Addition of hydroxylamine to cyclohexanone and bicyclic ketones. Steric, electronic and hydrogen bonding effects on the general mechanism of addition of amines to carbonyl compounds

Brighente, Inês Maria Costa; Vottero, L. R.; Terezani, Alberto Jose; Yunes, Rosendo A.

doi:10.1002/poc.610040207

Cited by 11 publications

(3 citation statements)

References 36 publications

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“…We tentatively assign this to different protonation states of the redox couple in the two media, leading to a different mechanism for the redox reaction. The p K a of phenylhydroxylamine is 1.96 and, although a somewhat different value might be expected for hydroxyaminophenyl groups in the film, it is likely that a significant fraction are protonated in the strongly acidic medium, and deprotonated in base.…”

Section: Figurementioning

confidence: 88%

Reduction of Nitrophenyl Films in Aqueous Solutions: How Many Electrons?

et al. 2016

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The surface concentration of nitrophenyl (NP) films is commonly calculated from the charge associated with its redox reactions in aqueous solution. Reduction is usually carried out in acidic or basic solution and is assumed to proceed by either four electrons, or a mixed four and six electron process. Here, we reproducibly graft NP films of different thicknesses to glassy carbon electrodes from the corresponding diazonium ion and examine the reduction of the films in strongly acidic and basic solutions. We demonstrate that in most, if not all, cases, assumption of a four‐electron reduction of NP groups coupled with use of the redox reaction of the hydroxylamine product will lead to an underestimation of the surface concentration of NP groups. Use of acidic media with the assumption of a mixed four and six electron reduction of NP groups is shown to be an electrochemically and chemically sensible approach to estimating surface concentrations of NP groups.

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Section: Figurementioning

confidence: 88%

Reduction of Nitrophenyl Films in Aqueous Solutions: How Many Electrons?

et al. 2016

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“…The aqueous solution of H 2 SO 4 is the key for obtaining high selectivity to the 4-aminophenol. The success is due to the easy protonation of the phenylhydroxylamine (pk a = 1.9 [10]), which is extracted from the organic phase. In the acid solution (H 2 SO 4 concentration 0.6-1 mol L −1 ), the sulfate of the N-phenylhydroxylamine is formed and it undergoes fast rearrangement to the corresponding 4-aminophenol salt [11].…”

Section: Introductionmentioning

confidence: 99%

New insight on the mechanism of the catalytic hydrogenation of nitrobenzene to 4-aminophenol in CH3CN–H2O–CF3COOH as a reusable solvent system. Hydrogenation of nitrobenzene catalyzed by precious metals supported on carbon

Quartarone

Ronchin

Tosetto

et al. 2014

Applied Catalysis A: General

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a b s t r a c tThe preparation of 4-aminophenol via hydrogenation of nitrobenzene in a single liquid phase has been carried in the presence of different precious metal catalysts. The liquid phase is composed of CH 3 CN-H 2 O-CF 3 COOH, which can be easily distilled at low temperature, thus avoiding work-up operation. The yield of 4-aminophenol is in the range 45% and in the presence of sulfolane as promoter reaches almost 50%. The best result has been obtained in the presence of Pt/C as hydrogenation catalyst. The role of the solvent is strictly related to the selectivity to 4-aminophenol, since CH 3 CN decreases the hydrogenation activity compared to other solvent, CF 3 COOH promotes the formation of the desired product both via Bamberger rearrangement in solution as well by a surface catalyzed reaction, while H 2 O is responsible for 4-aminophenol formation in both reactions. Even though, nitrosobenzene and phenylhydroxylamine have not been observed, their reactivity suggest a complex pattern of reactions occurring either on the catalyst surface or in the solution. Indeed, formation of 4-aminophenol may occur both in solution, via acid catalyzed Bamberger rearrangement and on the catalyst surface by the formation of a surface Pt-nitrenium complex, which undergoes surface nucleophilic attack by H 2 O.

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“…As has been established in previous works, 10 the value of k3 for the reaction of hydroxylamine with norcamphor is not diffusion-controlled, and logically the same behaviour is expected for the reaction of N-methylhydroxylamine and norcamphor. As the value k3 could be different for both amines, we take into consideration the line that passes through the two points giving a slope of 0.60, and this slope is greater than the slope of least-squares line for the bases that exhibit the "concerted" mechanism (k1) of value 0.42 (r = 0.96).…”

Section: Resultsmentioning

confidence: 65%

The general mechanisms of attack of nitrogen nucleophiles on carbonyl compounds: facts that determine the change of the rate-pH profiles

Brighente¹,

Yunes²

1997

J. Braz. Chem. Soc.

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Foi descrito um mecanismo geral para a etapa de ataque da reação de nucleófilos nitrogenados com compostos carbonílicos para formar intermediários de adição neutro. Este mecansimo geral está baseado na importância relativa do mecanismo "concertado" com respeito ao mecanismo "por etapas". O mecanismo "concertado" envolve o ataque da base nitrogenada ao composto carbonílico catalisado pelo íon hidrônio, enquanto que o mecanismo "por etapas" envolve a formação prévia de um intermediário tetraédrico zwiteriônico (T ± ), com posterior transferência de próton a partir do íon hidrônio. A importância relativa destes dois passos origina três diferentes tipos de perfis de velocidade em função do pH. A importância do mecanismo "por etapas" depende da estabilidade do intermediário T ± , que por sua vez depende do pKa do nucleófilo nitrogenado e da constante de equilíbrio (Kad) para a formação do intermediário neutro (T 0 ). A comparação entre as reações de p-clorobenzaldeído e norcanfor com diferentes nucleófilos nitrogenados mostra que o mecanismo geral depende de cada tipo de composto carbonílico. Isto deve-se a dois fatos: A grande influência dos efeitos estéricos e eletrônicos na estrutura dos compostos carbonílicos, e o fato de que o valor do pKa do nucleófilo nitrogenado é o fator mais importante na predição dos perfis. O pKa do nucleófilo nitrogenado está mais relacionado com a estabilidade do intermediário T ± que de T 0 , enquanto que o valor de Kad está relacionado apenas com a estabilidade do intermediário T 0 .It have been described a general mechanism for the attack step of the reactions between nitrogen nucleophiles and carbonyl compounds to form a neutral tetrahedral addition intermediate. This general mechanism is based on the relative importance of the "concerted" hydronium-ion catalyzed attack of the nitrogen base on the carbonyl compound with respect to the "step wise" mechanism that involves the previous formation of a zwitterionic tetrahedral intermediate (T ± ) and the posterior proton transfer to it from the hydronium-ion. The relative importance of this pathway gives origin to three kinds of profile rates vs pH for these reactions. On the other hand, the importance of the "stepwise" mechanism was attributed to a dependence on the stability of the T ± intermediate that is related to the pKa of the nitrogen base and the Kad (the equilibrium constant for the formation of the neutral tetrahedral addition intermediate (T 0 )). The comparison of the reactions of p-chlorobenzaldehyde and norcamphor with different nitrogen nucleophiles led to the observation that the general mechanism depends on each type of carbonyl compound. This is due to the great influence of the steric and electronic effects of the compound's structure, and the fact that the pKa value of the nitrogen base, which is more related to the stability of the T ± than the T 0 intermediate, is more important as a factor of prediction of the profiles than the value of Kad, this value being more related to the stability of the T 0 intermediate.

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Addition of hydroxylamine to cyclohexanone and bicyclic ketones. Steric, electronic and hydrogen bonding effects on the general mechanism of addition of amines to carbonyl compounds

Cited by 11 publications

References 36 publications

Reduction of Nitrophenyl Films in Aqueous Solutions: How Many Electrons?

Reduction of Nitrophenyl Films in Aqueous Solutions: How Many Electrons?

New insight on the mechanism of the catalytic hydrogenation of nitrobenzene to 4-aminophenol in CH3CN–H2O–CF3COOH as a reusable solvent system. Hydrogenation of nitrobenzene catalyzed by precious metals supported on carbon

The general mechanisms of attack of nitrogen nucleophiles on carbonyl compounds: facts that determine the change of the rate-pH profiles

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