54821-21-5Relevant academic research and scientific papers
Reactions of Thermally Generated 1-Adamantyl and Di(1-adamantyl)ketyl Radicals in Toluene
Lomas, John S.,Fain, Dominique,Briand, Sylvette
, p. 1052 - 1058 (1990)
Thermolysis of tri(1-adamantyl)methanol in toluene at 145-185 deg C gives bibenzyl, di(1-adamantyl)ketone, di(1-adamantyl)methanol and a cross-product, 1,1-di(1-adamantyl)-2-phenylethanol, in yields which depend on the temperature and the isotopic composition of the solvent.In the presence of benzophenone the intermediate di(1-adamantyl)ketyl radical transfers hydrogen, giving ketone and the hydroxybenzhydryl radical, the cross-product then being 1,1,2-triphenylethanol.The cage effect (0.38-0.415) has been determined by studying thermolysis in deuterium labeled toluene.In normal toluene almost all the secondary alcohol is formed from Ad2C*OH by hydrogen abstraction from the solvent, whereas in deuterated toluene 22-32percent results from self-disproportionation of ketyl radicals, showing that there is a substantial kinetic isotope effect on hydrogen abstraction.Kinetic modeling of the reaction by means of a rapid, iterative procedure based on the steady-state approximation suggests values in the range 6.0-7.4, decreasing as the temperature rises.
Tri(1-adamantyl)methane and its Thermolysis
Lomas, John S.
, p. 1531 - 1532 (2007/10/02)
The synthesis of the title compound, a new tri(tert-alkyl)methane, and the kinetics and products of its thermolysis are described.
Reactions of Thermally Generated tert-Butyl and Di(tert-alkyl)ketyl Radicals in Toluene: Cage Effects and Hydrogen Transfer
Lomas, John S.,Briand, Sylvette,Fain, Dominique
, p. 166 - 175 (2007/10/02)
Thermolysis of di(1-adamantyl)-tert-butylmethanol (2a) in toluene at 145-185 deg C gives mainly bibenzyl, di(1-adamantyl) ketone, di(1-adamantyl)methanol, and the cross-product, 1,1-di(1-adamantyl)-2-phenylethanol.In the presence of benzophenone (BP) or benzenethiols as hydrogen-accepting and hydrogen-donating radical scavengers, respectively, the di(1-adamantyl)methanol/di(1-adamantyl) ketone ratio tends to steady values as the scavenger/2a ratio is increased, while the cross-product disappears.At 165 deg C the secondary alcohol minimum is 8percent (BP) and the ketone minimum 11percent (thiol).These represent the contributions of geminate hydrogen atom transfer reactions to the overall yields, i.e., the cage effects.With BP the major cross-product is 1,1,2-tri-phenylethanol.Products from the self- and cross-reactions of benzyl and thiyl radicals are found when thiol is present, the diaryl disulfide predominating at high thiol concentration.In both cases, cross-products resulting from reaction of the tert-butyl radical with the scavenger-derived radical are detected in small amounts, being of greater importance in deuteriated toluene.The tert-butyl radical is considered, therefore, to be less reactive in hydrogen atom abstraction than the 1-adamantyl radical.Cage effects for other di(tert-alkyl)-tert-butylmethanols that thermolyze with exclusive t-Bu-C bond fission have also been measured and the product composition of the scavenger-free reaction interpreted by kinetic simulation based on the steady state approximation.Rate constants for hydrogen abstraction by the tert-butyl radical from toluene are not accurately determined by this procedure but seem, nevertheless, to indicate that the literature value (14.4 M-1s-1 at 48 deg C) is an overestimate. Solvent hydrogen abstraction by the ketyl radical shows a small but well-defined steric effect.
Thermolysis of Highly Congested Tri-tert-alkylmethanols: Strain Energies of Bridgehead Alkyl Radicals
Lomas, John S.
, p. 4291 - 4299 (2007/10/02)
The rate constants and the products of the thermolysis of tertiary alcohols, R1R2R3COH, where Ri is tert-butyl, 1-adamantyl, 1-bicyclooctyl, or 1-norbornyl, have been determined.Apart from the usual secondary alcohols and ketones, the products include new ketones, formed by ring opening of the 1-norbornyl group, and solvent-incorporated alcohols.The activation energies for (t-Bu)-C, Ad-C, Oc-C, and, in one case, Nor-C cleavage are compared with the molecular mechanics calculated strain-energy changes, Δstrain.These latter are based on a simple model of the reaction intermediate where the bridgehead radicals are represented by the corresponding alkanes.Taking the ΔG(excit.)(200 deg C)/Δstrain correlation for t-Bu-radical formation as a reference, one can show that the deviations, ΔΔstrain, of the data for the formation of the other radicals (Ad, 2.4; Oc, 4.0; Nor, 7.7 kcal mol-1) indicate the real difference between the strain energies of the radicals and the alkanes.Analogous ΔΔ(excit.) data for other reactions considered to involve rate-determining radical formation correlate with ΔΔstrain, the slopes ranging from 0.16 to 1.13.The ΔΔstrain values also correlate with solvolysis rate constants of tert-alkyl tosylates, with a slope (ΔΔstrain/ΔG(excit.)(70 deg C)) of 0.36; tentative values for the strain energies of other bridgehead radicals are proposed and compared with the predictions of a radical force field.
