By Hypohalous Acids

HOCl may also indirectly damage DNA through interaction with nitrite to yield nitryl chloride at inflammatory sites. The major products from nitryl chloride attack on guanine or DNA are 8-nitroguanine and 8-nitroxanthine [50]. This reaction is predicted to be feasible in vivo,based on the known con- 

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Nitryl chloride, formed from peroxynitrite and HOCl is also capable of nitrating, chlorinating and hydroxylating tyrosine [ 116]. However, the reduction of nitrotyrosine by hypohalous acid has also been demonstrated. Several recent studies indicate that peroxynitrite can lead to generation of both nitrated and hydroxylated phenylalanine residues. The formation of 3-nitrotyrosine and 4-nitrophenylalanine was favoured over the hydroxylation reaction when phenylalanine was treated with peroxy nitrite in vitro [117]. 

The kinetic data on addition of halogen, interhalogens, and hypohalous acids are collected in Table 5. The Table is subdivided according to the reagents initiating the addition free halogens appear first, followed by hypohalous acids. The kinetic form is shown by reference to equations quoted... 

FIGURE 4.2 Sequential targeting of plasmalogen reactive sites by hypohalous acids. Hypohalous acids (HOX) first target the vinyl ether bond of plasmalogens and then the alkene of the sn-2 aliphatic group of unsaturated molecular species of lysophosphatidylcholine. 

Disinfection. The disinfection efficiency of /V-ha1amines is related to the extent of hydrolysis to hypohalous acid. For example, NH2CI (Kf 10 ) is a poor bactericide compared to HOCl (5). By contrast, monochloroisocyanurate 10 ) exhibits good bactericidal properties (6). 

Although pH determines the ratio of hypohalous acid to hypohaUte ion, the fraction of the total available halogen present as HOX is dependent on of the halamine as well as the concentration of excess amine. In the case of chloroisocyanurates, which are the most widely used /V-ch1oramine disinfectants in swimming pools and spas, the extent of hydrolysis at 1 ppm av CI2 (as monochloroisocyanurate) is - 34% but only - 1% when 25 ppm cyanuric acid is added (4). Nevertheless, effective disinfection can stiU occur with chloroisocyanurates if a sufficient FAC is maintained, eg, 1—3 ppm. The observed reduction in disinfection rate because of cyanuric acid (6) has been shown to be direcdy related to the concentration of HOCl formed by hydrolysis of chloroisocyanurates (10). 

Preparation. Substituted A/-halamines are usually prepared by reaction of RR NH with halogen, hypohalous acid, or hypohaUte where R is an organic substituent and R is either an organic substituent or H. 

The critical intermediate (64) for this route (Scheme 65) can be reached in several ways. The commonest is by the reaction of an alkene with hypohalous acid (Scheme 66) which proceeds with overall retention. 

The manner and rate of decomposition of hypohalous acids (and hypohalite ions) in solution are much influenced by the concentration, pH and temperature of the solutions, by the presence or absence of salts which can act as catalysts, promotors or activators, and by light quanta. The main competing modes of decomposition are ... 

In addition to the applications indicated on p. 858. hypohalous acids are useful halogenating agents for Ixjth aromatic and aliphatic compounds. HOBr and HOI are usually generated in silii. The ease of aromatic halogenation increa.ses in the sequence OCl < OBr < Ol and is facilitated by salts of Pb or Ag. Another well-known reaction of hypohalites is their cleavage of methyl ketones to form carboxylates and haloform ... 

Yet another example of an electrophilic addition is the reaction of alkenes with the hypohalous acids HO—Cl or HO-Br to yield 1,2-halo alcohols, called halohydrins. Halohydrin formation doesn t take place by direct reaction of an alkene with HOBr or HOC1, however. Rather, the addition is done indirectly by reaction of the alkene with either Br2 or Cl2 in the presence of water. 

The acid strengths and oxidizing abilities of the halogen oxoacids increase with the oxidation number of the halogen. The hypohalous acids, HXO (halogen oxidation number +1), are prepared by direct reaction of the halogen with water. For example, chlorine gas disproportionates in water to produce hypochlorous acid and hydrochloric acid ... 

A procedure that is useful for the preparation of both bromohydrins and iodohy-drins involves in situ generation of the hypohalous acid from NaBr03 or NaI04 by reduction with bisulfite.43... 

Halogenating Agents In situ halide oxidation by mammalian white blood cells, fungi, and aquatic plants Stabilized Hypohalous Acids... 

Hypohalous acids, e.g. HO8-—Br8+ (bromine water), were thought to add on in very much the same way, but there is some evidence that the actual electrophile may well be the halogen itself, e.g. Br2, and that both 1,2-dibromide (35a) and 1,2-bromhydrin (35 b) are then obtained by competition of Br and H20 for the... 

Although solutions containing the hypohalous acids are produced by dissolving the halogens in water, the process must be carried out at low temperature. Hypohalites are also produced when halogens react in basic solution. 

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