Hydroxylamine, oxime formation

Diels-Alder reaction of 2-bromoacrolein and 5-[(ben2yloxy)meth5i]cyclopentadiene in the presence of 5 mol % of the catalyst (35) afforded the adduct (36) in 83—85% yield, 95 5 exo/endo ratio, and greater than 96 4 enantioselectivity. Treatment of the aldehyde (36) with aqueous hydroxylamine, led to oxime formation and bromide solvolysis. Tosylation and elimination to the cyanohydrin followed by basic hydrolysis gave (24). 

Dimethyl ketals and enol ethers are stable to the conditions of oxime formation (hydroxylamine acetate or hydroxylamine hydrochloride-pyridine). Thioketals and hemithioketals are cleaved to the parent ketones by cadmium carbonate and mercuric chloride. Desulfurization of thioketals with Raney nickel leads to the corresponding methylene compounds, while thioenol ethers give the corresponding olefin. In contrast, desulfurization of hemithioketals regenerates the parent ketone. ... 

Amongst other N-nucleophilic species, hydroxylamine exhibits some abnormal behavior besides oxime formation (p. 25). Thus it reacts with diphenyl cyclopropenone42 probably by 1,4-addition and subsequent oxidation and/or decarboxylation giving rise to 3,4-diphenyl isoxazolone (328) and desoxybenzoin oxime. With pentyl cyclopropenone48 hydroxylamine undergoes addition followed by normal oxima-tfon after ring fission yielding 2,3-dioximino octane (329). 

The reduction of aliphatic nitrocompounds in acid solution proceeds in two steps. First the nitrosocompound is formed. A low steady state concen ation of 2-methyl-2-nitrosopropane has been detected during the reduction of 2-methyl-2-nitropropane [13]. At the cathode potential necessary to attach the first electron to a nitro group, the nitroso intermediate undergoes further reduction to the hydroxyla-mine. When the nitrocompound has one a-hydrogen substituent, tautomerism of the nitroso intermediate to an oxime is in competition with further reduction. Both temperature and proton availability affect the rate of this isomerisation. Reduction of aliphatic nitrocompounds to the hydroxylamine is usually carried out in acid solution at 0-5° C to minimise oxime formation [14, 15], The hydroxylamine is stable towards further reduction in acid solution. Oximes in acid solution are reduced... 

Organic thermochemistry of hydroxylamines, oximes, and hydroxamic acids 69 TABLE 3. Enthalpies of formation for dioximes (kJ mol )... 

Deprotection of polystyrene-bound ketimines has been achieved by treatment with aqueous HC1 or TFA in THF [260,313], or by benzophenone oxime formation with hydroxylamine hydrochloride [314,315] (Figure 10.17). 

Conditions for effecting this conversion in one step have been described.65 The method involves heating a mixture of the aldehyde, hydroxylamine hydrochloride, sodium formate and formic acid and the reaction is considered to proceed through the intermediate formation of an oxime formate. 

N-Oxidation. (V-oxidation can occur in a number of ways, including hydroxylamine formation, oxime formation, and N-oxide formation, although the latter is primarily dependent on the FMO enzyme. Hydroxylamine formation occurs with a number of amines such as aniline and many of its substituted derivatives. In the case of 2-acetylaminofluorene the product is a potent carcinogen, and thus the reaction is an activation reaction (Figure 7.6). 

Oxime formation from cyclohexanone with hydroxylamine, and... 

Oxime Formation from Cyclohexanone with Hydroxylamine... 

Oxime formation with cyclohexanone takes place with a hydroxylamine salt (either sulfate or phosphate) at 85°C46 ... 

With hydroxylamine, however, strong alkali has an accelerating effect upon oxime formation while it does not upon semicarbazone forma-... 

Aldehydes, particularly aromatic aldehydes, when refluxed in formic acid with a slight excess of hydroxylamine hydrochloride and sodium formate are converted into nitriles.15 Probably the oxime formate (2) is an intermediate and in the presence... 

Amide formation. Redox reaction between aldehydes and hydroxylamine leads to carboxamides. The reaction, catalyzed by Rh(OH)n in water at 160°, perhaps proceeds via oxime formation, dehydration and rehydration. 

N-Acylanilines. When electron-rich arenes are treated with a carboxylic acid, hydroxylamine hydrochloride in PPA, several reactions occur in sequence. These are the Friedel-Crafts acylation, oxime formation, and Beckmann rearrangement. Anilides are obtained in 45-95% overall yields (11 examples). 

Tollen s test, described previously, can be used to distinguish between the aldehyde and -the ether. Also, oxime formation with hydroxylamine, and Schiff test with the fuchsin-aldehyde reagent to fom a characteristic magenta color can be used. 

Oxime formation proceeds at a ketone by a standard addition-elimination mechanism with hydroxylamine and elimination of water. 

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