Computational Study on Kinetics and Mechanisms of Unimolecular Decomposition of Succinic Acid and It
June 29th, 2008 | by admin |Computational Study on Kinetics and Mechanisms of Unimolecular Decomposition of Succinic Acid and Its Anhydride.
The mechanisms and kinetics of unimolecular decomposition of succinic acid and its anhydride have been studied at the G2M(CC2) and microcanonical RRKM levels of theory. It was shown that the ZsgsZ conformer of succinic acid, with the Z-acid form and the gauche conformation around the central C-C bond, is its most stable conformer, whereas the lowest energy conformer with the E-acid form, ECGsZ, is only 3.1 kcal/mol higher in energy than the ZsgsZ. Three primary decomposition channels of succinic acid producing H 2O + succinic anhydride with a barrier of 51.0 kcal/mol, H 2O + OCC 2H 3COOH with a barrier of 75.7 kcal/mol and CO 2 + C 2H 5COOH with a barrier of 71.9 kcal/mol were predicted. The dehydration process starting from the ECGCZ-conformer is found to be dominant, whereas the decarboxylation reaction starting from the ZsgsZ-conformer is only slightly less favorable. It was shown that the decomposition of succinic anhydride occurs via a concerted fragmentation mechanism (with a 69.6 kcal/mol barrier), leading to formation of CO + CO 2 + C 2H 4 products. On the basis of the calculated potential energy surfaces of these reactions, the rate constants for unimolecular decomposition of succinic acid and its anhydride were predicted. In addition, the predicted rate constants for the unimolecular decomposition of C 2H 5COOH by decarboxylation (giving C 2H 6 + CO 2) and dehydration (giving H 3CCHCO + H 2O) are in good agreement with available experimental data.
Chen HT, Chang JG, Musaev DG, Lin MC.
chemmcl@emory.edu, dmusaev@emory.edu.