Hypohalites

Preliminary results suggest direct oxidation of oxo(per-oxo)vanadium(V) ion by hypochlorous acid, -d[0V02]/df = 6.5 X 10 [OVO2lHOCI], although this equation does not hold accurately over the entire course of a kinetic run. 

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The reaction is applicable to the preparation of amines from amides of aliphatic aromatic, aryl-aliphatic and heterocyclic acids. A further example is given in Section IV,170 in connexion with the preparation of anthranilic acid from phthal-imide. It may be mentioned that for aliphatic monoamides containing more than eight carbon atoms aqueous alkaline hypohalite gives poor yields of the amines. Good results are obtained by treatment of the amide (C > 8) in methanol with sodium methoxide and bromine, followed by hydrolysis of the resulting N-alkyl methyl carbamate ... 

This reaction illustrates the conversion of the —COCH3 group into the —COOH group by means of a hypohalite ... 

The main example presented will be the alkaline-hypohalite method as it is the easiest to acquire the necessary chemicals. It Is of interest to note that the alkaline-halide method is much easier to perform, process- wise, in that it is more forgiving of sloppy technique. 

The general theory behind the process is that the hypohalite will convert the amide to a haloamide. This then spontaneously changes to the isocyanate when heated and decomposes to the amine from the water present. In effect, all that happens is that a Carbonyl (CO) group is stripped off the starting amide to yield the corresponding amine. Yields pre- purification are around 80%, post-purification average around 65%. Certain uses of the result-... 

Hypohalite ion Hypohalite ions Hypohalous acid Hypokalemia... 

Ghlorohydrination with er -All l Hypohalites. Olefins react with ethyl hypochlorite [624-85-1] to form the corresponding chlorohydrin (49). In 1938 both Shell Development Co. (50) and Arthur D. Litde, Inc. (51) patented the preparation of chlorohydrins by the reactions of olefins with tertiary alkyl hypochlorites. Examples with ethylene and propylene in the Shell patent reported chlorohydrin yields of greater than 95% with tert-huty hypochlorite [507-40-4]. 

Oxirane and chlorine allegedly form complexes C2H4O Cl and C2H4O 3C1 (64HC(19-1)445) at -80 C, but in this and other cases explosions occurred at room temperature, perhaps caused by hypohalites. 

The latter is an exttemely reactive species. Trifluoroacetate is a good leaving group and facilitates cleavage of the O—Br bond. The acyl hypohalites are also the active halogenating species in solutions of the hypohalous acids in carboxylic acids, where they exist in equilibrium. 

O-X Alkyl perchlorates. Chlorite salts. Halogen oxides, Hypohalites, Perchloric acid, Perchloryl Compounds... 

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. 

In most cases the carbon radical formed in the hydrogen abstraction step 2 will react with the radical R formed in the homolysis of the X—R bond. However, a cage reaction does not seem to be involved in this step. This has been established in the nitrite photolysis and probably applies to hypohalites as well. In the lead tetraacetate reaction, the steps following the oxyradical formation leading to tetrahydrofuran derivatives are less clear. 

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 primary product of hypohalite photolysis is a 1,5-halohydrin, the stability of which increases on passing from iodo- to bromo- to chloro-hydrins. If spontaneous elimination of hydrogen halide does not occur, the halohydrins can be converted into tetrahydrofurans by base treatment. In several instances it has been possible to isolate the intermediate... 

Tnorganic and perfluoroorganic hypohalites add across olefimc bonds (equation 11 andTable 1) Thereactionsofhypofluontes have been included in a review on their chemistry [2J], In reactions of perfluoorganic hypofluontes, considerable fluonnation of the C=C bond may be observed With hypochlorites such as... 

Other oxoacid salts of the alkali metals are discussed in later chapters, e.g. borates (p. 205), silicates (p. 347), phosphites and phosphates (p. 510), sulfites, hydrogensulfates, thiosulfates, etc. (p. 706) selenites, selenates, tellurites and tellurates (p. 781), hypohalites, halites, halates and perhalates (p. 853), etc. 

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 ... 

Solutions of the corresponding hypohalites can be made by the rapid disproportionation of the individual halogens in cold alkaline solutions (p. 856) ... 

Such solutions are necessarily contaminated with halide ions and with the products of any subsequent decomposition of the hypohalite anions themselves. Alternative routes are the electrochemical oxidation of halides in cold dilute solutions or the chemical oxidation of bromides and iodides ... 

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 ... 

The acids decompose more readily than the anions so hypohalites are stabilized in basic solutions. The stability of the anions diminishes in the sequence CIO" > BrO" > lO". 

Other uses of hypohalous acids and hypohalites are described in the Panel. 

This section concludes with a reminder that, in addition to the hypohalous acids HOX and metal hypohalites M(OX) , various covalent (molecular) hypohalites are known. Hypochlorites are summarized in Table 17.22. All are volatile liquids or gases at room temperature and are discussed elsewhere (see Index). Organic hypohalites are unstable and rapidly expel HX or RX to form the corresponding aldehyde or ketone ... 

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 ... 

The Gassman indole synthesis involves an one-pot process in which hypohalite, a P-carbonyl sulfide derivative 2, and a base are added sequentially to an aniline or a substituted aniline 1 to provide 3-thioalkoxyindoles 3. Raney nickel-mediated desulfurization of 3 then produces the parent indole... 

Cycloalkoxy radical intermediates are readily generated from a parent alcohol by various methods (e.g., nitrite ester photolysis, hypohalite thermolysis, lead tetraacetate oxidation) (83MI1). Once formed, reactive cycloalkoxy radicals undergo /3-scission to produce a carbonyl compound and a new carbon-centered radical. 

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... 

The first step is not a free-radical process, and its actual mechanism is not known. Compound 30 is an acyl hypohalite and is presumed to be an intermediate, though it has never been isolated from the reaction mixture. Among the evidence for the mechanism is that optical activity at R is lost (except when a neighboring bromine atom is present, see p. 899) if R is neopentyl, there is no rearrangement, which would certainly happen with a carbocation and the side products, notably RR, are consistent with a free-radical mechanism. There is evidence that the Simonini... 

Addition of Hypohalous Acids and Hypohalites (Addition of Halogen, Oxygen)... 

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