Acyl nitroxides. Part 4. Estimation of OH bond dissociation energies for N-t-butylhydroxamic acids

Jenkins, Terence C.; Perkins, M. J.

doi:10.1039/p29830000717

Cited by 14 publications

(7 citation statements)

References 3 publications

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“…Although one might expect the BDE of (PhCO)( t -Bu)NOH to be larger than that of (CF 3 ) 2 NOH, the actual BDE of PhCON( t -Bu)OH (323 kJ mol -1 ) is smaller than that of (CF 3 ) 2 NOH (346 kJ mol -1 ), which is reflected in the difference of the rate constants for hydrogen abstraction reactions from toluene. Jenkins et al measured the π-spin density on oxygen in 17 O-labeled (PhCO)( t -Bu)NO• and found that 12% of the π-spin exists on the carbonyl oxygen. , We are not sure how much π-spin exits on the carbonyl oxygen of the PINO radical. However, the two acyl groups of PINO• would delocalize the nitrogen lone pair to a greater extent than on the (PhCO)( t -Bu)NO•.…”

Section: Resultsmentioning

confidence: 98%

“…Jenkins et al proposed that lone-pair delocalization from nitroxide nitrogen would tend to fix the unpaired electron on oxygen. 38 Therefore, if the two acyl groups of NHPI withdraw electron density from the nitrogen atom and fix the unpaired electron on an oxygen atom (N-O•), this would strengthen the O-H bond of NHPI. However, if the unpaired electron exists principally on the carbonyl oxygen (structure III), we also must consider the π-spin density on the oxygen.…”

Section: Rate Constants Versus C-h Bond Dissociation Energiesmentioning

confidence: 99%

“…Jenkins et al measured the π-spin density on oxygen in 17 O-labeled (PhCO)-(t-Bu)NO• and found that 12% of the π-spin exists on the carbonyl oxygen. 38,40 We are not sure how much π-spin exits on the carbonyl oxygen of the PINO radical. However, the two acyl groups of PINO• would delocalize the nitrogen lone pair to a greater extent than on the (PhCO)(t-Bu)NO•.…”

Section: Rate Constants Versus C-h Bond Dissociation Energiesmentioning

confidence: 99%

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Kinetic Study of the Phthalimide N-Oxyl (PINO) Radical in Acetic Acid. Hydrogen Abstraction from C−H Bonds and Evaluation of O−H Bond Dissociation Energy of N-Hydroxyphthalimide

2003

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The reactions of the phthalimide N-oxyl (PINO) radical with several hydrocarbons having different C−H bond dissociation energies (BDEs) were investigated in HOAc at 25 °C. The slope of the Evans−Polanyi plot is 0.38, which indicates that the reactions are mildly exothermic or almost thermoneutral. This finding is supported by the O−H BDE of N-hydroxyphthalimide (NHPI), 375 ± 10 kJ mol-1, obtained by means of a thermodynamic cycle. The observed kinetic isotope effects (KIEs) are related to the reaction free-energy changes, which can be explained by a Marcus-type equation. The comparison of the PINO radical reactions with analogous hydrogen atom abstraction reactions of the dibromide radical implies that HBr2• reactions are more exothermic than the PINO radical reactions. This factor is put forth to explain the different KIEs.

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Section: Resultsmentioning

confidence: 98%

Section: Rate Constants Versus C-h Bond Dissociation Energiesmentioning

confidence: 99%

Section: Rate Constants Versus C-h Bond Dissociation Energiesmentioning

confidence: 99%

See 1 more Smart Citation

Kinetic Study of the Phthalimide N-Oxyl (PINO) Radical in Acetic Acid. Hydrogen Abstraction from C−H Bonds and Evaluation of O−H Bond Dissociation Energy of N-Hydroxyphthalimide

2003

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“…As reported in [23], the acyl groups of NHPI withdraw electron density from nitrogen atom and fix the electron on an oxygen atom in N-O, making the O-H bond stronger. Indeed, NHPLI contains three electron-withdrawing carbonyl groups and have the stronger O-H bond (90.25 kcal/ mol).…”

Section: Nhplimentioning

confidence: 85%

Substituted N-hydroxyphthalimides as oxidation catalysts

Novikova¹,

Kompanets²,

Kushch³

et al. 2011

Reac Kinet Mech Cat

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A series of substituted N-hydroxyphthalimides (NHPI) with electronwithdrawing groups (4-C(O)OH, C=O) and an electron-donating group (4-C(CH 3 ) 3 ) were investigated as catalysts for cumene oxidation. The initial reaction rates, measured by the oxygen uptake, conversion of substrate and yield of oxidation products are discussed. The catalytic activity of oxidation rate enhancement of NHPI derivatives in acetonitrile follows the order 4-tert-BuNHPI [ NHPI [ 4-carb-NHPI [ NDHPI [ NAPI. NMPT, trityl-NPI and NHPLI are inactive.

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“…[13] [c] Ref. [16] asc.wiley-vch.de consisting of NHPI (10 mol %) and Co(acac) 2 , has been commercialized by the Daicel Chemical Company. The products are used in the manufacture of photoresistant polymers.…”

Section: ð2þmentioning

confidence: 99%

Organocatalytic Oxidations Mediated by Nitroxyl Radicals

2004

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The use of nitroxyl radicals, alone or in combination with transition metals, as catalysts in oxidation processes is reviewed from both a synthetic and a mechanistic viewpoint. Two extremes of reactivity can be distinguished: stable (persistent) dialkylnitroxyls, such as the archetypal TEMPO, and reactive diacylnitroxyls, derived from N-hydroxy imides, such as N-hydroxyphthalimide (NHPI). The different types of reactivity observed are rationalized by considering the bond dissociation energies (BDEs) of the respective N-hydroxy precursors, substrates and reaction intermediates. Reactive diacylnitroxyl radicals are generated in situ from the corresponding N-hydroxy compound. The protagonist, NHPI, catalyzes a wide variety of free radical autoxidations, improving both activities and selectivities by increasing the rate of chain propagation and/or decreasing the rate of chain termination. In the absence of metal co-catalysts improved conversions and selectivities are obtained in the autoxidation of hydrocarbons to the corresponding alkyl hydroperoxides. For example, cyclohexylbenzene afforded the 1-hydroperoxide in 97.6% selectivity at 32% conversion when the autoxidation was performed in the presence of 0.5 mol % NHPI, and the product hydroperoxide as initiator, at 100 8C. This forms the basis for a potential coproduct-free route from benzene to phenol. In combination with transition metal co-catalysts, notably cobalt, NHPI and related compounds, such as N-hydroxysaccharin NHS, afford effective catalytic systems for the effective autoxidation of hydrocarbons, e.g., toluenes to carboxylic acids, under mild conditions. In the case of the less reactive cycloalkanes, NHS proved to be a more active catalyst than NHPI which is attributed to the higher reactivity of the intermediate nitroxyl radical, resulting from the replacement of a carbonyl group in NHPI by the more strongly electron-attracting sulfonyl group. Stable dialkylnitroxyl radicals, exemplified by TEMPO, catalyze oxidations of, e.g., alcohols, with single oxygen donors such as hypochlorite and organic peracids. The reactions involve the intermediate formation of the corresponding oxoammonium cation as the active oxidant. Alternatively, in conjunction with transition metals, notably ruthenium and copper, they catalyze aerobic oxidations of alcohols. These reactions involve metal-centered dehydrogenations and the role of the TEMPO is to facilitate regeneration of the catalyst (Ru and Cu) and oxidation of the alcohol (Cu) via hydrogen abstraction or one-electron oxidation processes. Detailed mechanistic investigations, including kinetic isotope effects, revealed that oxoammonium cations are not involved as intermediates in these reactions. In contrast, oxoammonium cations are involved in the aerobic oxidation of alcohols catalyzed by the copper-dependent oxidase, laccase, in combination with TEMPO. This different mechanistic pathway is attributed to the much higher redox potential of the copper(II) in the enzyme. Similarly, N-hydroxy compounds such as ...

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Acyl nitroxides. Part 4. Estimation of OH bond dissociation energies for N-t-butylhydroxamic acids

Cited by 14 publications

References 3 publications

Kinetic Study of the Phthalimide N-Oxyl (PINO) Radical in Acetic Acid. Hydrogen Abstraction from C−H Bonds and Evaluation of O−H Bond Dissociation Energy of N-Hydroxyphthalimide

Kinetic Study of the Phthalimide N-Oxyl (PINO) Radical in Acetic Acid. Hydrogen Abstraction from C−H Bonds and Evaluation of O−H Bond Dissociation Energy of N-Hydroxyphthalimide

Substituted N-hydroxyphthalimides as oxidation catalysts

Organocatalytic Oxidations Mediated by Nitroxyl Radicals

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