Other hypohalite reactions

Reaction of chlorine dioxide with hypochlorous acid is not stoichiometrically simple. At a pH of about 5.5, A[C102] A[HC10] and it is suggested that reaction (2) contributed as well as (1), viz. 

In agreement with this proposal is the observation that in acidic solution, the decomposition of CIO2 does not form any chlorate . The reproducibility of the data on the reaction was somewhat unsatisfactory. It was confirmed that chlorate (and chlorite) are formed at pH 6.95 The rate expression is  

Reaction rates of CIO2 with chlorine have been calculated from Bray s measurements on the reverse reaction. Bray showed that the rate of the corresponding reaction with iodine is small and decreases with acid concentration. He proposed that the process involved HIO as reactant. 

Decomposition of mixtures of hypochlorite and hypobromite leads to formation of both chlorate and bromate . The unravelling of the rate expressions and mechanism will require development of more selective analytical procedures than those used so far, although rate coefficients and tentative mechanisms have been reported. 

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 

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Electrophilic fluorination by substitution of hydrogen at unactivated tertiary carbon has been achieved by use of either CF3OF or elementary fluorine (diluted with N2). Electron-attracting substituents direct the reaction to remote C—H bonds, suggesting that the reaction has electrophilic rather than free-radical character. Examples include the 9a-fluorination of 5a-androstane-3/8,17/8-diol esters (309), 14a-fluorination of various 5a,6j8-dichloro-3,17-disubstituted steroids of type (310), and 17a-fluorination of 5a-cholestan-3j8-yl esters or their 5a,6/8-dichloro-derivatives. Hypobromite and other hypohalite reactions for the functionalization of unactivated carbon atoms are reviewed. ... 

A convenient procedure for the oxidation of primary and secondary alcohols was reported by Anelli and co-workers (8,9). The oxidation was carried out in CH2CI2 with an aqueous buffer at pH 8.5-9.5 utilizing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 1) as the catalyst and KBr as a co-catalyst. The terminal oxidant in this system was NaOCl. The major disadvantage of using sodium hypochlorite or any other hypohalite as a stoichiometric oxidant is that for each mole of alcohol oxidized during the reaction one mole of halogenated salt is formed. Furthermore,... 

Protoadamantanone has been prepared by the nitrous acid deamination of 2-amino-l-adamantanol (77%), by aprotic diazo-tization of endo-7-aminomethylbicyclo[3.3.1]nonan-3-one in benzene with an equivalent amount of acetic acid (67%), and by thermolysis of 1-adamantyl hypohalites followed by base-promoted cyclization of the resulting halo ketones (32-37%)." In spite of low and erratic yields, the last reaction sequence has provided the most convenient route to the protoadamantanes, since the other two approaches require lengthy syntheses of the starting materials. 

Other alkyl hypohalites usually add to carbon-carbon multiple bonds in a free-radical process.155-158 Ionic additions may be promoted by oxygen, BF3, or B(OMe)3.156-160 While the BF3-catalyzed reaction of alkyl hypochlorites and hypo-bromites gives mainly halofluorides,159 haloethers are formed in good yields but nonstereoselectively under other ionic conditions.156-158 160 In contrast, tert-BuOI reacts with alkenes in the presence of a catalytic amount of BF3 to produce 2-iodoethers.161 Since the addition is stereoselective, this suggests the participation of a symmetric iodonium ion intermediate without the involvement of carbocationic intermediates. 

Two explosions were encountered in reactions involving the hypofluorite. See other HALOGEN OXIDES, HYPOHALITES, IODINE COMPOUNDS... 

Concerning hypohalites, CTFE seems very efficient in contrast to other fluoro-alkenes which have led to monoadduct mainly. The reaction is as follows ... 

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. 

This picture has been broadly validated, and in some respects refined, by other work in which coal was depolymerized by acid-catalyzed transalkylation [as by interaction of coal with phenol and BF3 (23-27)] or by similar, less clearly defined, phenolation reactions (28-31), or selectively degraded by specific oxidants, such as dichromates (32-34), hypohalites (35-38), or peroxy-acids (39-43). But these studies have also revealed some previously unsuspected features. Buffer-controlled oxidation with Na2Cr207 (34) and KMn04 (44) have indicated an occasionally significant presence of straight-chain (up to C21) and branched-chain (up to C8) aliphatic compounds in coal. Oxidation with performic acid (41-43) has yielded substituted compounds that are clearly related to the microbial or chemical degradation products of lignin or flavonoids. And when applied to supposedly very similar coals, virtually identical depolymerization or oxidation procedures often furnished distinctly different product slates (45). 

Even though oxygen in small percentages catalyzes the reaction effectively, many other initiators have been disclosed, including peroxy compounds, ozonides, azo compounds, azines, amine oxides, oximes, hydrazines, and hypohalites. The pol3Tnerization reaction is highly exothermic and requires strict control and elaborate safety measures in order to prevent... 

The same reaction with chlorine or bromine, on the other hand, produces a halide and a hypohalite ... 

Problem 9.3. The following experimental observations have been made with respect to the representation of the h oform reaction shown in Scheme 9.9 and other such base-catalyzed haloform processes (a) the rate of disappearance of starting ketone is independent of both the concentration and nature (Cl, Br, or I) of the hypohalite used, and (b) as long as the solution remains basic and there is sufficient halogen present, the reaction will continue until all of the starting ketone is consumed. Formulate a rate expression for what you believe to be the rate-determining step in Scheme 9.9 and that is consonant with the observations. 

Haloform reactions are generally performed with halogens in the presence of hydroxide [251] or directly with hypohalites [252]. Alternative methods affording carboxylic acids from methyl ketones (or other enolizable substrates) include the aerobic oxidation in the presence of a catalytic amount of dinitrobenzene [253] with a base in a dipolar aprotic solvent such as DMF [254] or HMPT (hexamethylphospho-ric triamide) [255, 256] and the use of stoichiometric quantities of hypervalent iodide derivatives [95, 257] or nitrosylpentacyanoferrate [258]. Furthermore, metal catalysts can be used, and systems such as tert-butyl hydroperoxide in the presence of rhenium oxide [259], oxygen in combination with a copper complex [260], heteropolyacids [261] and Mn"/Co" systems [262] were found to be applicable. Finally, aryl ketones are selectively oxidized to aliphatic carboxylic acids by treatment with periodate [81] in the presence of ruthenium trichloride [263]. 

Many chemiluminescence reactions are oxidation reactions in the direct sense of the word they require an oxidant such as molecular oxygen, hydrogen peroxide, other peroxides, hypohalites etc. In some cases at least, singlet oxygen is apparently involved in chemiluminescence in the so-called Trautz-Schorigin reaction (p. 50) and in autoxidation reactions of hydrocarbons, carbonyl deriva-... 

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