Theoretical study of the mechanisms for the alkoxyacetic acids decomposition

The decomposition of three alkoxyacetic acids, methoxy, ethoxy, and isoprop oxy acetic acids, has been studied by using ab initio calculations at the M P2/6-31G** level. Molecular mechanisms A and B have been characterized, cor responding to stepwise processes with formation of the corresponding alcoho l and an alpha-lactone intermediate, achieved by the nucleophilic attack of either carbonylic or hydroxylic oxygen atoms followed by a ring opening pr ocess to yield formaldehyde and carbon monoxide. For ethoxyacetic and isopr opoxyacetic acids, three additional reactive channels were thought to be po ssible on potential energy surface; mechanisms C and D are elimination proc esses to give the corresponding alkene and glycolic acid. The reaction path ways along mechanisms C and D take place by the transfer of a beta-hydrogen atom, with respect to the ether group, from the terminal methyl group to t he hydroxylic or the alkoxylic oxygen atoms, respectively. The glycolic aci d formed in the first step is then submitted to decomposition by water elim ination and a-lactone intermediate formation. A final ring opening process yields formaldehyde and carbon monoxide. Molecular mechanism E is associate d with a fragmentation process along a concerted one-step with concomitant formation of the corresponding alquene, formaldehyde, water, and carbon mon oxide. The decomposition process is energetically favorable along the mecha nism A, and the calculated rate coefficients agree with experimental data.