2348-46-1Relevant articles and documents
Absolute Rate Constant for the Reaction of O(3P) with Ethanol
Grotheer, Horst-Hemming,Nesbitt, Fred L.,Klemm, R. Bruce
, p. 2512 - 2518 (1986)
The rate constant for the reaction of atomic oxygen with ethanol was measured directly by two experimental techniques: flash photolysis-resonance fluorescence (FP-RF, 297-886 K) and discharge flow-resonance fluorescence (DF-RF, 298-706 K).Kinetic complications in the DF-RF experiments from a fast secondary reaction and heterogeneous effects were overcome by operating at very low initial O-atom concentrations combined with the addition of excess O2.Under these conditions results obtained in the DF-RF experiments were in very close agreement with those from the FP-RF work, which was not perturbed by any apparent complication.The combined results show slight non-Arrhenius behavior and the data were accordingly fit to a three-parameter expression, 298-886 K, k1(T) = 9.88 * 10-19T2.46 exp(-932/T), in units of cm3 molecule-1 s-1, with an error limit of about +/- 15percent over the given temperature range.In addition, initial variation experiments were carried out at 298 K in the DF-RF apparatus to investigate the mechanism of this reaction, and model calculations for an assumed mechanism were performed.Finally, the branching ratios for the three possible H-abstraction channels are discussed in light of the non-Arrhanius behavior displayed in the present rate data.
Determination of Absolute Rate Constants for the Reversible Hydrogen-atom Transfer between Thiyl Radicals and Alcohols or Ethers
Schoeneich, Christian,Asmus, Klaus-Dieter,Bonifacic, Marija
, p. 1923 - 1930 (2007/10/02)
Absolute rate constants have been determined for the reversible hydrogen-transfer process R. + RSH ->/. by pulse radiolysis, mainly through direct observation of the RS. radical formation kinetics in water-RH (1:1, v/v) mixtures.The thiols investigated were penicillamine and glutathione; the RH hydrogen donors were methanol, ethanol, propan-1-ol, propan-2-ol, ethylene glycol, tetrahydrofuran and 1,4-dioxane with the abstracted hydrogen being located α to the hydroxy or alkoxy function.Rate constants for the forward reaction of the above equilibrium (in radiation biology referred to as 'repair' reaction) were typically of the order of 1E7-1E8 dm3 mol-1 s-1 while hydrogen abstraction from RH by thiyl radicals (reverse process) occurred with rate constants of the order of 1E3-1E4 dm3 mol-1 s-1.This yields equilibrium constants of the order of 1E4.Based on these data, standard reduction potentials could be evaluated for the R'R''C.OH/H(1+)//R'R''CHOH, R'R''CO/H(1+)//R'R''C.(OH) and R'R''CO//R'R''C.O(1-) couples from methanol, ethanol and propan-2-ol.Effective hydrogen-atom abstraction by RS. required activation by neighbouring groups of the C-H bond to be cleaved in RH.No such process was observed for the RS. reaction with -CH3 groups, e.g. in 2-methylpropan-2-ol.Several halogenated hydrocarbons, including some anaesthetics (e.g. halothane) and Fe(CN)6(3-) have been tested with respect to their ability to disturb the (CH3)2C.OH + RSH ->/. equilibrium through an irreversible electron-transfer reaction with the reducing α-hydroxyl radical, thereby drawing the equilibrium to the left-hand side.The respective efficiencies are found to be related to the electronegativities of the electron acceptors.The results are briefly discussed in terms of their biological relevance.
