Publication Details

Kato, S., Ellison, G., Bierbaum, V. & Blanksby, S. J. (2008). Base-induced decomposition of alkyl hydroperoxides in the gas phase. Part 3. Kinetics and dynamics in HO + CH3OOH, C2H5OOH, and tert-C4H9OOH reactions. The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory, 112 (39), 9516-9525.


The ECO2 elimination reactions of alkyl hydroperoxides proceed via abstraction of an α-hydrogen by a base: X + R1R2HCOOH → HX + R1R2CO + HO. Efficiencies and product distributions for the reactions of the hydroxide anion with methyl, ethyl, and tert-butyl hydroperoxides are studied in the gas phase. On the basis of experiments using three isotopic analogues, HO + CH3OOH, HO + CD3OOH, and H18O + CH3OOH, the overall intrinsic reaction efficiency is determined to be 80% or greater. The ECO2 decomposition is facile for these methylperoxide reactions, and predominates over competing proton transfer at the hydroperoxide moiety. The CH3CH2OOH reaction displays a similar ECO2 reactivity, whereas proton transfer and the formation of HOO are the exclusive pathways observed for (CH3)3COOH, which has no α-hydrogen. All results are consistent with the ECO2 mechanism, transition state structure, and reaction energy diagrams calculated using the hybrid density functional B3LYP approach. Isotope labeling for HO + CH3OOH also reveals some interaction between H2O and HO within the ECO2 product complex [H2O···CH2O···HO]. There is little evidence, however, for the formation of the most exothermic products H2O + CH2(OH)O, which would arise from nucleophilic condensation of CH2O and HO. The results suggest that the product dynamics are not totally statistical but are rather direct after the ECO2 transition state. The larger HO + CH3CH2OOH system displays more statistical behavior during complex dissociation.



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