Hydroxylamine, oxime formation with

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). 

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

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. 

The intermediate iminium salts can also be transformed into functional groups other than carbonyls. Three common variants are quenching with hydrogen sulfide to yields thioaldehydes (13- 14), oxime formation with hydroxylamine followed by dehydration to yield nitriles (15—>16), and hydride reduction to yield dialkylamines (17—>18). ... 

Hydroxylamine is known to be highly toxic to plants so the possibility that it is an obligatory intermediate in nitrate reduction must be considered with caution. Interest in hydroxylamine arises from the lengthy controversy, briefly mentioned here, concerning the rela-j five merits of hydroxylamine or ammonia as the key intermediate in nitrogen fixation. The toxicity of hydroxylamine may well be due to its action as an enzyme inhibitor. However, in spite of its toxicity, there are still some claims that hydroxylamine may be an intermediate in the formation of amino acids by oxime formation with such carbonyl compounds as glyoxilic acid (formed in photosynthesis), I pyruvate, a-ketoglutarate or oxaloacetate (intermediates in carbo-... 

The hydroxylamine method in which the mineral acid, liberated from hydroxylamine salts by oxime formation with the aldehyde, is titrated direct, requires to be modified according to the particular aldehyde or ketone being determined (Bennett and Cocking" ). The advantages of the hydroxylamine process over the absorption methods given above are recognised as (a) the hydroxylamine method is a definite determination of aldehydic or ketonic substances, whereas the absorption methods include impurities such as water-soluble organic acids and adulterants such as alcohol (d) a small quantity only of the oil is required and the determination can be completed in a much shorter time. Yet it must be pointed out... 

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... 

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... 

The reaction of 2-acetyl-3-hydroxypyridine (441) with hydroxylamine 0-sulfonic acid afforded a 1 1 mixture of compound (442) and 2-methylisoxazolo[4,5-6]pyridine (443) (Equation (35)) <87H(26)292i). The formation of the oxazolo[4,5-6]pyridine (442) results from a Beckmann rearrangement. The reaction of the oxime (444) with hydroxylamine O-sulfonic acid also gave Beckmann rearrangement products, such as (445) and (446) as a 1 1 mixture (Equation (36)). 

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... 

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). 

The ammoximation of cyclohexanone to cyclohexanone oxime (Scheme 9.1) is an important industrial process, because the oxime is an intermediate for the formation of s-caprolactam, the monomer for nylon-6, that is currently manufactured on a scale of 4 Mton p.a. TS-1 catalyses the ammoximation of ketones, including cyclohexanone, in liquid phase in the presence of ammonia and hydrogen peroxide. The reaction proceeds through hydroxylamine as an intermediate, which is generated at the active site via complexes of framework titanium with ammonia and hydroperoxide. The hydroxylamine then reacts with cyclohexanone molecules that are weakly adsorbed within the pores or can diffuse out into solution. The reaction is a general one, and can be apphed to the ammoximation of a wide range of ketones. 

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

Similarly, Friedel-Crafis acylation (Chapter 6 cf. Scheme 6.88) of aromatic systems produces carbonyl compounds, which can be converted to the corresponding oximes with hydroxylamine hydrochloride (H2NOH-HC1) (see, e.g.. Scheme 9.65, Table 9.4, item 4). So, acylation of benzene to form phenylethanone (acetophenone, methylphenylketone, C6H5COCH3) can be followed by oxime formation. 

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