Hypohalite solutions

Hofmann Reaction.72 In contrast to the molecular rearrangements which have been discussed, the Hofmann reaction proceeds in an alkaline medium. In this reaction an amide is treated with a hypohalite solution, and, under the usual conditions of the reaction, an amine with one less carbon atom is obtained ... 

Gaseous alkynes are passed into alkaline (up to 23% referred to KOH) hypo-halite solution at 0°. Liquid alkynes or solutions of solid ones in light petroleum are shaken or stirred with the hypohalite solution at room temperature, sometimes with addition of an emulsifier. The necessary hypohalite solutions are prepared as follows 432... 

Alkali cleaves, a ,a>trihalomethyl ketones to trihalomethanes and carboxylic acids. This haloform reaction 714 also occurs directly if alkaline hypohalite solution is allowed to react with a methyl ketone and has preparative importance as a method of obtaining carboxylic acids from methyl ketones. 

The reaction is generally carried out by warming the amide in aqueous hypohalite solution rapidly to about 70°. Allen and Wolf give the following directions in Organic Syntheses119 for conversion of nicotinamide into 3-pyri-dinamine ... 

In certain cases arterial prostheses of poly(ether-urethanes) have been halogenated by allowing the hypohalite solution to flow through them for a short time (e.g. 2 minutes). The depth of penetration of halogenation was assessed by use of a scanning electron microscope with a EDAX attachment. 

The Hofmann reaction generally is carried out by dissolving the amide in a very slight excess of cold aqueous hypohalite solution, followed by rapid warming (with steam distillation if the amine produced is volatile). A valuable modification (p. 282) consists in carrying out the reaction in an alcoholic (usually methanolic) solution, with subsequent hydrolysis of the urethan so obtained. 

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. 

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". 

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... 

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. 

However, if the solutions are hot, the hypohalites undergo disproportionation to produce X()3 and X-. 

Halogenoalkynes are also formed from alkynes and aqueous solutions of hypohalites. In these reactions, alkynylide anions are transient intermediates. The conversions give good results only when the acetylene has a low pK (e.g. aryl-feCH and ROCCsCH) or good solubility in water (e.g..HC-CCXCHj OH) [122], The hypohalite method of Strauss [123] has most applications in the synthesis of bromoacetylenes. 

The traditional method of oxidizing hydrazine derivatives makes use of halogens or hypohalites as oxidizing agents. The techniques range from the preparation of l,l -azobis(l-cyclohexanenitrile) by the addition of bromine to an alcoholic hydrochloric acid solution of the corresponding hydrazine [89], through the use of bromine water [90, 91] to oxidations with sodium hypo-bromite [64] or sodium hypochlorite [92]. 

In runs for obtaining analytical data, the hypohalite and BF3 OEl2 were added to a 0.3 M solution of the alkene in CH2C1, at rt. The amount of hypohalite was sufficient to consume 20% of the alkene and was in a 1 1 molar ratio to the BFV... 

The anion of this acid results from the oxidation of red phosphorus wiih hypohalites in alkaline solution ... 

The finely divided metal is soluble in hypohalites if an excess of alkali is present. At red heat, the metal combines with C z to form the dichlondc. Ruthenium(VIIl) oxide is formed when an alkaline ruthenium solution is treated with a strong oxidant, such as chlorine, or bromate ion when the Ru is in acid solution,... 

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). 

Hypochlorites.—The starting-point for these compounds is the hypohalite it is produced by the action of a hydroxide on the element in cold aqueous solution, thus ... 

Chlorine and bromine add vigorously, giving, with proper control, high yields of 1,2-dihaloethyl ethers. In the presence of an alcohol, halogens add as hypohalites, which give 2-haloacetals. With methanol and iodine, this is used as a method of quantitative analysis by titrating unconsumed iodine with standard thiosulfate solution. 

A-Haloamides and imides are a most versatile group of halogenating reagents. They are normally prepared in an aqueous solution by reaction of the parent amide/imide with the corresponding hypohalite. An improved method for the synthesis of A-bromo amides/imides has recently been published, in which the parent compounds are oxy-brominated in aqueous solution by a mixture of HBr/NaBr03 or NaBr/NaBr03/H2S04 (equation 95)700. 

The reaction above is reversible, for if the colorless basic solution is acidified, the elementary halogen is regenerated. Hypohalites will not survive in warm solution, but undergo further self-oxidation or dis-mutation. Typically, the OBr ion is converted to BrOi" and Br it follows, therefore, that basic hydrolysis of bromine results ultimately in bromide and bromate ions in about a 5 1 ratio ... 

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,... 

Benzidine acetate test (DANGER THE REAGENT IS CARCINOGENIC) A neutral or weakly acetic acid solution of a peroxodisulphate converts benzidine into a blue oxidation product. Perborates, percarbonates, and hydrogen peroxide do not react. Chromates, hexacyanoferrate(III) ions, permanganates, and hypohalites react similarly to peroxodisulphates. 

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

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