Chlorination by hypochlorous acid

Kinetics studies of acid-catalysed chlorination by hypochlorous acid in aqueous acetic acid have been carried out, and the mechanism of the reactions depends upon the strength of the acetic acid an<( the reactivity of the aromatic. Different groups of workers have also obtained different kinetic results. Stanley and Shorter207 studied the chlorination of anisic acid by hypochlorous acid in 70 % aqueous acetic acid at 20 °C, and found the reaction rate to be apparently independent of the hydrogen ion concentration because added perchloric acid and sodium perchlorate of similar molar concentration (below 0.05 M, however) both produced similar and small rate increases. The kinetics were complicated, initial rates being proportional to aromatic concentration up to 0.01 M, but less so thereafter, and described by... 

Rather different experimental results were obtained by de la Mare et a/.208, 209, who studied chlorination by hypochlorous acid in 51, 75 and 98 % aqueous acetic acid. With the latter medium, the chlorination of anisole or m-xylene (at an unspecified temperature) was independent of the concentration of aromatic, and catalysed by perchloric acid to a much greater extent than an equimolar amount of lithium perchlorate the reaction was also catalysed by the base, sodium acetate. The reactive species was postulated as chlorine acetate produced... 

Other kinetic terms are present in chlorination by hypochlorous acid but are less important than that given above (de la Mare and Ridd, 1959a). 

Minisci, F., Vismara, E., Fontana, F., Platone, E., Farad, G. Chlorinations by hypochlorous acid free-radical versus electrophilic reactions. Chim. Ind. (Milan) 1988, 70, 52-55. 

Nitrogen trichloride can be formed during the chlorination of water containing traces of ammonia. In the chlorination by hypochlorous acid there is a slow formation of chloramine, followed by more rapid reactions that give successively dichloramine and nitrogen trichloride. The kinetic rate law (10) has been obtained, the two terms presumably indicating chlorination by HOCl and CI2 ... 

In two proposed alternative processes, the chlorine is replaced in the hypochlorination reaction by hypochlorous acid [7790-92-3] HOCl, or tert-huty hypochlorite. In the first, a concentrated (>10% by weight) aqueous solution of hypochlorous acid, substantially free of chloride, chlorate, and alkah metal ions, is contacted with propylene to produce propylene chlorohydrin (113). The likely mechanism of reaction is the same as that for chlorine, as chlorine is generated in situ through the equiUbrium of chlorine and hypochlorous acid (109). 

Hypochlorous acid reacts very rapidly and quantitatively with a slight excess of free ammonia forming monochloramine, NH2CI, which reacts at a slower rate with additional HOCl forming dichloramine, NHCI2. Trichloramine is formed when three moles of HOCl are added per mole of ammonia between pH 3—4 (100). Hypochlorous acid in the form of chlorine or hypochlorite is used in water treatments to oxidize ammonia by the process of break-point chlorination, which is based on formation of unstable dichloramine. The instabiHty of NHCI2 is caused by presence of HOCl and NCl (101,102). The reaction is most rapid at a pH of about 7.5 (103). Other nitrogen compounds such as urea, creatinine, and amino acids are also oxidized by hypochlorous acid, but at slower rates. Unstable iV-chloro compounds are intermediates in deammination of amino acids (104,105). 

The conditions for chlorate formation are high pH, low reactant concentrations, and the presence of excess chlorine or hypochlorous acid. Thus, the addition of free chlorine or hypochlorite to chlorine dioxide treated water, which contains chlorite as a by-product of the chlorine dioxide treatment, predominandy forms chlorate in the pH 5—8 range typically used in water treatment (140). 

Chlorination of thiiranes in hydroxylic solvents gives /3-chloroethylsulfonyl chlorides due to further oxidation of the intermediate sulfenyl chloride by chlorine or hypochlorous acid (Scheme 40). Polymer is usually obtained also unless the reaction is done in concentrated hydrochloric acid, which causes rapid ring cleavage to 2-chloroethylthiols which are subsequently oxidized to the sulfonyl chlorides. An 85% yield of (37) is obtained in concentrated hydrochloric acid-HCl(g) whereas only a 15% yield is obtained in CCI4-H2O. 

The complex kinetic expression for chlorination of anisole by hypochlorous acid (p. 577) becomes simpler for both less reactive and more reactive substrates. For benzene, the expression is... 

Derbyshire and Waters202 carried out the first kinetic study, and showed that the chlorination of sodium toluene-m-sulphonate by hypochlorous acid at 21.5 °C was catalysed more strongly by sulphuric acid than by perchloric acid and that the rate was increased by addition of chloride ion. A more extensive examination by de la Mare et al.203 of the rate of chlorination of the more reactive compounds, anisole, phenol, and />-dimethoxybenzene by hypochlorous acid catalysed by perchloric acid, and with added silver perchlorate to suppress the formation of Cl2 and C120 (which would occur in the presence of Cl" and CIO-, respectively),... 

The pH of the water is checked again and made slightly basic to reduce acid corrosion of the pipes. At this point, a disinfectant, usually chlorine, is added. In the United States, the chlorine level is required to be greater than 1 g of Cl2 per 1000 kg (1 ppm by mass) of water at the point of consumption. In water, chlorine forms hypochlorous acid, which is highly toxic to bacteria ... 

Kroy A variation on the Hercosett process for making wool fire-resistant. The chlorination step is effected by hypochlorous acid. Invented in Toronto in 1975 by F. Mains of Kroy Unshrinkable Wools. 

During the long Antarctic night, appreciable amounts of molecular chlorine, Cl, and hypochlorous acid, HOCl, accumulate within the polar vortex. When the sun returns during the spring (in September in Antarctica), ultraviolet radiation decomposes the accumulated molecular chlorine and hypochlorous acid to produce atomic chlorine. Cl. Atomic chlorine is a free radical. Free radicals are atoms or molecules that contain an unpaired or free electron. The Lewis structures of free radicals contain an odd number of electrons. The unpaired electron in free radicals makes them very reactive. The free radical Cl produced from the decomposition of CI2 and HOCl catalyzes the destruction of ozone as represented by the reaction ... 

Constitution.—Hypochlorous acid, HOC1, is a very weak acid despite the presence of the non-metal chlorine, which gives to hydrochloric acid, HC1, such powerful acidic properties. D. Vorlander,15 therefore, assumed that the constitution is not H.C1 0, since such an acid would have a strength comparable with that of hydrochloric acid he considers that the chlorine of hypochlorous acid is polyvalent and unsaturated, and accordingly writes the formula HO.Cl. This, says he, is in accord with (i) its feeble acidic properties (ii) its ready oxidizibility to chloric acid and (iii) the ease with which it is decomposed—particularly into Cl and OH. The relation between water, hypochlorous acid, and chlorine monoxide is graphically shown by the formula ... 

A. J. Balard found that gold or platinum are not affected by hypochlorous acid, either alone or mixed with sulphuric or nitric acid. The last-named mixture, however, would probably act on both metals owing to the formation of free chlorine. No gold hypochlorite has yet been prepared. 

Glycol is made by reaction of ethylene and chlorine or hypochlorous acid to form ethylene dichloride or ethylene chlorohydrin. respectively, followed by treatment of either of these with sodium carbonate solution heated under pressure. Glycol is also formed when ethylene is treated with potassium permanganate. 

Carr AC, van den Berg JJM, Winterboum CC (1996) Chlorination of Cholesterol in Cell Membranes by Hypochlorous Acid. Arch Biochem Biophys 332 63... 

Masuda M, Suzuki T, Friesen MD, Ravanat J-L, Cadet J, Pignatelli B, Nishino H, Ohshima H (2001) Chlorination of Guanosine and Other Nucleosides by Hypochlorous Acid and Myeloperoxidase of Activated Human Neutrophils. J Biol Chem 276 40486... 

Chlorination by aqueous chlorine or its derivatives is a widespread oxidation technique used in the disinfection of natural and waste waters. Oxidation by hypochlorous acid is also used in vivo as part of an unspecific defence system in mammals. 

M. Masuda et al., Chlorination of guanosine and other nucleosides by hypochlorous acid and myeloperoxidase of activated human neutrophils. J. Biol. Chem. 276, 40486-40496 (2001)... 

Beach, M.W. and Margerum, D.W. (1990) Kinetics of oxidation of tetracyanonickelate(II) by chlorine monoxide, chlorine, and hypochlorous acid and kinetics of chlorine monoxide formation. Inorg. Chem. 29, 1225-1232. 

The oxidation pathways of chlorine dioxide under actual conditions are complex because a number of species including chlorine, hypochlorous, chlorous, and chloric acids are formed as intermediates. A rapid conversion of chlorine dioxide to chloride and chlorite (chlorous acid, pK 2.0) may first take place, followed then by a slow phase during which mainly the chlorite reacts with the pulp components. However, continuous generation of chlorine dioxide during bleaching takes place, for example, by the reaction between chlorite and chlorine (or hypochlorous acid) ... 

Nitrogen trichloride is also produced by electrolysis of NH4CI solutions. The reaction is carried out in a buffer system because of the formed HCl. NCI3 can be extracted with organic solvents like carbon tetrachloride. Ammonium ions can be chlorinated with hypochloric acid at pH 3 -4 ... 

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