Theoretical Study of Formamide Decomposition Pathways

Abstract

The chemical transformations of formamide (NH(2)CHO), a molecule of prebiotic interest as a precursor for biomolecules, are investigated using methods of electronic structure computations and Rice-Rampserger-Kassel-Marcus (RRKM) theory. Specifically, quantum chemical calculations applying the coupled-cluster theory CCSD(T), whose energies are extrapolated to the complete basis set limit (CBS), are carried out to construct the [CH(3)NO] potential energy surface. RRKM theory is then used to systematically examine decomposition channels leading to the formation of small molecules including CO, NH(3), H(2)O, HCN, HNC, H(2), HNCO, and HOCN. The energy barriers for the decarboxylation, dehydrogenation, and dehydration processes are found to be in the range of 73-78 kcal/mol. H(2) loss is predicted to be a one-step process although a two-step process is competitive. CO elimination is found to prefer a two-step pathway involving the carbene isomer NH(2)CHO (aminohydroxymethylene) as an intermediate. This CO-elimination channel is also favored over the one-step H(2) loss, in agreement with experiment. The H(2)O loss is a multistep process passing through a formimic acid conformer, which subsequently undergoes a rate-limiting dehydration. The dehydration appears to be particularly favored in the low-temperature regime. The new feature identifies aminohydroxymethylene as a transient but crucial intermediate in the decarboxylation of formamide.

Some Insights Into Formamide Formation Through Gas-Phase Reactions in the Interstellar Medium

“…Recently, different decomposition channels of formamide have been reported in a theoretical study by Nguyen et al (2011Nguyen et al ( , 2013. From these results, we can conclude that formation of formamide from the direct products of its decomposition is not possible under interstellar conditions.…”

Formamide and the origin of life

“…Similarly, NH 2 CHO can be hydrolyzed to ammonium formate (NH + 4 HCOO − ) at a meaningful rate. However, one has to take into account the fact that formamide can be regenerated by other synthetic routes described above and that, at difference from HCN, it can be easily concentrated by evaporation of water, having a boiling point of 210 • C and very limited azeotropic effects [58].…”

“…Another interesting property that characterizes the NH 2 CHO as prebiotic precursor is related to the possibility of a partial degradation under the reaction conditions to generate a panel of low molecular weight compounds which are useful intermediates in the prebiotic synthesis of biomolecules, thus increasing the network of possible transformations [58]. This property points to NH 2 CHO as a multifunctional prebiotic precursor.…”

“…All these compounds are possible intermediates in the prebiotic synthesis of nucleic acids, thus increasing the network of possible transformations [64,65]. The chemical potential of H 2 NCHO in prebiotic chemistry was, for a long period of time, considered to be limited to the synthesis of a small number of heterocycles including, as a nucleic base, only adenine [66,67].…”

Infrared spectrum of formamide in the solid phase

“…Formamide, the simplest amide, contains the peptide linkage which is of crucial importance in protein chemistry and physics, since peptide links are known to be the basis for assembling proteins and polypeptides from amino acids. For example, purine, the base molecule from which adenine and guanine are derived, is known to be a by-product of formamide polymerisation [1] and poly (hydrogen cyanide), an important constituent of the prebiotic soup [2].…”