54560-44-0Relevant academic research and scientific papers
Phenolic hydrogen abstraction by the triplet excited state of thiochromanone: A laser flash photolysis study
Ribeiro, Alessandra M.,Bertoti, Ada Ruth,Netto-Ferreira, Jose? Carlos
scheme or table, p. 1071 - 1076 (2010/10/21)
Triplet ketones are known to oxidize biological substrates which can lead to damage of several biomolecules such as amino acids, nucleosides and DNA. As part of our systematic study on the interaction between carbonyl compounds and phenols, the triplet reactivity of thiochromanone (1) towards substituted phenols, in acetonitrile, was investigated employing the laser fash photolysis technique. The quenching rate constants ranged from (1.1 ± 0.1) × 108 L mol-1 s-1 (4-cyanophenol) to (5.8 ± 1.0) × 109 L mol-1 s-1 (hydroquinone). A Hammett plot for the reaction of triplet 1 with phenols containing polar substituents resulted in a reaction constant ρ =-0.90. This negative value observed for the reaction constant ρ is in accord with a mechanism in which the hydrogen transfer from phenols to the triplet carbonyl involves a coupled electron/proton transfer.
Kinetic solvent effects on hydrogen-atom abstractions: Reliable, quantitative predictions via a single empirical equation
Snelgrove,Lusztyk,Banks,Mulder,Ingold
, p. 469 - 477 (2007/10/03)
The rate of hydrogen-atom abstraction from XH by a radical, Y·, can be solvent-dependent. In many cases, the kinetic solvent effect (KSE) is directly related to hydrogen-bonding interactions between XH and the solvent. The relative hydrogen-bond acceptor (HBA) properties of solvents are given by β2/H constants of Abraham et al. (Abraham, M. H.; Grellier, P. L.; Prior, D. V.; Morris, J. J.; Taylor, P. J. J. Chem. Soc. Perkin Trans. 2 1990, 521-529). Room-temperature rate constants for hydrogen-atom abstraction, kXH/Y·/S, have been determined in a number of solvents, S, where XH refers to several substituted phenols, tert-butyl hydroperoxide or aniline and Y· is a tert-alkoxyl radical. In all cases, plots of log(kXH/Y·/S/M-1 s-1) versus β2/H gave excellent linear correlations, the slopes of which, MXH, were found to be proportional to the hydrogen-bond-donating (HBD)ability of XH, as scaled with α2/H parameters of Abraham et al. (Abraham, M. H.; Grellier, P. L.; Prior, D. V.; Duce, P. P.; Morris, J. L.; Taylor, P. J. J. Chem. Soc., Perkin Trans. 2 1989, 699-711), with MXH = - 8.3α2/H. This leads to a general empirical equation which quantifies KSEs at room temperature: log kXH/Y·/S = log kXH/Y·O - 8.3α2/Hβ2/H, where kXH/Y·/O refers to the rate constant in a non-HBA solvent for which β2/H = 0, generally a saturated hydrocarbon. Since MXH depends only on XH, rate constants for hydrogen-atom abstraction from XH by any Y· can be accurately predicted in any of the several hundred solvents for which β2/H is known on the basis of one single measured rate constant, provided α2/H for XH is known or measured. HBA solvents can have profound effects on some of the reactions and thermodynamic properties of hydroxylic substrates including: (i) reaction product profiles (ii) antioxidant activities, (iii) Hammett-type correlations, and (iv) O-H bond dissociation enthalpies. Finally, literature data (Nielsen, M. F.; Hammerich, O. Acta Chem. Scand, 1992, 46, 883-896) on KSEs for two proton-transfer reactions are shown to be correlated by the same equation which correlates KSEs for hydrogen-atom transfers.
Effect of Ring Substitution on the Photochemistry of α-(Aryloxy)acetophenones
Netto-Ferreira, J.C.,Avellar, I.G.J.,Scaiano, J.C.
, p. 89 - 92 (2007/10/02)
The photochemistry of a series of 10 α-(aryloxy)acetophenones has been examined by quantum yield, product studies, and laser flash photolysis techniques.Triplet decay involves a competition of β-cleavage with intramolecular quenching by the β-aryl group, the latter being favored in all systems.Typical triplet lifetimes at room temperature range from 60 to 260 ps and are rather insensitive to the substitution pattern. β-Cleavage rate constants range between 1*107 and 3*109 s-1 and are strongly favored by electron releasing substituents, such as 4-methoxy.The determination of true quantum yields of β-cleavage requires the addition of thiophenol as a radical trap to prevent the efficient back reaction that takes place otherwise; under these conditions quantum yields range from 10-3 to 0.14, the highest value being obtained for the 4-methoxy and 4-hydroxy derivatives.
