Computational Evidence Suggests That 1-Chloroethanol May Be an Intermediate in the Thermal Decomposition of 2-Chloroethanol into Acetaldehyde and HCl

Abstract

The dehalogenation of 2-chloroethanol (2ClEtOH) in gas phase with and without participation of catalytic water molecules has been investigated using methods rooted into the density functional theory. The well-known HCl elimination leading to vinyl alcohol (VA) was compared to the alternative elimination route towards oxirane and shown to be kinetically and thermodynamically more favorable. However, the isomerization of VA to acetaldehyde in the gas phase, in the absence of water, was shown to be kinetically and thermodynamically less favorable than the recombination of VA and HCl to form the isomeric 1-chloroethanol (1ClEtOH) species. This species is more stable than 2ClEtOH by about 6 kcal mol -1 -1 ). Thus, it is concluded that while 1ClEtOH may be a plausible intermediate in the gas phase dehalogenation of 2ClEtOH, it is unlikely that it plays a major role in water complexes (or, by inference, aqueous solution). It is also shown that neither in the gas phase nor in the cluster with one water molecule, the oxirane path is competitive with the VA alcohol path.

Conformer Selection by Electrostatic Hexapoles: A Theoretical Study on 1-Chloroethanol and 2-Chloroethanol

“…The molecular geometries of the various conformers and rotamers of 1-chloroethanol and 2-chloroethanol [36,37] were optimized with the Gaussian 09 software package (Gaussian, Inc., Wallingford, CT, USA) [38] at the MP2 level of theory with the aug-cc-pVTZ basis set (Tables S1-S7). The same software with the same level of theory and basis set was also used to calculate the permanent dipole moments µ [39] and their components with respect the principal axes of inertia µ A , µ B , and µ C ; the rotational constants A, B, and C; and the relative energies E for the various conformers or rotamers.…”