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• 402-45-9 4-hydroxybenzotrifluoride 

Relevant academic research and scientific papers

Kinetic solvent effects on hydrogen-atom abstractions: Reliable, quantitative predictions via a single empirical equation

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.

Reactivity of substituted phenols toward alkyl radicals

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.