Energetics of Cresols and of Methylphenoxyl Radicals

Richard, Laurence S.; Bernardes, Carlos E. S.; Diogo, Hermı́nio P.; Leal, João Paulo; Piedade, Manuel E. Minas da

doi:10.1021/jp073515m

Cited by 25 publications

(18 citation statements)

References 62 publications

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“…This observation contrasts with the behavior of other ferrociphenols and is certainly due to the steric constraints imposed by the two methyl ortho substituents 23. 24 Therefore, considering the more acidic character of cresols/resorcinols versus phenols,20 the intrinsic acidity of 3 , enhanced in its cation radical—which is a boundary mesomeric structure of the ferrocenium cation 3 . + (Scheme )23—should play the major role in the energetics and kinetics of this base‐promoted oxidation sequence.…”

Section: Resultsmentioning

confidence: 87%

“…In this respect, the radical cations of cresols and resorcinols are known to be more easily formed and more acidic than their phenol analogues 19. For example, a recent calorimetric study established that the enthalpy of formation of o ‐methylphenoxyl radicals has a value approximately 40 kJ mol −1 more negative than that of phenoxyl radicals 20. These considerations prompted us to undertake a stepwise determination of the oxidation pathway of 3 using different electrochemical methods and EPR spectroscopy, with comparison to its close analogues 1 and 2 .…”

Section: Introductionmentioning

confidence: 99%

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Deciphering the Activation Sequence of Ferrociphenol Anticancer Drug Candidates

Messina¹,

Labbé²,

Buriez³

et al. 2012

Chemistry A European J

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The complete oxidation sequence of a model for ferrociphenols, a new class of anticancer drug candidate, is reported. Cyclic voltammetry was used to monitor the formation of oxidation intermediates on different timescales, thereby allowing the electrochemical characterization of both the short-lived and stable species obtained from the successive electron-transfer and deprotonation steps. The electrochemical preparation of the ferrocenium intermediate enabled a stepwise voltammetric determination of the stable oxidation compounds obtained upon addition of a base as well as the electron stoichiometry observed for the overall oxidation process. A mechanism has been established from the electrochemical data, which involves a base-promoted intramolecular electron transfer between the phenol and the ferrocenium cation. The resulting species is further oxidized then deprotonated to yield a stable quinone methide. To further characterize the transient species successively formed during the two-electron oxidation of the ferrociphenol to its quinone methide, EPR was used to monitor the fate of the paramagnetic species generated upon addition of imidazole to the electrogenerated ferrocenium. The study revealed the passage from an iron-centered to a carbon-centered radical, which is then oxidized to yield the quinone methide, namely, the species that interacts with proteins and so forth under biological conditions.

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Section: Resultsmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Deciphering the Activation Sequence of Ferrociphenol Anticancer Drug Candidates

Messina¹,

Labbé²,

Buriez³

et al. 2012

Chemistry A European J

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show abstract

“…These data, together with the ⌬ ac G 0 values from Table 2, are depicted in Figure 3. The acidity trend in the methylphenols can be better understood with Figure 4, which displays the stabilities of the neutral phenols and their phenoxides, as measured by their enthalpies of formation [19].…”

Section: Mass Spectrometrymentioning

confidence: 99%

“…A zero value was assigned to the enthalpy of formation of the most stable isomer. The enthalpies of formation of the phenoxides were obtained from the enthalpies of formation of the parent phenols (reference [19]) and the corresponding acidities (see text).…”

Section: Mass Spectrometrymentioning

confidence: 99%

Determination of gas-phase acidities of dimethylphenols: Combined experimental and theoretical study

Madeira

Costa

Fernandez

et al. 2008

J. Am. Soc. Mass Spectrom.

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“…Cresols themselves are critical reagents in many organic syntheses and in a large number of industrial applications. [36][37][38][39][40][41][42][43][44][45] Much of their behavior is well understood, and thus they are used as model systems in studies ranging from catalysis to ionic liquids. While a wealth of information exists on cresols, including our own work on methylphenoxide anions and methylphenoxyl radicals, 46 methylenephenoxides are not yet well understood and present an opportunity to study distonic radical anions and diradicals by way of photodetachment.…”

mentioning

confidence: 99%