Hypohalites Hypobromites, Hypochlorites

The homolysis of tertiary hypochlorites for the production of oxy radicals is well known." The ease with which secondary hypohalites decompose to ketones has hampered the application of hypohalites for transannular reactions. However the tendency for the base-catalyzed heterolytic decomposition decreases as one passes from hypochlorites to hypobromites tohypoidites. Therefore the suitability of hypohalites for functionalization at the angular positions in steroids should increase in the same order. Since hypoidites (or iodine) do not react readily with ketones or carbon-carbon double bonds under neutral conditions hypoiodite reactions are more generally applicable than hypochlorite or hypobromite decompositions. 

The most widely used, and often most convenient reagents for such one-pot reactions are sodium hypochlorite (45) or hypobromite (16). These reactions are performed in the presence of an organic base (generally triethylamine) that normally enhances the yield of cycloaddition products (45). This method was employed for many intermolecular reactions (71) and also seems especially suited for intramolecular ones (72-77) as well as for the solid-phase synthesis (78) of 2-isoxazolines. Hypohalite can also be replaced by sodium broruite in combination with a catalytic amount of tri-u-butyltin chloride (79). In a related method, O-tributylstannyl oximes were treated with tert-butyl hypochlorite to produce nitrile oxides that were trapped with aUcenes or alkynes to afford the corresponding isoxazolines or isoxazoles in moderate to good yield (80). 

Boron trifluoride and boron trifluoride-diethyl ether complex can be used as a source of fluoride ions in the presence of hypobromites and hypochlorites, e.g. methyl hypobromitc, tert-butyl hypobromite, methyl hypochlorite in carbon tetrachloride at 25 C. The addition of bromine monofluoride" and chlorine monofluoride" to various alkenes is accompanied by the formation of the corresponding alkoxybromides and alkoxychlorides which hinder the isolation of the halofluorinated products.57 jV-Bromo- and A -chloro-substiluted alkyl- and arylamines. -amides, and -imides, A -chloro-A,-methylamine, A -bromo-A -methylamine, A -chloro-A, /V-dimethylamine, A-bromo-A.A-dimethylamine, ACV-dichloro-A -methylamine, V,fV-dibromo-,V-mcthylaminc, A -bromosuccinimide, -V-chlorosuccinimide, Af-bromoacct-amide, A.A -dichlorourethane, can be used in the reaction instead of the hypohalites. The reactions with various alkenes conducted in dichloromethane at room temperature in the presence of boron trifluoride-diethyl ether complex produce bromofluoro and chlorofluoro addition products in 40-80 % yield. However, the reactions are complicated by the addition of A -halo-succinimides and Af.A-dichlorourcthane to the C = C bonds.58... 

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,... 

Alkoxy radicals produced by homolysis of hypohalites can attack non-activated C-H bonds, and lead to tetrahydro-furanoid structures after basic treatment of the intermediate halo-alcohols. Hypochlorites of [2y,2g] and C(20)-tertiary alcohols [28,2gJ gave 6 8,19- and 18,20-oxido derivatives respectively on irradiation and hydrolysis, but the more reactive hypobromites and hypoiodites are now preferred. Akhtar ef al. [30] distinguish between two modes of reaction of a 6jS-hypobromite (2), generated in situ by treating the alcohol with bromine and silver acetate. Experiments with... 

Reaction of hypochlorite with bromide and iodide leads to formation first of the other hypohalite and then, more slowly, of the halates. With bromide ion, between pH 10 and 14, formation of hypobromite is the only significant process , although the halates were detected at lower pH. The rate equation... 

It is known from Houben-Weyl, Methoden der organischen Chemie, volume 8, pages 415-416, that carboxylic acids can be manufactured by oxidation of methyl ketones with hypohalites in an aqueous medium. The publication recommends dispersing the ketone by means of oxidation-resistant emulsifiers or carrying out the reaction in the presence of dioxane all the examples were carried out in this way. In most cases the reaction only takes place satisfactorily with hypobromite solutions, which are more expensive and less stable than hypochlorite solutions. For this reason alone, industrial utilization of the reaction is confined to special reactions with aromatic ketones. 

Halogenation is also effected by acyl hypohalites, such as acetyl hypochlorite and trifluoroacetyl hypobromite. ... 

Hypohalites s. Acetyl hypo-bromite, Alkyl hypohalites, Hypochlorites, Potassium hypobromite. Sodium hypochlorite... 

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. 

Two pathways are detected in the copper(ii)-catalysed oxidation of hypochlorite and hypobromite (HOX) in basic solution to give X and molecular oxygen. An intermediate absorbing maximally at 362 and 270 nm arises from reaction of the copper dimer [Cu2(OH)7] with the hypohalite. Formation of the intermediate is suppressed in the presence of a large excess of Br but Cl has no comparable effect. The results are explained in terms of the equilibria... 

This reaction of hypohalites (hypochlorites and hypobromites) with luminol has since been used as an indicator in oxidative titrations by hypohalite of the following ions 8203 " W 8405 ... 

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