Kinetic substituent and isotope effects in the acid-catalysed rearrangement of N-phenylhydroxylamines. Are nitrenium lons involved?

Kohnstam, G.; Petch, W. Andrew; Williams, D. Lyn H.

doi:10.1039/p29840000423

Cited by 33 publications

(26 citation statements)

References 6 publications

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“…Product identifications were verified by spiking the reaction mixtures with authentic samples. Rate constants were measured as previously described (7)(8)(9), by following the change in optical density at an appropriate wavelength in the UV.…”

Section: Methodsmentioning

confidence: 99%

“…This same study also showed that there was no exchange of 180 into unreacted starting material, establishing that N-0 bond fission is not reversible (5) (although a similar study with N-1-naphthylhydroxylamine (6) suggests that this is not always the case). Detailed kinetic studies showed that the reaction was first order in phenylhydroxylamine and first order in H+ to pH 1-2, with the rate then becoming independent of acidity to acids with Ho of about -1, at which point the rate began to increase again (7)(8)(9). Spectral measurements suggested that the initial levelling was associated with protona?con to the unreactive N-protonated hydroxylamine 7, with p~a N = 1.90 for the parent system (7,9).…”

mentioning

confidence: 96%

“…This, however, proved not to be possible since the acidities required for sufficient free azide ion to be present (pH > 4) were too low for the Bamberger rearrangement to occur at a significant rate. In this case, significant quantities of oxidation products are formed even with rigorous dearation (7,9) and these complicate the analysis. One approach we considered was to move to a phenylhydroxylamine derivative where the phenylnitrenium ion forms by simple ionization, as has been done by the Novak group (21)(22)(23).…”

Section: Nhoh Nhoh Nhohmentioning

confidence: 99%

“…Spectral measurements suggested that the initial levelling was associated with protona?con to the unreactive N-protonated hydroxylamine 7, with p~a N = 1.90 for the parent system (7,9). The acid catalysis at higher acidities was explained by a mechanism involving a diprotonated intermediate PhN+H20+H2 (7, lo), although a medium or salt effect could not be ruled out (9).…”

mentioning

confidence: 99%

“…Detailed kinetic studies showed that the reaction was first order in phenylhydroxylamine and first order in H+ to pH 1-2, with the rate then becoming independent of acidity to acids with Ho of about -1, at which point the rate began to increase again (7)(8)(9). Spectral measurements suggested that the initial levelling was associated with protona?con to the unreactive N-protonated hydroxylamine 7, with p~a N = 1.90 for the parent system (7,9). The acid catalysis at higher acidities was explained by a mechanism involving a diprotonated intermediate PhN+H20+H2 (7, lo), although a medium or salt effect could not be ruled out (9).…”

mentioning

confidence: 99%

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Halide ion trapping of nitrenium ions formed in the Bamberger rearrangement of N-arylhydroxylamines. Lifetime of the parent phenylnitrenium ion in water

Fishbein¹,

McClelland²

1996

Can. J. Chem.

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The acid reactions of five arylhydroxylamines (Ar = 2,6-Me2C6H3, 2,5-Me2C6H3, 2-MeC6H4, 2-C1C6H4, and C6H5) have been studied at constant ionic strength (NaC104) in the presence of varying amounts of NaBr and NaCI. Each system resulted in the corresponding p-aminophenol, the product of Bamberger rearrangement, as the only detectable product in the absence of halide. ' The addition of halide ion reduced the yield of this product, with the appearance of the corresponding p-haloaniline, o-haloaniline (where appropriate), and the parent aniline (predominantly with bromide). Rate constants for the reaction were measured in the case of the parent and 2,6-dimethyl systems and showed small decreases (chloride) or increases (bromide) with increasing halide concentration. These changes did not correlate with the change in products, implying that the rate variations were caused by specific salt effects. Product data were analyzed by a mechanism involving rate-limiting formation of the appropriate arylnitrenium ion followed by product-determining steps involving trapping by the solvent or by the added halide. The possibility that a portion of the halide-trapped products were derived from a pre-association mechanism was also included. Kinetic analyses then produced kBr:kw and kcl:kw ratios for two limiting cases, one involving pre-association with an equilibrium constant K,, = 0.3, and one ignoring pre-association. From an azide:water ratio (kAz:kw) previously determined for the 2,6-dimethylphenylnitrenium, kBr was concluded to lie in the range (4-5) x lo9 M-I s-I for all of the nitrenium ions of this study. This range for kB, then led to k, values of (1-2) x lo9 s-I (2.5-Me2), (2-3) x 10' s-' (2-Me), and (4-8) x lo9 s-' (parent and 2-Cl), where the ranges reflect uncertainties in the exact value of kBr and in the contribution from pre-association. The lifetime of the parent phenylnitrenium ion in water at one molar ionic strength is concluded to lie in the range 125-250 ps.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 96%

Section: Nhoh Nhoh Nhohmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Halide ion trapping of nitrenium ions formed in the Bamberger rearrangement of N-arylhydroxylamines. Lifetime of the parent phenylnitrenium ion in water

Fishbein¹,

McClelland²

1996

Can. J. Chem.

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Syn andanti aryl nitrenium ions

1999

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Bamberger Rearrangement

2010

Comprehensive Organic Name Reactions and Reagents

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Intermolecular rearrangement of N ‐phenylhydroxylamines in acidic aqueous solution to afford the corresponding 4‐aminophenols, e.g., in aqueous sulfuric acid, is generally referred to as the Bamberger rearrangement. It has been reported that in this rearrangement the hydroxyl group is introduced into the aromatic ring via a nucleophilic attack of a hydrosulfate ion on the anilenium ion, which is generated by the heterolytic N‐O bond cleavage of O ‐protonated N ‐phenylhydroxylamine. It has been found that alkoxy, halogen, phenoxy are incorporated into the aromatic ring when the rearrangement of N‐phenylhydroxylamine is carried out in nucleophilic solvents.

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Kinetic substituent and isotope effects in the acid-catalysed rearrangement of N-phenylhydroxylamines. Are nitrenium lons involved?

Cited by 33 publications

References 6 publications

Halide ion trapping of nitrenium ions formed in the Bamberger rearrangement of N-arylhydroxylamines. Lifetime of the parent phenylnitrenium ion in water

Halide ion trapping of nitrenium ions formed in the Bamberger rearrangement of N-arylhydroxylamines. Lifetime of the parent phenylnitrenium ion in water

Syn andanti aryl nitrenium ions

Bamberger Rearrangement

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