Theoretical Study of the Mechanisms for the Alkoxyacetic Acids Decomposition

Abstract

The decomposition of three alkoxyacetic acids, methoxy, ethoxy, and isopropoxy acetic acids, has been studied by using ab initio calculations at the MP2/6-31G** level. Molecular mechanisms A and B have been characterized, corresponding to stepwise processes with formation of the corresponding alcohol and an α-lactone intermediate, achieved by the nucleophilic attack of either carbonylic or hydroxylic oxygen atoms followed by a ring opening process to yield formaldehyde and carbon monoxide. For ethoxyacetic and isopropoxyacetic acids, three additional reactive channels were thought to be possible on potential energy surface; mechanisms C and D are elimination processes to give the corresponding alkene and glycolic acid. The reaction pathways along mechanisms C and D take place by the transfer of a β-hydrogen atom, with respect to the ether group, from the terminal methyl group to the hydroxylic or the alkoxylic oxygen atoms, respectively. The glycolic acid formed in the first step is then submitted to decomposition by water elimination and α-lactone intermediate formation. A final ring opening process yields formaldehyde and carbon monoxide. Molecular mechanism E is associated with a fragmentation process along a concerted one-step with concomitant formation of the corresponding alquene, formaldehyde, water, and carbon monoxide. The decomposition process is energetically favorable along the mechanism A, and the calculated rate coefficients agree with experimental data.

Collision induced dissociation of deprotonated glycolic acid

“…A critical concept for understanding fragmentation of glycolate is formation of an ␣-lactone intermediate ion following nucleophilic attack of the carboxylic oxygen on the ␣-carbon. A similar concept for the gas phase reactions of neutral glycolic acid has been postulated before based on theoretical studies on the mechanisms of the decomposition of ␣-hydroxycarboxylic and alkoxyacetic acids [11,12]. We believe that our experimental observations provide a support for ␣-lactone as an intermediate in dissociation reactions of negative ions of glycolic acid.…”

The elimination kinetics and mechanisms of ethyl piperidine‐3‐carboxylate, ethyl 1‐methylpiperidine‐3‐carboxylate, and ethyl 3‐(piperidin‐1‐yl)propionate in the gas phase

“…According to product formations and the kinetic and thermodynamic parameters, the mechanisms of these eliminations may be considered as described in (7), (8), and (9):…”

“…The acid intermediates of ethyl 1-methylpiperidine-3-carboxylate (reaction (8)) and ethyl piperidine-3-carboxylate (reaction (9)) are assumed to proceed through a six-membered cyclic transition state where the chair conformation appears to favor the elimination reaction. In the case of ethyl piperidine-3-carboxylate (reaction (9)), and the corresponding β-amino acid, i.e.…”

“…For ethyl 1-methylpiperidine-3-carboxylate: (8) For ethyl piperidine-3-carboxylate: (9) BIBLIOGRAPHY…”

Theoretical study of neighboring carbonyl group participation in the elimination kinetics of chloroketones in the gas phase

“…In association with the aim of the present work, it is interesting to mention the valuable studies of the potential energy surface (PES) in the mechanistic considerations of the unimolecular the gas‐phase elimination kinetics of several 2‐substituted carboxylic acids 15–20. Calculations at the ab initio and Density Functional Theory (DFT) level of theory showed that the most reasonable mechanism is that which proceeds through the anchimeric assistance of the neighboring oxygen of CO of the carboxylic acid to the C α L bond polarization in the TS [reaction (3)].…”