Hypohalite ions

Hypohalite ion Hypohalite ions Hypohalous acid Hypokalemia... 

Since hypohalous acid is a much more active disinfectant than the hypohalite ion, the effect of pH on ionization becomes important. Hypobromous acid has a lower ionization value than hypochlorous acid and this contributes to the higher disinfectant activity of BrCl compared with chlorine. 

ForCb, Bt2 and h, K. c is 4.2 x 10- 7.2 x 10 and 2.0 x 10 mol 1 respectively, thereby favouring the free halogens, whereas Kaik is 7.5 X lO, 2 X lO and 30mol I respectively, indicating a tendency to disproportionation which is overwhelming for CI2 but progressively less pronounced for Br2 and I2. In actuality the situation is somewhat more complicated because of the tendency of the hypohalite ions themselves to disproportionate further to produce the corresponding halite ions ... 

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 ... 

Hypohalite ions, XO, are formed when a halogen is added to the aqueous solution of a base. Sodium hypochlorite, NaClO, is produced from the electrolysis of brine when the electrolyte is rapidly stirred, and the chlorine gas produced at the... 

Among the numerous mediator systems, halide ions show the broadest applicability. The internal electrochemical generation of the active species, i.e., molecular halogen, hypohalite ions, and halonium ions, is always possible by the in-cell method without... 

Hypohalite ions reaction with ozone [OZONE] (Vol 17)... 

The oxidation with halogens and hypohalites is a complicated reaction, as it depends strongly on the conditions of temperature, acidity, and concentration of the reacting species. The halogens show considerable differences in the positions of the various equilibria and the speed with which the equilibria are attained (see Table I). In acidic solution, the equilibrium between free halogen and hypohalous acid [Eq. (7. )] lies far to the left, and the concentration of hypohalous acid is very low. When alkali is added to the system, the concentration of hypohalite ion increases, according to Eq. (14). 

The hypohalite ions, OCl, OBr, and OI, are formed (along with equivalent quantities of the corresponding halide ions) when the elemental halogens are hydrolyzed in basic solution. Two solid hypobromites and several solid hypochlorites have been isolated. The so-called bleaching powder or chloride of lime, prepared by treatment of calcium hydroxide with chlorine, is often described as a mixed salt Ca(OCl)Cl (however,... 

The hypoiodite ion is much less stable than the other hypohalite ions, decomposing almost completely to iodate and iodide in a few hours, whereas the corresponding decomposition of hypochlorite at the same concentration and the same temperature requires several years. 

The hypohalite ions can all be produced in principle by dissolving the halogens in cold base according to the general reaction... 

The situation, however, is complicated by the tendency of the hypohalite ions to disproportionate further in basic solution to produce the halate ions ... 

For this reaction the equilibrium constant is in each case very favorable, that is, 1027 for CIO", 1015 for BrO", and 1020 for IO". Thus the actual products obtained on dissolving the halogens in base depend on the rates at which the hypohalite ions initially produced undergo disproportionation, and these rates vary from one to the other and with temperature. 

In the Hofmann reaction (Scheme 8.2), an amide is treated with a halogen, usually bromine, in alkali in which the reactive species is the hypohalite ion (XO ). This reaction, which applies to aliphatic as well as aromatic amides, has been thoroughly studied. Evidence supporting... 

Other vanadium-containing enzymes appear to be particularly important the production of polybrominated compounds in the sea (8, 70). The va-idium peroxidases utilize hydrogen peroxide to oxidize bromide or iodide, obably to corresponding hypohalite ions, which then react with NOM to oduce polyhalogenated compounds (eq 17) (8, 70). 

Hydrogen peroxide is a substrate for myeloperoxidase, a multisubunit heme protein of M.W. 150,C, present in primary neutrophilic granules. The active prosthetic groups are two hemes covalently attached to the apoen-zyme. This enzyme catalyzes many kinds of oxidation reactions, but oxidation of halide ions to hypohalite ions appears to be the most important. Hypochlorite ion is the principal compound formed, although Br , I, and SCN (a pseudohalide) can also serve as substrates. The reaction catalyzed is... 

Oxidation of some sulphides, with either chromate249 or permanganate250-252, leads to low yields of sulphonic acids as exemplified in equation 39. Hypohalite ions or nitric acid may also be used for this transformation5, as shown in equations 40 and 41. In both cases the yields are rather low. 

The mechanism by which hypohalites oxidize alcohols probably involves initial formation of an alkyl hypohalite (Eq. 16.16). This product arises from reaction of the alcohol with the hypohalous acid that is in equilibrium with hypohalite ion in aqueous medium (Eq. 16.15). Base-promoted E2 elimination of the elements of H-X from the alkyl hypochlorite leads directly to either an aldehyde or ketone. The advantage of using hypohalite as an oxidant is immediately obvious upon examining Equation 16.16. The inorganic by-product derived from the oxidant is a halide salt that can be safely flushed down the drain. Reactions that do not produce toxic by-products are environmentally friendly and are now commonly referred to as "Green Chemistry." (See the Historical Highlight at the end of this chapter.)... 

When alkali is added to the system, the concentration of hypohalite ion increases ... 

Oxidation with Hypohalites in Alkaline Solutions. In alkaline solution the halogens exist as hypohalous acid and hypohalite ions. The oxidation is likely to be more drastic than for the free halogens. Thus, whereas free iodine will not act as an oxidant, hypoiodite is a powerful oxidizing agent. Hypobromite and hypochlorite particularly are likely to produce oxidation of primary and secondary alcoholic groups and cause cleavage of carbon-carbon bonds. As noted above, the processes are complicated by the tendency of hypohalite to be converted to halate ions. 

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