Reactivities of diarylmethyl and triarylmethyl cations with primary amines in aqueous acetonitrile solutions. The importance of amine hydration

McClelland, Robert A.; Kanagasabapathy, V. M.; Banait, Narinder S.; Steenken, S.

doi:10.1021/ja00031a041

Cited by 89 publications

(70 citation statements)

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“…30,34, 35 Ratios of trifluoroethyl ethers to phenols from reactions in aqueous TFE and appreciable yields of fluoroarenes from reactions in TFE implicate a highly reactive, shortlived, and non-discriminating aryl cation intermediate. 30, 36 We conclude that simple arenediazonium ions in the polar solvents of our investigation decompose by the mechanism of Scheme 1 proposed previously.…”

Section: Discussionmentioning

confidence: 80%

Rates and mechanisms of the thermal solvolytic decomposition of arenediazonium ions

Canning¹,

McCrudden²,

Maskill³

et al. 1999

J. Chem. Soc., Perkin Trans. 2

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Arenediazonium tetrafluoroborates have been prepared and the kinetics of solvolysis have been investigated in water, trifluoroethanol, water-trifluoroethanol mixtures, hexafluoropropan-2-ol, trifluoroacetic acid, and ethanol by a UV method. A heterolytic mechanism involving short-lived aryl cations leads to products derived from nucleophilic capture of the aryl cations by solvent or a solute. Ionic solutes in aqueous trifluoroethanol and trifluoromethoxybenzene in trifluoroethanol have no kinetic effect and neither does replacement of the tetrafluoroborate counter-ion by chloride in trifluoroethanol. Rate constants for any one compound are not very solvent dependent, the reactions generally being characterised by high enthalpies of activation and appreciably positive entropies of activation. Compounds with 4-Cl, 4-F, 4-NO 2 , and 4-MeO substituents proved too unreactive for kinetic studies, but for different reasons. In ethanol, a radical reaction with characteristically different activation parameters competes with the heterolytic path and leads to hydrodediazoniation (reduction) by hydrogen atom abstraction from the CH 2 group of ethanol.

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Section: Discussionmentioning

confidence: 80%

Rates and mechanisms of the thermal solvolytic decomposition of arenediazonium ions

Canning¹,

McCrudden²,

Maskill³

et al. 1999

J. Chem. Soc., Perkin Trans. 2

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“…337), while pure verdazilium salt is quantitatively reduced to the radical (run nos. 10,11). Thus the degree of regeneration of triphenylverdazyl from products of reaction (2) by an alkaline solution of formaldehyde tends to decrease as the concentration of water in the solvent decreases.…”

Section: äääääääääääämentioning

confidence: 94%

“…1 Complete capture of that intermediate by triphenylverdazyl (at a typical concentration of 10 !4 M) requires the corresponding rate constant to be about 10 13 mol !1 s !1 . However, the diffusion limit for reactions of neutral amines with cationic species derived diphenylmethyl chloride in acetonitrile is 5 + 10 9 mol !1 s !1 [10]. Such values of rate constants are unprecedented for reactions involving outer-sphere electron transfer in nonstructurized systems.…”

Section: äääääääääääämentioning

confidence: 94%

Is Triphenylverdazyl an Indicator for Solvent-Separated Ion Pair?

et al. 2005

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The hypothesis implying complete capture of solvent-separated ion pairs by triphenylverdazyls used as internal indicators for unimolecular heterolysis of organic compounds was critically analyzed. Products of heterolysis of diphenylmethyl bromide in anhydrous acetonitrile in the presence of triphenylverdazyl were identified, and their distribution was determined. Alkylation of verdazyl under kinetic conditions almost does not occur, and verdazyl is consumed as a result of its reaction with hydrogen bromide liberated during the solvolysis.

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“…8 Plots of observed and computed log(k Q ) as functions of free energy change (DG el ) of electron transfer at the reaction distance, using the Agmon-Levine model constant for 4-methoxyacetphenone triplet quenching by several phenols is substantially reduced when the latter are hydrogen-bonded to a variety of substrates. Another example of the negative effect of H-bonding on reactivity is that observed on the electrophilic reaction of diarylmethyl and triarylmethyl cations with primary amines in aqueous acetonitrile [81]. The negative effect from water in this example has been attributed to formation of a hydrated amine, RNH 2 … HOH, which is, apparently unreactive (in contrast with free RNH 2 ).…”

Section: Phenolsmentioning

confidence: 94%

Quenching of diphenylmethyl radical fluorescence by cyanoaromatics and phenols

Cyr

Das

2015

Res Chem Intermed

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We have used double-laser nanosecond laser flash photolysis to study the kinetics of bimolecular quenching of the lowest doublet excited state of the transient diphenylmethyl radical ( 2 Ph 2 CH Á ) in acetonitrile at 25°C. We chose a series of cyanoaromatic compounds as acceptor-type quenchers and a series of 4-substituted phenols as donor-type quenchers. The observed bimolecular quenching rate constants (k Q ) are in the range 2 9 10 6 -2 9 10 10 M -1 s -1 for cyanoaromatics and 1 9 10 5 -3 9 10 9 M -1 s -1 for phenols. The Hammett plots of the k Q values for these two series have positive and negative slopes, respectively, and establish the enhanced behavior of the photo-excited diphenylmethyl radical as both a donor and an acceptor. For cyanoaromatics, the trend in the dependence of 2 Ph 2 CH Á * quenching rate constants on the free energy change of electron transfer (DG el ) coincides well with that of RehmWeller data on acceptor-type and donor-type quenchers of singlet excited states. An approximate fit of the k Q data for cyanoaromatics to the Agmon-Levine model of electron transfer gave a value of 4.5 kcal mol -1 for the free energy of activation at DG el = 0. For phenols, the trend in the dependence of k Q on the free energy change of electron transfer deviates significantly from that of cyanoaromatics data. This deviation was traced to the use of irreversible oxidation potentials of phenols to calculate DG el . No isotope effect is observed from substitution of phenolic hydrogen by deuterium, i.e., k Q,H /k Q,D & 1. Phenolate ions quench 2 Ph 2 CH Á * with large rate constants, 1-2 9 10 10 M -1 s -1 , i.e., well in the limit of diffusion control.

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Reactivities of diarylmethyl and triarylmethyl cations with primary amines in aqueous acetonitrile solutions. The importance of amine hydration

Cited by 89 publications

References 1 publication

Rates and mechanisms of the thermal solvolytic decomposition of arenediazonium ions

Rates and mechanisms of the thermal solvolytic decomposition of arenediazonium ions

Is Triphenylverdazyl an Indicator for Solvent-Separated Ion Pair?

Quenching of diphenylmethyl radical fluorescence by cyanoaromatics and phenols

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