488-23-3Relevant articles and documents
Rates and Mechanism of Proton Transfer from Transient Carbon Acids. The Acidites of Methylbenzene Cations
Schlesener, C. J.,Amatore, C.,Kochi, J. K.
, p. 7472 - 7482 (1984)
The fast rates of proton transfer from various methylbenzene cation radicals to a series of substitued pyridine bases are successfully measured in acetonitrile solutions.The technique utilizes the production of the cation radical as a transient intermediate during the electron-transfer oxidation of the methylbenzene with an iron(III) oxidant.Complete analysis of the complex kinetics affords reliable values of the deprotonation rate constants k2 which span a range from 3 x 102 to more than 2 x 107 M-1 s-1.The relative acidities of the cation radicals of hexamethylbenzene, pentamethylbenzene, durene, and prehnitene can be obtained from the Broensted correlation of the deprotonation rate constants with the pyridine base strengths and the standard oxidation potentials of the methylarenes.An estimate of the acidity constant for the hexamethylbenzene cation radical is based on several empirical extrapolations to that of the toluene cation radical previously evaluated by Nicholas and Arnold on thermochemical grounds.The kinetic acidities of the various methylarene cation radicals are also examined in the context of the Marcus equation, as applied to proton transfer.The mechanism of proton transfer from these labile carbon acids is discussed with regard to the electronic effects relevant to the methylarene oxidation potential and the pyridine base strength, the kinetic isotope effects with deuterated methyl groups, the salt effects in acetonitrile, and the steric effects of ortho substituents on pyridine.
Throndsen et al.
, p. 176,180 (1966)
Reaction routes in catalytic reforming of poly(3-hydroxybutyrate) into renewable hydrocarbon oil
Kang, Shimin,Yu, Jian
, p. 30005 - 30013 (2015/05/13)
Poly(3-hydroxybutyrate) or PHB is an energy storage material of microbial organisms and can be reformed into hydrocarbon oils rich with aromatic compounds. This work investigated the main reaction routes from PHB to the key intermediates and final hydrocarbons. The main sequential reactions under catalysis of phosphoric acid at moderate temperatures (200-230 °C) consist of: (1) decomposition of PHB into crotonic acid, a major monomeric intermediate, (2) deoxygenation of crotonic acid, and (3) combination of the deoxygenated molecules. The oxygen in PHB is removed as CO2 and H2O in stage (2), involving decarboxylation and ketonization of crotonic acid. The main aromatic compounds are formed in stage (3) from propylene and 2,3-dimethyl-2-cyclopenten-1-one as two key intermediates, the former from decarboxylation and the latter from ketonization of crotonic acid. The reaction routes reveal that the formation of aromatics is affected to a great extent by the concentrations of phosphoric acid and water in the reaction, which can be used to control the composition of hydrocarbon oil.
Accurate oxidation potentials of benzene and biphenyl derivatives via electron-transfer equilibria and transient kinetics
Merkel, Paul B.,Luo, Pu,Dinnocenzo, Joseph P.,Farid, Samir
experimental part, p. 5163 - 5173 (2009/12/06)
(Graph Presented) Nanosecond transient absorption methods were used to determine accurate oxidation potentials (Eox) in acetonitrile for benzene and a number of its alkyl-substituted derivatives. Eox values were obtained from a combination of equilibrium electron-transfer measurements and electron-transfer kinetics of radical cations produced from pairs of benzene and biphenyl derivatives, with one member of the pair acting as a reference. Using a redox-ladder approach, thermodynamic oxidation potentials were determined for 21 benzene and biphenyl derivatives. Of particular interest, Eox values of 2.48 ± 0.03 and 2.26 ± 0.02 V vs SCE were obtained for benzene and toluene, respectively. Because of a significant increase in solvent stabilization of the radical cations with decreasing alkyl substitution, the difference between ionization and oxidation potentials of benzene is ～0.5 eV larger than that of hexamethylbenzene. Oxidation potentials of the biphenyl derivatives show an excellent correlation with substituent σ+ values, which allows Eox predictions for other biphenyl derivatives. Significant dimer radical cation formation was observed in several cases and equilibrium constants for dimerization were determined. Methodologies are described for determining accurate electrontransfer equilibrium constants even when dimer radical cations are formed. Additional equilibrium measurements in trifluoroacetic acid, methylene chloride, and ethyl acetate demonstrated that solvation differences can substantially alter and even reverse relative Eox values.
