Hydroxylamine rearrangement

For example, the chloramine LV failed to rearrange when heated with base, a condition not unfavorable for the non-chain radical mechanism.812 Yet the corresponding hydroxylamine rearranged with phosphorus pentachloride in ether.813... 

In the reaction of dimethylfoimamide chloride with the imidoyl cyanide (299 equation 160) the amidine (300) is formed. Isoxazolines, prepared from amide chlorides and hydroxylamine, rearrange on heating or irradiation to give 2-aminoazirine (301 Scheme 46). Azirines (302) can also be prepared by treating chloroenamines with base and sodium azide. ... 

A variety of compounds can be obtained from this single electroreduction reaction. For example, the formation of the hydroxylamine (XIV) occurs at a platinum cathode (low hydrogen overpotential) in dilute aqueous acid. It is interesting to note that in aqueous sulfuric acid the hydroxylamine rearranges to yield p-aminophenol (XIX). 

Benzaldehyde reacts with hydroxylamine in the presence of excess of sodium hydroxide to 3deld an oxime of low m.p. (a- or. gjM-benzaldoxime) which is stable to alkah, but is rapidly rearranged by acids to give an isomeric oxime of higha m.p. ( 3- or < i/r-benzaldoxlme) ... 

Rearrangement, Aliphatic amine oxides without an ahphatic hydrogen atom P to the nitrogen undergo Meisenheimer s rearrangement when heated to give trisubstituted hydroxylamines. 

Allyl or benzyl groups on the nitrogen facilitate the process. The rearrangement appears to be intramolecular (13), proceeding by a cycHc mechanism as in the case of /V-2-buteny1-/V-metby1 aniline oxide giving /V-methyl-0-1-methylallyl-/V-phenyl-hydroxylamine. 

Electrolytic reductions generally caimot compete economically with chemical reductions of nitro compounds to amines, but they have been appHed in some specific reactions, such as the preparation of aminophenols (qv) from aromatic nitro compounds. For example, in the presence of sulfuric acid, cathodic reduction of aromatic nitro compounds with a free para-position leads to -aminophenol [123-30-8] hy rearrangement of the intermediate N-phenyl-hydroxylamine [100-65-2] (61). 

If primary or secondary amines are used, A/-substituted amides are formed. This reaction is called aminolysis. Hydra2ines yield the corresponding hydra2ides, which can then be treated with nitrous acid to form the a2ides used in the Curtius rearrangement. Hydroxylamines give hydroxamic acids. 

The treatment of 3-acylisoxazoles (438) with hydroxylamine hydrochloride gives furazan ketones (439). On the other hand, furazan ketones (439) rearrange to 3-acylisoxazoles (438) with a loss of hydroxylamine under the influence of a mineral acid. Thus, by refluxing phenacylphenylfurazan with concentrated alcoholic hydrogen chloride, 3-benzoyl-5-phenyl-isoxazole is formed similarly, phenyl(phenacylphenyl)furazan gives 3-benzoyl-3,5-diphenyl-isoxazole (62HC(17)1, p. 35). 

The conversion of cyclohexanone to cyclohexanone oxime is brought about by the use of hydroxylamine sulphate. The sulphuric acid is neutralised with ammonia to ammonium sulphate and this is separated from the oxime. In the presence of oleum the oxime undergoes the process known as the Beckmann rearrangement to yield the crude caprolactam. After further neutralisation with ammonia the caprolactam and further ammonium sulphate are separated by solvent extraction (Figure 18.7). 

Preparation of the oxime presents no problem, since there is little tendency for hydroxylamine to add to the double bond of the unsaturated system. A variety of acid catalysts has been used e.g., POCI3, BF3, p-ACNHC6H4SO2CI) to effect the rearrangement, and phosphorous oxychloride is the usual choice. 

Nucleophiles like alcohols [2, S], hydrogen sulfide [2], thiols [2,10], ammonia, amines, hydrazines, hydroxylamines [2 11, 12, 13, 14, 75], azides [2], other pseudohalides [2], phosphonates [2,16,17,18,19, 20], and phosphanes [2,19] add rapidly across the CO or CN double bond to yield stable adducts The phosphonate adduets undergo a subsequent aleohol—lester rearrangement [19, 20] (equation 2)... 

The mononuclear heterocyclic rearrangement (MHR) of isoxazole-3-amidoxime 108 in the presence of a base and hydroxylamine with concomitant removal of the amide moiety affords furazan acetaldoxime 109 (Scheme 56) (91CHE651, 91KGS827). 

Substituents R, R at the starting oxime 1 can be H, alkyl, or aryl. The reaction conditions for the Beckmann rearrangement often are quite drastic (e.g. concentrated sulfuric acid at 120 °C), which generally limits the scope to less sensitive substrates. The required oxime can be easily prepared from the respective aldehyde or ketone and hydroxylamine. 

Phenylhydroxylamine rearranges in sulfuric acid to give mainly p-aminophenol. Industrial routes to this compound have been developed in which phenylhydroxylamine, formed by hydrogenation of nitrobenzene in sulfuric acid over platinum-on-carbon, is rearranged as it is formed. Conditions are adjusted so that the rate of rearran ment is high relative to the rate of hydrogenation of hydroxylamine to aniline (15,17,86). An easy way to obtain a favorable rate ratio is to carry out the reduction with about 1% DMSO present in the sulfuric acid (79,81). 

C-Nitroso compounds with an a-hydrogen atom rearrange readily to the corresponding oxime (/7y) and perhaps to the unsaturated hydroxylamine 145). Reduction of these is discussed in the chapter on oximes. 

Aryl hydroxylamines treated with acids rearrange to aminophenols. Although this reaction (known as the Bamberger rearrangement) is similar in appearance to... 

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