], does not show up in the FTIR... 

Ecological Aspects of the Modified Process. Conventional treatment of the hydrolysis mixture leads to a wastewater stream whose organic load, consisting of lost product and emulsified starting material, is ca. 20 g/L COD. The organic components also contain a certain amount of combined chlorine formed as a result of side reactions with the alkane chains during sulfochlorination. 

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