Chloramine reactions

Consider the formation of the nitrate ion. The oxidation state of nitrogen in the nitrate ion is +5. Thus, this ion would not be formed from ammonia, because this would need the abstraction of eight electrons. If it is formed from the monochloramine, it would need the abstraction of six electrons, and if formed from the dichloramine, it would need the abstraction of four electrons. Thus, in the chloramine reactions with HOCl, the nitrate is formed from the dichloramine. We will, however, compare which formation forms first from the dichloramine trichloramine or the nitrate ion. The oxidation state of the nitrogen atom in trichloramine is -i-3. Thus, to form the trichloramine, two electrons need to be abstracted from the nitrogen atom. This may be compared to the abstraction of four electrons from the nitrogen atom to form the nitrate ion. Therefore, the trichloramine forms first before the nitrate ion does. 

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... 

Chloramines—Reaction products of chlorine with anunonia and organic amines. 

Haag, W. R., and Hoign, J. (1983) Ozonation of Water Containing Chlorine or Chloramines. Reaction Products and Kinetics, Water Res. 17(10), 1397-1402. 

Chloramine reactions do not release COj gas or destroy the integrity of the carbon. However, chloramine reactions are much slower than chlorine reactions with activated carbon. Finally, although carbon can effectively remove chlorine from potable water, it is more expensive than other dechlorination methods (9,10). 

The mechanism of the breakpoint reaction is, as yet, unresolved. The most comprehensive model is that of Wei and Morris who proposed a scheme consisting of reactions that formed chloramines reactions that converted chloramines into a hypothetical intermediate, NOH and reactions by which NOH decomposed to form Ns and NOa (Table 7-10). 

Kotiaho, T Lister, A.K., Hayward, M.J., Cooks, R.G. (1991) On-line Monitoring of Chloramine Reactions by Membrane Introduction Mass Spectrometry. Talanta 38 195-200. 

Free chlorine is readily dissipated in the distribution system and does not afford complete protection against bacteria due to short contact period. In order to prolong bactericidal action, free chlorine residuals are converted into more stable chloramines (reactions 3.70 3.71) by adding a little ammonia or ammonium sulphate to chlorinated water. This process is known as stabilising the chlorine. 

When a small amount of chlorine is applied to a water sample containing reducing materials (Fe, etc.), it is readily used up and so there is no residual. This stage is shown by part AB of curve II (for impure water). As the amount of chlorine applied is increased, it starts reacting with organics and also with ammonia which produces chloramines (reactions 3.70 3.71). Mono - and dichloramines arc disinfectants and are determined as combined chlorine residuals. Part BC of the curve thus shows an increase in the amounts of these chloramines. Any further increase in chlorine dosage decomposes the chloramines possibly via the following reactions ... 

Normally the chloramine immediately undergoes further reaction, giving oft nitrogen ... 

This is a stepwise process in which chloramine [10599-90-3] is first formed from ammonia and hypochlorite in a rapid reaction at low temperature ... 

This reaction is slow and requires elevated temperatures of 120—150°C under pressure. The kinetics (93,94) and mechanism (95,96) of these reactions have been studied. An undesirable competing reaction is the further oxidation of hydrazine by chloramine ... 

KetaZine Processes. The oxidation of ammonia by chlorine or chloramine in the presence of ahphatic ketones yields hydrazones (36), ketazines (37), or diaziddines (38), depending on the pH, ketone ratios, and reaction conditions (101). 

A number of perhalides aie known, and one of the most stable is ammonium tetiachloioiodide [19702 3-3] NH IQ. Ammonia reacts with chlorine in dilute solution to give chloramines, a reaction important in water purification (see Cm,ORAMINES AND BROMAMINEs). Depending upon the pH of the water, either monochloramine [10599-90-3] NH2CI, or dichloramine [3400-09-7] NHCI2, is formed. In the dilutions encountered in waterworks practice, monochloramine is neady always found, except in the case of very acidic water (see Bleaching AGENTS Water). 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

Cyanide compounds are classified as either simple or complex. It is usually necessary to decompose complex cyanides by an acid reflux. The cyanide is then distilled into sodium hydroxide to remove compounds that would interfere in analysis. Extreme care should be taken during the distillation as toxic hydrogen cyanide is generated. The cyanide in the alkaline distillate can then be measured potentiometricaHy with an ion-selective electrode. Alternatively, the cyanide can be determined colorimetricaHy. It is converted to cyanogen chloride by reaction with chloramine-T at pH <8. The CNCl then reacts with a pyridine barbituric acid reagent to form a red-blue dye. 

SuperchlorinationShock Treatment. Superchlorination or shock treatment of pool water is necessary since accumulation of organic matter, nitrogen compounds, and algae consumes free available chlorine and impedes disinfection. Reaction of chlorine with constituents of urine or perspiration (primarily NH" 4, amino acids, creatinine, uric acid, etc) produces chloramines (N—Cl compounds) which are poor disinfectants because they do not hydrolyze significantly to HOCl (19). For example, monochloramine (NH2CI) is only 1/280 as effective as HOCl against E. coli (20). 

Chloramines are formed by electrophilic attack on ammonia nitrogen via a series of bimolecular reactions, where k M ) and K (Af ) are the... 

The lack of dependence on ionic strength in the first reaction indicates that it occurs between neutral species. Mono- or dichloramine react much slower than ammonia because of their lower basicities. The reaction is faster with CI2 because it is a stronger electrophile than with HOCl The degree of chlorination increases with decreasing pH and increasing HOCINH mol ratio. Since chlorination rates exceed hydrolysis rates, initial product distribution is deterrnined by formation kinetics. The chloramines hydrolyze very slowly and only to a slight extent and are an example of CAC. 

Similar reactions occur with ammonia and HOBr (19—25), but since HOBr is a stronger electrophile than HOCl, formation rates are faster. Because of rapid bromine transfer between bromamines, equihbrium concentrations of the respective bromamines are obtained quickly. Mon ohrom amine predominates at basic pH at high N Br ratios. Below pH 8.5, NHBr2 and NBr predominate. Tribromamine formation is favored at lower pH and higher Br N ratios. The bromamines are less stable than chloramines but are better disinfectants. 

Dichloramine. The least stable chloramine, dichloramine [3400-09-7] has not been prepared in pure form. However, it has sufficient stabiUty in dilute organic or aqueous solutions for deterrnination of some physical and chemical properties. It has a pungent odor and can impart an odor or off-taste to water at concentrations above 0.8 ppm. Dichloramine can be produced by reaction of HOCl with a slight excess of NH in the pH range 4—7 or by disproportionation of NH2CI at pH 3.5—4.0 ... 

Protonated /V-chloroalkyl amines under the influence of heat or uv light rearrange to piperidines or pyrroHdines (Hofmann-Lriffler reaction) (88). The free-radical addition of alkyl and dialkyl-/V-chloramines to olefins and acetylenes yields P-chloroalkji-, P-chloroalkenyl-, and 8-chloroalkenylamines (89). Various N-hiomo- and N-chloropolyfluoroaLkylarnines have been synthesized whose addition products to olefinic double bonds can be photolyzed to fluoroazaalkenes (90). 

Reagents similai to those used in the analysis of chloiine are commonly employed in the quantitation of gaseous and aqueous chloiine dioxide as well as its reaction coproducts chlorine, chlorite, and chlorate. The volatihty of the gas from aqueous solutions as well as its reactivity to light must be considered for accurate analysis. Other interferences that must be taken into account include other oxidizers such as chloramine, hydrogen peroxide, permanganate, and metal impurities such as ferrous and ferric iron. 

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