3174-48-9Relevant academic research and scientific papers
Direct Irradiation of Phenol and Para-Substituted Phenols with a Laser Pulse (266 nm) in Homogeneous and Micro-heterogeneous Media. A Time-Resolved Spectroscopy Study
Siano, Gastón,Crespi, Stefano,Bonesi, Sergio M.
, p. 14012 - 14025 (2020/11/20)
Direct irradiation of para-substituted phenols under N2 atmosphere in homogeneous (cyclohexane, acetonitrile, and methanol) and micellar (SDS) solution was investigated by means of time-resolved spectroscopy. After a laser pulse (266 nm), two transient species were formed, viz. the para-substituted phenol radical-cations and the corresponding phenoxy radicals. The radical-cations showed a broad absorption band located between 390 and 460 nm, while the phenoxy radicals showed two characteristic bands centered at 320 nm and 400-410 nm. The deprotonation rate constant of radical-cations (kH) of 105 s-1 and the reaction rate constant of the phenoxy radicals (kR) in the order of 109-1010 M-1·s-1 have been derived. The kH rate constants gave good linear Hammett correlation with positive slope indicating that electron-withdrawing substituents enhance the radical-cation acidity. The binding constants (Kb) of the para-substituted phenols with the surfactant were also measured, and NOESY experiments showed that phenols were located in the hydrophobic core of the micelle. Finally, computational calculations provided the predicted absorption spectra of the transients and nice linear correlations were obtained between the theoretical and experimental energy of the lower absorption band of these species.
Hydrogen hyperfine splitting constants for phenoxyl radicals by DFT methods: Regression analysis unravels hydrogen bonding effects
Amorati, Riccardo,Pedulli, Gian Franco,Guerra, Maurizio
body text, p. 3136 - 3141 (2010/08/21)
DFT calculations using the B3LYP functional, medium-sized basis sets and empirical scaling of the results provide quantitative estimates of the hydrogen isotropic hyperfine splitting constants (hscs) in 2,6-di-alkyl phenoxyl radicals (1-11). Literature hs
Oxidation of phenols employing polyoxometalates as biomimetic models of the activity of phenoloxidase enzymes
Galli, Carlo,Gentili, Patrizia,Nunes Pontes, Ana Sofia,Gamelas, Jose A. F.,Evtuguin, Dmitry V.
, p. 1461 - 1467 (2008/02/13)
A kinetic study of the oxidation of substituted phenols with either vanadium(v) polyoxotungstate, [α-SiVVW11O 40]5- (viz. SiW11V), or manganese(iii) polyoxotungstate, [α-SiMnIIIW11/su
Synthesis and inhibitory activity of alkyl(hydroxyaryl)amines
Dyubchenko,Nikulina,Terakh,Prosenko,Grigor'ev
, p. 1149 - 1155 (2008/09/17)
The reaction of ω-(4-hydroxyaryl)haloalkanes with various nitrogen-containing agents afforded primary, secondary, and tertiary amino derivatives of 2,6-dialkylphenols. For the compounds synthesized, the reaction rate constants with peroxide radicals were
Bimolecular hydrogen abstraction from phenols by aromatic ketone triplets
Lathioor, Edward C.,Leigh, William J.
, p. 291 - 300 (2008/02/05)
Absolute rate constants for hydrogen abstraction from 4-methylphenol (para-cresol) by the lowest triplet states of 24 aromatic ketones have been determined in acetonitrile solution at 23°C, and the results combined with previously reported data for roughly a dozen other compounds under identical conditions. The ketones studied include various ring-substituted benzophenones and acetophenones, α,α,α-trifluoroacetophenone and its 4-methoxy analog, 2-benzoylthiophene, 2-acetonaphthone, and various other polycyclic aromatic ketones such as fluorenone, xanthone and thioxanthone, and encompass n,π*, π,π*(CT) and arenoid π,π* lowest triplets with (triplet) reduction potentials (Ered*) varying from about -10 to -38 kcal mol-1. The 4-methylphenoxyl radical is observed as the product of triplet quenching in almost every case, along with the corresponding hemipinacol radical in most instances. Hammett plots for the acetophenones and benzophenones are quite different, but plots of log log kQ vs Ered* reveal a common behavior for most of the compounds studied. The results are consistent with reaction via two mechanisms: a simple electron-transfer mechanism, which applies to the n,π* triplet ketones and those π,π* triplets that possess particularly low reduction potentials, and a coupled electron-/proton-transfer mechanism involving the intermediacy of a hydrogen-bonded exciplex, which applies to the π,π* ketone triplets. Ketones with lowest charge-transfer π,π* states exhibit rate constants that vary only slightly with triplet reduction potential over the full range investigated; this is due to the compensating effect of substituents on triplet state basicity and reduction potential, which both play a role in quenching by the hydrogen-bonded exciplex mechanism. Ketones with arenoid π,π* states exhibit the fall-off in rate constant that is typical of photoinduced electron transfer reactions, but it occurs at a much higher potential than would be normally expected due to the effects of hydrogen-bonding on the rate of electron-transfer within the exciplex.
Abnormal solvent effects on hydrogen atom abstractions. 1. The reactions of phenols with 2,2-diphenyl-1-picrylhydrazyl (dpph?) in alcohols
Litwinienko, Grzegorz,Ingold
, p. 3433 - 3438 (2007/10/03)
Rate constants, kArOH/dpph?,s, for hydrogen atom abstraction from 13 hindered and nonhindered phenols by the diphenylpicrylhydrazyl radical, dpph?, have been determined in n-heptane and a number of alcoholic and nonalcoholic, hydrogen-bond accepting solvents. Abnormally enhanced values of kArOH/dpph?,s have been observed in alcohols. It is proposed that this is due to partial ionization of the phenols and a very fast electron transfer from phenoxide anion to dpph?. The popular assessment of the antioxidant activities of phenols with dpph? in alcohol solvents will generally lead to an overestimation of their activities.
Free electron transfer from several phenols to radical cations of non-polar solvents
Ganapathi,Hermann,Naumov,Brede
, p. 4947 - 4955 (2007/10/03)
Electron-transfer reactions from phenols to parent radical cations of solvents were studied using pulse radiolysis. Phenols bearing electron-withdrawing, electron-donating and bulky substituents were investigated in non-polar solvents such as cyclohexane, n-dodecane, n-butyl chloride and 1,2-dichloroethane. The experiments revealed the direct, synchronous formation of phenoxyl radicals and phenol radical cations in all cases and in nearly the same relative amounts. This was explained by two competing electron-transfer channels which depend on the geometry of encounter between the parent solvent radical cations and the solute phenol molecules. The mechanism is analysed at a microscopic level, treating diffusion as a slow process and the local electron transfer as an extremely rapid event. Furthermore, the effect of various phenol substituents and solvent types on the electron-transfer mechanism and on the decay kinetics of the solute phenol radical cations was analysed. The results were further substantiated using a quantum chemical approach.
Reactivity of substituted phenols toward alkyl radicals
Franchi, Paola,Lucarini, Marco,Pedulli, Gian Franco,Valgimigli, Luca,Lunelli, Bruno
, p. 507 - 514 (2007/10/03)
The rate constants for the reaction of primary alkyl radicals with substituted phenolic compounds have been measured in benzene or toluene at room temperature by using the radical clock technique. With three representative phenols, containing in the ortho positions substituents of different size, the kinetics of the hydrogen transfer to alkyl radicals was studied at different temperatures to obtain the corresponding Arrhenius parameters. The kinetic solvent effect on the reaction with α-tocopherol was also investigated in six different solvents behaving as hydrogen bond acceptors, while the reaction with 2,4,6-trimethylphenol and 2,6-di-tert-butylphenol was studied in toluene and γ-valerolactone. For some phenols, the effect of self-aggregation on the kinetic parameters was also studied.
Effect of Solvation on the Bond Dissociation Energies of Phenolic Antioxidants
Pedrielli, Pamela,Pedulli, Gian Franco
, p. 509 - 512 (2007/10/03)
The effect of solvent on the bond dissociation energies (BDEs) of the oxygen-hydrogen bond in substituted phenolic antioxidants has been investigated by means of an EPR technique.On changing the solvent from benzene to tert-butanol the BDE's were found to increase by ca. 2.2 kcal/mol for phenols without ortho substituents, by ca. 1 kcal/mol for 2,6-dimethyl substituted phenols while in 2,6-di-tert-butyl phenols they seem to be substantially unaffected.This behaviour has been interpreted by admitting that the BDE increase observed in tert-butanol is essentially due to the solvation of the hydroxylic hydrogen which stabilises the phenol, leaving the energy of the phenoxyl radical unaltered.Thus, solvation effects are expected to be large with unhindered phenols and relatively unimportant in phenols containing bulky substituents in the proximity of the OH group.
Photoinduced hydrogen abstraction from phenols by aromatic ketones. A new mechanism for hydrogen abstraction by carbonyl n,π* and π,π,* triplets
Leigh, William J.,Lathioor, Edward C.,St. Pierre, Michael J.
, p. 12339 - 12348 (2007/10/03)
Nanosecond laser flash photolysis studies have been carried out of the kinetics of inter- and intramolecular phenolic hydrogen abstraction by alkoxyacetophenone, 5-alkoxyindanone, and 4-alkoxybenzophenone triplets in acetonitrile and benzene solution. Information on the geometric requirements for abstraction by carbonyl and π,π,* triplets is derived from the results for a series.of ketones which contain a para-phenolic moiety attached via a para-oxyethyl linkage. For all of these compounds, the deuterium kinetic isotope effect on the triplet lifetime in acetonitrile solution indicates that triplet decay is determined by the rate of intramolecular abstraction of the remote phenolic hydrogen, which yields the corresponding phenoxyl-hemipinacol biradical. The biradicals have also been detected, and are about an order of magnitude longer-lived than the triplet in each case. For three of the compounds, the rates of the intramolecular process follow the same trend as that observed in the rates of bimolecular quenching of the parent methoxy-substituted ketones by p-cresol. Deviation from this trend is observed for the alkoxyindanone derivative, where an in-plane approach of the phenolic hydrogen to the carbonyl n-orbital is not possible. The trends in the rate constants for bimolecular quenching of a series of substituted benzophenones by p-cresol indicate that for n,π,* triplet abstractions, the quenching mechanism is different for electron donor-substituted and electron acceptor-substituted ketones: For π,π,* triplets and donor-substituted (n,π,* triplet) benzophenones, abstraction is proposed to occur by a mechanism involving the intermediacy.of a hydrogen-bonded exciplex, which yields the corresponding radicals by sequential electron- and proton-transfer. The rate constant for quenching by this mechanism thus depends mainly on the basicity of the ketone triplet state and the oxidation potential of the phenol.
