Computational Study on the Kinetics and Mechanisms for the Unimolecular Decomposition of Formic and Oxalic Acids
- 6 March 2007
- journal article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry A
- Vol. 111 (29), 6789-6797
- https://doi.org/10.1021/jp069036p
Abstract
The kinetics and mechanisms for the unimolecular decomposition reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory. There are two reaction pathways in the decomposition of formic acid: The dehydration process starting from the Z conformer is found to be the dominant, whereas the decarboxylation reaction starting from the E conformer is less competitive. The predicted rate constants for the dehydration and decarboxylation reactions are in good agreement with the experimental data. The calculated CO/CO2 ratio, 13.6−13.9 between 1300 and 2000 K, is in close agreement with the ratio of 10 measured experimentally by Hsu et al. (In The 19th International Symposium on Combustion; The Combustion Institute: Pittsburgh, PA, 1983; p 89). For oxalic acid, its isomer with two intramolecular hydrogen bonds is the most stable structure, similar to earlier reports. Two primary decomposition channels of oxalic acid producing CO2 + HOCOH with barriers of 33−36 kcal/mol and CO2 + CO + H2O with a barrier of 39 kcal/mol were found. At high temperatures, the latter process becomes more competitive. The rate constant predicted for the formation of CO2 and HOCOH (the precursor of HCOOH) agrees well with available experimental data. The mechanism for the isomerization of HOCOH to HCOOH is also discussed.Keywords
This publication has 30 references indexed in Scilit:
- Unimolecular Decomposition of Formic Acid in the Gas PhaseOn the Ratio of the Competing Reaction ChannelsThe Journal of Physical Chemistry A, 2005
- New Mechanism for the Catalyzed Thermal Decomposition of Formic AcidThe Journal of Physical Chemistry A, 2000
- Role of water in formic acid decompositionAIChE Journal, 1998
- Matrix-isolation and ab initio studies of oxalic acidThe Journal of Physical Chemistry, 1992
- Density-functional thermochemistry. I. The effect of the exchange-only gradient correctionThe Journal of Chemical Physics, 1992
- Unimolecular decomposition of oxalic acidThe Journal of Physical Chemistry, 1987
- The gas-phase photochemistry of oxalic acidThe Journal of Physical Chemistry, 1985
- A critical evaluation of Lennard–Jones and Stockmayer potential parameters and of some correlation methodsCanadian Journal of Chemistry, 1977
- The Effect of Water and of Glycerol on the Decarboxylation of Oxalic AcidJournal of the American Chemical Society, 1955
- PHOTOCHEMICAL STUDIES. IV. THE THERMAL DECOMPOSITION OF ANHYDROUS OXALIC ACID AND ITS RELATION TO THE PHOTOCHEMICAL DECOMPOSITIONJournal of the American Chemical Society, 1926